The goal of Portland Guitar fretwork is to create a smooth and soft feeling for the acoustic guitar player, who interacts with the fretboard most of all. A good playing experience is one where there is no buzzing, and there are no hard edges for the hand to run into.
To achieve this goal our frets are dressed, leveled and polished using a few processes. These include dressing the fret ends in a spherical ball. Levelling the frets while the tension is on and polishing the frets using an orbital sander. This varies from other methods in a few ways.
The leveling can be done with a flat sanding block and using feeler gauges to measure the distance from a flat, straight beam. This has problems because of buzzing caused once the strings are brought to tension. This process has been improved by waiting until the tension is on the guitar and the slope from the neck being pulled up is in place. A small flat sander is inserted under the strings and the sanded level. This is fast and makes it easy to remove any erroneous buzzing.
The orbital sander is used over sanding blocks because of speed and ease of use. It does not affect the quality, so this Is an easier way to do it.
This article and video will detail the steps we go through and the important details we watch for when performing each task. There are a few materials and tools to get together before beginning. These are listed below.
Materials Needed:
Sandpaper—400 grit
Right angle iron
Double stick tape
Strung Guitar with fretboard ready for work
Diamond fret crown file
Orbital sander
Sanding and polishing pads from 400-12000 grit
Furniture oil
Paint scraper/razor blade
File with edge shaved off
The following are the pictures of the tools and sandpapers that we used to do these tasks. There are a variety of tools here, some can be purchased at a hardware store such as the right angle iron, while others need to be purchased from a woodworking supply store or in particular cases a luthier supply store such as StewMac.
There are a few tools that require our creation. It is one of the great parts of woodworking to create your own tools and jigs. In guitar making there are many specialized tasks. In this case taking the fretboard from rough to finished. We must make tools for both dressing the frets and leveling the frets. These will be detailed in the pictures below. It is my belief these instructions can be followed. Please send me a message if there are additional steps needed to follow this guide.
First the special file is used to put an angle in the fret.
It is a simple tool, but the alteration is key.
We can take a file that is barbed on all sides and then take it to a sander and quickly grind down the edge.
It doesn’t take much to grind all the barbs off the file. Make sure to wear proper protective equipment while doing this and keep your work area clean of sawdust.
The file is placed at a 45-degree angle to the fret and run back and forth. The key to doing this is consistency.
Count the number of strokes given for the first fret and repeat it for all of them. Try to find a rhythm to help do this, and repeat for both sides of all the fret ends.
Next a diamond file from StewMac is used to dress the fret ends further.
The file is rolled over the end while filing. When this is done in a smooth manner a few times it creates the effect of a spherical ball. One of the keys is to listen to the sound. When there is a light amount of scratching that is even on both sides the job is done. It’s important to keep the file at the same angle while rotating around.
Once satisfied with the work, take a folded paper towel and run it up and down the sides of the fretboard making sure to catch it on each edge. If there are pieces of paper towel on the end of the frets, then it is too sharp and can be rounded off more. This is a simple test and gives a good measure of the progress made.
Next, we move on to levelling the frets. This could be argued as one of the most important parts of the guitar building process. A level fretboard is key to being able to build an acoustic or electric guitar. Fret buzz is caused by the frets being uneven. If one fret is higher than another than it will tap the high one while played and cause buzz. The way to get rid of this is to have a level fretboard.
The way we did this before our current procedure was by using a flat edge and sanding the frets until they were level with the edge. This has a problem, once the tension is put on, the neck will bend at an angle. This is counteracted by the truss rod but sometimes there is too much for it handle. The new method fixes this by sanding the frets after the strings are put on. This means that the neck bow is already in place when we start.
The key tool in this process is an angle iron with a piece of sandpaper attached to it. This is used to reach the frets underneath the strings. The next pictures will detail how this is made.
The pieces needed are turners’ tape, an angle iron and a piece of sandpaper. The sandpaper is attached to the angle iron using a piece of the double stick tape. Press it into place using a clamp to make sure it sticks. Another upgrade to make is to add a handle to the top to make it easier on the hand. This is done by gluing a dowel onto the side of the angle iron.
The guitar is placed on the bridge with the tension on. The sanding device is inserted under the first two strings and then run back and forth. The first fret is avoided because it sets the initial point that the slope of the frets starts from. It is also hard to reach it given the tension of the strings.
The higher frets are preferentially sanded down while leaving the low ones untouched.
This is repeated going under all the strings. It is then done going back the other way for all frets. This step is done because the angle iron is not a perfect 90 degrees. Instead it slants one way so to make an even level it’s best to go back the other way to smooth out any bumps.
To recognize when the frets are level listen for the clack of the frets as the iron passes over it. Uneven frets will create more sound and clank compared to the smooth frets. There will always be a certain amount of sound so it’s the change that’s important to hear. This clacking can also be felt in the hand as it moves over the frets.
To check your progress, play each note on a string. If there is buzz then sand that string. Do this for all strings and when there is no buzzing it’s time to stop. A frequent situation that occurs is a particular fret buzzing in the middle of the fretboard. This is where this process shines. The buzz can be eliminated at the spot by running the file back and forth over the area a few times. This is much more convenient than undoing the strings and then sanding the frets.
The frets are crowned by taking the diamond file and going over them many times until the flat edge of the top begins to disappear. This puts many scratches going along the frets because that is the direction of motion for the file. If we keep this as is, when a player slides the string on the fret it will not be smooth. To remedy this, make successively smaller scratches going in a circular pattern over all the frets with an orbital sander.
The grits used are 240,600,100,2000,6000,12000. The lowest is put onto the sander and turned on to a low setting. The sander is run back and over each fret at and angle. More time needs to be spent with the lower grits than upper grits. The amount of scratches is most at the lowest levels.
The angle that works best is to be as close to the fret as possible with the pad’s edge hitting the fret in front. The sander doesn’t need to go over the top of the fret. It’s important to not change the level on the fret.
After this the fretboard is wiped down with oil on a cloth and that’s it for our fretwork process. The oil that we use is danish furniture oil. There are many that can be used, and we have no preference so far for one over the other. It doesn’t take much to cover the fretboard, so our bottle of danish oil has lasted a long time.
Careful attention needs to be payed to each step of these tasks. The sounds that are made are a key indicator of how much material is taken away and in what way. There are also other ways to gauge your progress such as light reflections. It is important to check your work as well. We try not to be satisfied until all the mistakes we can see and remove are gone.
Through performing each of these steps and paying careful attention to the frets while doing them the Portland Guitar fret process is complete. The result is a fretboard that is level to the point of no buzzing on the fretboard at the lowest possible action. In addition, the appearance of the fretboard is unmatched. The fret ends are a beautiful ball with no edges and the frets themselves are sparkling polished. These provide the owner of the guitar with a pleasant and smooth experience while playing.
Want to have perfect intonation on your guitar: check out the split saddle compensated bridge:
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The next process to approach is marquetry. The same style will be used on this body as the last one. Black-white-black borders on the outside of the herring bone purfling and snakewood binding, as well as on the bridge and heel cap.
Ready to go and waiting for the luthier to finish his coffee.
First, the neck is fit into the heel channel. Binding needs to be put in before it can be sanded down flush with the neck. The channel for it to sit in is cut.
The multi-tool doesn’t cut all the way through, some chisel work is done to create the channel.
The binding is glued in. the overhand is sanded until the neck can just fit in.
The depth must be gotten right.
first black-white-black is inserted into the edge of the binding channel. It is pressed into place then a drop of thin CA fast cure and accelerant Is dropped on top.
After the binding comes the herring bone. It is thicker and bends worse. A heat gun is used to loosen it up to fit into the upper bout. It’s possible to heat it up too much to the point it falls apart.
That process is repated for the binding and done to the top and bottom edge. Here is the final outcome.
Brazilian rosewood is old so some holes need to be filled in.
A piece of amboyna burl is used for the heel cap.
It is inlayed then glued in.
That’s everything for the marquetry. This went much smoother than the last one. Less clean up and detail work will need to be done in the next stages. This guitar is on track to a quick birth. The next step is applying the finish.
Are you looking to take your guitar playing experience to the next level? The time may be right to take the plunge and make a significant investment in a premium acoustic guitar. Finding the perfect instrument may land anywhere in the range of $1000 to $5000. Research is key to finding the best value. Many decisions must be made, the shape, number of frets to the body, size, etc. A higher cost generally buys better features on an acoustic guitar, but not necessarily, as some are executed better than others. There are a standard range of elements in this range. This guide will explain some of the features of a fine guitar and which ones can be tested out in a store.
Part of what to look for when trying to find the best acoustic guitar is the tone and tactile feeling. This contributes significantly to its quality. A better instrument makes learning to play easier and more fun. There’s nothing comparable to relaxing and feeling comfortable with the instrument. A good playing experience eases the soul.
Over my experience as a builder and a player I’ve developed a list that I go through to check guitars for musicality and playability. This covers many aspects such as action, weight, wood hardware and more. If you’re wondering how to choose a good acoustic guitar, use this intermediate acoustic guitar buying guide and these 15 inspection points.
The top is one of the most important parts of the best acoustic guitar. It acts as the vibrating membrane that projects the sound. There are two types of top: solid wood and laminate. The laminate is cheaper and is made from multiple layers of wood that are glued together in flat planes. The structural integrity provided by the grain in a solid piece is minimized. A solid top is made from a book matched set of wood that is glued next to each other. This creates a single plate with even grain. A solid top is a must.
There are a few caveats about the structure and variations on top woods. Common woods are spruce and cedar. High quality pieces have straight grain with the ends not veering off to the side. There are special variations called “figure”. This makes the wood appear to have a flamed or beeswing effect, among others. Another exotic alteration is a torrefied top. This is thermally aged and provides a vintage tone in theory. These are costly and may or may not provide any benefit.
To check for a laminate or solid top, look at the edge in the sound hole. The signature of a laminate is multiple layers stacked together. It’s possible to see a few of these layers in the edges of the sound hole. These are things to know before buying an acoustic guitar.
The wood used for the back and sides plays a significance in how the guitar looks and sounds. Different woods provide different tones. Most back and sides are hardwoods. Indian rosewood is a standard, it has a warm tone with even bass, mids, and highs. Many, many other woods can be used. This is where the cost can change significantly, one set of hardwood to use ranges between $100-$1000.
While in a store, Hold the acoustic guitar by the neck and try tapping the back in the middle and listen for the tone. This is the resonant frequency of the back. Observe the back braces and note how thick they are. An optimal acoustic guitar has a lightly braced back that can resonate.
Twist the pegs a couple of times to detune and tune the guitar. Feel how smooth they turn and how much they twist the string for the amount they turn. They should be smooth and turn easily. Assess how much turning the peg changes the tuning. These are important to see if it will be simple to tune.
In my opinion, minimal effort required to pull the bridge pins out makes for the smoothest experience. When changing strings, it’s a pain to have to pry out the bridge pins or grab a screwdriver and risk breaking them. The bridge pins don’t need to be tight because the ball end of the string wedges itself underneath the top, holding the pin in place.
Notice how the sound changes and how the body reacts to the note. Each guitar is unique and will not amplify the sound evenly. Some guitars want to be played lightly and will have great tone with a light touch, while others can be dug into and will respond in kind to a hearty force. Gauging which type you like more and what the guitar you’re working with is will be important to figuring out if the guitar will work out well.
There should be no buzzing from playing the note. Buzzing occurs from building problems when the frets aren’t level and one rides higher than the other, impeding the fret and causing it to buzz. This can also be caused by not pressing down hard enough on the note, so make sure to press hard.
Some acoustic guitars sustain notes for longer based on the body size and shape, woods, bracing etc. Comparing this is important. Additionally, there are notes die out very quickly and leave a dull sound. This is caused by the note matching in frequency with one of the resonances from the top, back, or body. When these are present it can impede the aural experience.
Neck profiles come in three main shapes: C, D and V. The neck can be of thin, thick or medium thickness. A nice ergonomic feature is to have the neck taper near the body. This makes it easier to reach your hand around and access the upper frets. The profile and thickness you like will depend on how large your hands are. Once you get a sense for what profile you like or are used to it’s easier to research which guitar will work better.
The action of a guitar changes the soul of how the guitar wants to play. The distance from the strings to the fretboard affects the style and tone. There are two places to check the height of the strings, at the 1st fret and the 12th fret. This is a matter of preference for what is liked best.
Notice how much difficulty it takes to fret while moving up the fretboard. The right action is one that feels comfortable.
Measure the stiffness of the top and back by pressing down with 3lb of force. Take a food scale and press into it until you see it read 3lb. This is how much pressure to apply to the top of the guitar. It’s ok to use more until a noticeable change is seen, but 3lbs is the force of a strong pluck so it is realistic to what the guitar experiences. Notice how much resistance the top gives to being pushed on and how far down it moves. This gauges how stiff the top and back are. In an optimal world these are very loose. A top that is less stiff will be pushed down further than one that is stiffer. The stiffness of the top determines how well the low frequencies perform. A less stiff top will push more air out and vibrate more effectively. This test can be an important part of choosing an acoustic guitar if you are sensitive enough to feel the change in how much the top moves.
The top of the guitar in this regard is like a bridge across a cavern. Consider two types of bridges, a rope bridge and a steel bridge. If the steel bridge is jumped on it won’t flex or vibrate in the low frequencies in a visible way. In contrast, jumping on a rope bridge will cause it to move quite a bit. The rope bridge is of lower stiffness than the steel bridge. When the rope bridge moves it pushes up air. Now to translate this to the guitar, imagine a plate shaped rope bridge, this is like a top. The less stiff top will visibly vibrate and push out more air than a stiff top.
Check the mass of the guitar. This is a matter of personal preference and what you’re willing to accommodate. In relation to how well the guitar is made, mass in different places matters, but altogether creates a difficult situation that is hard to separate. Different parts of the guitar have different optimal masses so holding the guitar by itself won’t tell you enough. A lighter top is the most important part. In general, a lighter guitar is more likely to have a lighter top. The type of wood used for the back and sides affects the mass a large amount, making the top’s mass hard to judge.
There are many different finishes and materials used for finish. Decide whether a matte satin or glossy finish is desired. Shine a bright light on the surface of the guitar and move it around looking at the finish of the guitar in the light. It’s possible to see the thin edge over the wood. The light should reflect evenly across the surface. This is a check to make sure the finish is even. It’s important to have it thin for a light top. Look at how the light plays on the top and notice where the light bends and isn’t even.
The next are a few checks on the quality of the craftsmanship or machining. Look at the neck joint—an ideal neck joint is tight with little gap on either side.
Try sliding a piece of paper underneath the bridge. This is only a cosmetic problem; it’s okay for there to be a gap, but it doesn’t look good and can be avoided.
Most guitars include a compensated saddle. Whether this provides the right amount of compensation in the right places is arguable. The slant in the saddle is used to change the scale length on each string. This adjusts the note played slightly from the 12th fret upwards. It moves the note a little flat by shortening the scale length at the higher strings. To check the intonation, play the note at the first fret and check the note at the 12th fret. Ideally the will both be in tune. Use a standard tuner or, for more accuracy, use a strobe tuner. Often the 12th fret will be sharp, which is intonation error. Having good intonation is important to the quality of a good guitar. Good intonation makes playing the upper frets sound better.
The type of pickup the guitar has is important. Great pickups provide excellent tonal reproduction. There are two main types: under saddle and contact pads. The contact pads will replicate the tone and be louder as it picks up the vibrations from the top which is moving more than under the saddle. The use of a preamp with the pickup will allow for more tone control and options.
Conclusion
Consider these 15 qualities when deciding how to select an acoustic guitar. Knowing what to look for in an acoustic guitar can be tricky, but with practice it becomes easier. The methods used to investigate a guitar can be applied to any, whether they are under 5000 or 500. Some of these can be tried out in a store while others require research. Remember, the feeling of the instrument is an important factor. Whether or not it has good specifications or metrics doesn’t mean anything if it isn’t fun to play.
This guide went over the parts of an excellent acoustic guitar, while staying out of the more theoretical aspects of lutherie. When looking for the best acoustic guitar around $1500, this inspection can go a long way. It is challenging and rewarding to find an acoustic guitar under $3000 or an acoustic guitar under $5000.
If you liked this article check out a modern bracing system: Falcate Bracing
If you're interested in doing more research about fine guitars check out out innovative guitar technology and art. Guitar Technology
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After finishing comes set up. This is painless as the CNC makes our nut, giving us pre-cut slots and even string spacing. Getting the height of the nut is easy using a sander. After this there are a few more details, like dots and a truss rod cover, to add.
The body and neck are sanded down to 800 grit to remove all the scratches. Most of the scratches are put in by the drum sander, so using the 80 grit is the most important part. The largest scratches are the most troublesome. This takes twice as long as predicted every time. Once it’s completed the instrument feels amazing to the touch, silky smooth.
The acrylic lacquer is air brushed on. While spraying, It’s important to get even layers. The brush must be held a certain distance away to make sure the right thickness is appled. From what we’ve been able to figure out, finishing is an inexact process. It has many variables that change daily. Temperature, humidity and others affect the way the lacquer dries and cures. What we do is the best process so far that we’ve found through trial and error.
It dries then is sanded down. The amount of time it spends drying influences how hard it is when sanding.
A layer is applied and then sanded off down. The wood is like a landscape, it contains high and low spots. The goal is to raise everything to an even level. The first layers fill in the valleys in the wood, then the peaks are sanded down.
The same is done with the neck
Polished up and looking fine
The bridge is made then glued on. The finish is thin enough on the top that it can be sanded away to allow space for the bridge to be glued on.
The finished bridge. We made some changes to the split saddle bridge since the last time it was pictured. The changes were made to make the presentation cleaner. The saddle plates were turned into a singular saddle plate. The gaps between the edges were eliminate and the edges have a lift tab to remove it. I think it looks better
The nut is made
The neck is put on
The nut is trimmed to size. A pencil is used to pull the strings up then the nut is removed and sanded down. Our sander is a lathe that has a piece of sandpaper glued to the wheel. The variable speed makes it excellent for fine sanding work.
The truss rod cover is put on. In the past truss rod covers weren’t used. We heard feedback from multiple people that a truss rod cover looked better. The thought process behind leaving one out was that in a performance guitar the player wants to have easy access to the truss rod. Unscrewing a cover creates a burden. This was solved by using magnets in the cover and the truss rod slot.
A few more details were cleaned up and presto! the guitar is finished
The next round of pictures will be the final product shoot.
Background
Wood is composed of three main parts, cellulose, hemicellulose and lignin. The first two absorb water easily and form the structure of the tree. They run perpendicular to each other making a dense gird. The last one, lignin, is responsible for the strength of the tree. It is interspersed between the cells and links the cellulose together adding strength and support. Lignin doesn’t absorb water easily and makes it possible for it to be wicked to the necessary cells.
At the base of a tree there will be higher percentage of lignin to the other components. This makes sense as the base of the tree must be stronger because it holds more weight. A branch of the tree however contains a smaller amount of lignin because it is fighting gravity to grow and doesn’t need the added strength.
As a tree ages it goes through many stages. It starts in the ground and grows large. A tree can be 100 to who knows how many years old. While it’s growing the roots suck up water from the ground. This works as a coolant for the plant. It dissipates the heat created by the growth of new cells. The moisture content of the wood is at its most here. Once the tree is chopped down It stops this process. The internal moisture content is set at this point and it can only go down.
If we take a small branch, it will bend with no trouble. We can twist it and turn it into a circle. This is because it is both well hydrated and there is little lignin present, making it less rigid. Once that twig dries out it will snap when bent.
Next the wood is sawn into usable boards and then kiln dried. When the wood still has a high-water content, it’s considered “green”. The drying process makes the wood usable. It is brought down to a moisture content that makes the wood workable. If it is too green than it will compress while in use and shrink. For guitar making we want dry wood it has many useful properties. It’s hard and stiff, among others. Yet it loses that bending ability. To be successful, we must soften the wood for bending.
The wood needs to be convinced to become a guitar. It has spent years and years as a tree and only know one shape. For this reason, going slow will make or break the success of the project.
Bending Wood
The important part of knowing how bend wood for guitar sides is applying pressure to the wood. Whether this is a roller or with clamps, it is a necessity. Something needs to convince the sides to take the shape that we want it to. Sometimes it’s necessary to make a tight turn, so it’s important to apply consistent pressure at each point. Once the wood has taken the new shape it will keep that shape.
We can think of the lignin as a thermoplastic. It is made up of a grid of semi-uniform units linked together. The same way that plastic will deform when heated, so will the lignin in the wood. If we were to only heat the wood, then we would be counting on the internal parts so be heated by the conduction from the outer sides. We need every pore of the wood to be at an even temperature. Therefore, water is introduced. It permeates the cells and wraps around the non-water absorbing lignin, giving full contact for the heat to spread. The amount of water needed doesn’t need to be anymore than what will saturate the wood.
Three caveats to consider:
There are two methods of wood bending to be shown. How to bend wood with heat and water and how to bend wood with less heat and mainly water. One will be with a fox bending machine and the other will be with clamps and a jig.
Clamps
The first method that I’ll show uses tepid water, a sink, jig, oven, and clamps. Quite simple compared to using a steam box, bending iron, heating pad or other equipment. This process is best used on a jig with a natural radius of curvature. The wood can make some dramatic bends despite this.
The strips of wood are soaked in water. It can be warm but will cool down over time. This step doesn’t add any heat to the wood, it’s only to make the water absorb through it. The pieces are left in the sink for about an hour. It can be left in longer but at a certain point the wood has absorbed all the water that it’s able to. The strips are thin enough that this doesn’t take a long time. After the hour is up the strips are tested by giving them a little bend. If it’s pliable then they can be taken out. If they are still tough, then time to soak for longer. The braces need to bend enough to fit into our forms. The forms have nice gentle curves so it’s not asking the wood to bend far. It’s much less than bending the upper bout of the sides, a notorious section.
The four pieces are clamped to one end of the jig. Then a clamp is applied two inches up, then another is clamped two inches from that. This is repeated until the wood is bent around the jig. Before clamping, check to make sure the wood has some give and push it into the form. The clamps are applied closer where the jig curves to force the wood into place.
They come out of the oven. Those clamps absorbed a lot of heat. The heat of the oven absorbed into the wood and turned the water into steam, this steam evaporated in the oven leaving only dry wood left. The temperature is set to 350 degrees. This is enough to prevent the wood for burning but hot enough to get rid of the moisture. This temperature is appropriate for the guitar side bending temperature as well.
Steam has been created in this process. But the steam was not critical to make the wood bend. The strips were thin and wet enough on their own to make the change with clamps.
The jigs are left to cool down and hold the form. It would be a problem to release them from the jig now and have them relax back to a flatter position. If the pieces were wet this would surely happen. They are still pliable and don’t understand what shape we want them to be in. Therefore, we apply heat; it loosens the lignin, evaporates the water and makes the wood hold its shape. At a certain point this is true because we need to dry out the wood, it isn’t useful to use a wet mess.
The Bending Machine
The second method to guitar side bending is using a bending jig. This is called a fox bending machine with a few adjustments.
The idea is to bend the middle section of the side first by slowly applying pressure with the radial arm. A fixture that matches the curve of the side jig is pressed down into the wood by turning a large bolt then held in place. The piece of wood sites on a jig that has the same shape as the side that we want. To get the outer curves two rollers are used. They are held in place by two large springs fixed to the base.
We need to make this machine usable for many different sizes of guitars. We have many jigs that reflect the different body sizes that we used from a 17” bass down to a 6” super tiny model. The holes in the side allow the roller to be positioned in any place. This makes it easy to find a position to set the roller.
The side wood that we want to bend is placed into a heating blanket.
This is a 5-layer sandwich. There is a strip of aluminum flashing, the heating blanket, aluminum flashing, the side and more aluminum flashing. The heating blanket isn’t directly placed onto the wood.
Now comes the most important part: The water. The water is kept in a bottle with a squirting attachment. The water is poured onto the wood in the aluminum sandwich. The goal is to flood the wood and saturate it as much as possible. If there is an ample amount of water the wood will not burn. The heat will spend all its time evaporating the water,so, it won’t have time to burn the wood. The water acts as a heat conduit to evenly heat the wood. Water is continuously added. The heating blanket is turned on and put on a timer. Once about 5 minutes pass the wood sandwich is at a good temperature and begins to steam. Water is added where needed to keep it steaming.
An interesting point to note is that when the water is added the wood doesn’t bend under it’s own weight. Only after the side starts getting heated up does the side began to collapse. It’s easy to see that the piece is ready to bend because the wings not on the mold sag down from their own mass. This shows that the heat is a necessary component to softening the wood.
The steam permeates the wood to make it pliable. It is placed on top of the side mold and the screw with the shoe is placed above it. The screw is slowly applied to the wood until it starts to bend. During this phase, the screw is rotated until maximum pressure is applied. One of the techniques used is to screw it in, wait a few seconds then release the pressure and move forward repeating staggered steps.
Once the main screw is down the rollers are rolled over the top and lower bout. The pressure is slowly applied to bend the remaining section down into place. Then they are held at the end to keep it in place.
The bend is completed and now it’s time to make sure it stays this way. This is where the heat helps the most. It will dry out the wood and make it conform to existing shape. The blanket is left on for a few minutes then turned off. The sides are kept in the fixture for around 30 minutes until all the heat has dissipated. At this point the sides are removed and clamped into the form mold.
The sides are bent as well as the curfing. The curfing is already bendy because of the wood removed between each post. It’s still a good idea to send in through the bending machine to make it form the right shape. This is an easy job to do because it’s already flexible.
The wood is then returned to its mold and clamped into place. This is an important step to do to prevent the wood from relaxing back to its original position.
Conclusion
These are the two ways that we bend wood for guitars. One using only water and one using a combination of water and heat. It is possible to bend wood around soft curves using only water and clamps and tighter curves use fixtures and mechanical pressure. These methods are applicable to any way that wood is bent. First the wood is made to be hot and moist then it is conformed to a shape. It doesn’t matter what is being bent these are the steps to follow. Go slow when applying pressure and make sure that there is enough water in the system! It’s ok to break a few pieces, after all wood grows on trees.
Check out an article about the advantages of a handmade guitar and check out an article about guitar intonation
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The advantage of a handmade instruments over a factory-built guitar is that the luthier-built guitar is optimized. A factory-built guitar is produced so that it does not come back for warranty work. Companies working to sell many guitars don’t want them to come back with problems. They are overbuilt. This affects the sound quite a bit and dampens the volume, response and sustain. There are many voicing considerations that are much easier when working by hand and when designing for an optimized tone. Another reason is that In a factory the only goal is to make the guitar, there is less care put into each piece and the unique wood that is being used. When building by hand each piece and part is considered on its own and as part of the whole. There is more spirit in this guitar.
We fight against the standard of planned obsolescence in products. Our instruments are made to hold up over time. We have three goals when designing and building an acoustic guitar. These are to make it sound good, to make it play well and to make it last for a long time. By achieving these goals, it creates an instrument we are satisfied to give to the world. In the following I’ll go into the details of what our guitars do to stand out in each category. Portland Guitar has a variety of inventions and innovations that work to satisfy these goals. As well a combination of hand craft and high precision machining used to deliver a quality guitar.
We make instruments that have playability at the forefront of our minds. The way we design and build guitar revolves around making a good user experience. We use a variety of hand tools and computer-controlled machines to achieve this. In combination with our innovative technology we strive to make an experience tailored to you. From a normal builder the guitar that is built is the guitar you’re given. With us we build the guitar so that it can be adapted to your style.
The action is set medium low at the first fret. We can personalize this. After you’re playing session, if you’d like it slightly lower or higher, we will create a new nut built to your desires.
As you travel up the fretboard the action once again may be too high or too low to your preference. In this case our easy adjustable cantilever neck allows you to make changes to the action on the higher frets. A hex key can be inserted into the heel of the neck, where the strap pin is. A bolt inside is turned slightly with the key and the neck angle changes. You’re able to perform a neck reset in seconds and change the action up the fretboard.
Check out adjustable neck
As the guitar ages and becomes accustomed to the tension on it, adjustments to the truss rod will need to be made. This is accessible from the headstock, elegantly built into the design.
The saddles are split because of our perfect intonation bridge. This allows us to insert a shim underneath any string. This lets us change the action for each string. These changes allow the action of each string to be dialed in.
Check out split saddle bridge
The fingerboard angle can be set so that it comes over the top of the body. At this angle there is a gap between the top and the fretboard. This “floating fretboard” makes the higher frets easier to access.
The neck is hand sculpted at the end to ensure it is smooth and even throughout with a comfortable taper. If needed, we can swap our necks out. If you prefer a different neck radius but like how a body sounds, we can make a new neck to change it out with.
After the importance of playability, the next most important feature that we focus on is musicality. We want this guitar to sound good. We want to build for crisp notes with bright highs and deep bases. Making these instruments sound good is much more art than science. Each change that we make might have some effect on the tone, but it isn’t until it all comes together that we can derive a result.
The sound of the guitar mainly comes from the shape of the body. We follow a martin style shaping. A bulbous lower bout and a curvy upper bout. It is made to look natural. The bodies allow for enough air to enter to make a loud sound.
The next part that affects the tone is the woods used. Only the highest quality woods are used in our instruments. Our woods are quarter sawn grain or close that has been aged and dried. We never use laminate woods and stick to two-piece tops and backs.
The frets are routed by machine. This ensures that they are perfectly spaced and creates an articulate fretboard. Each note is at an optimal space between the others.
The next most important part that affects the tone is the top. A lighter top makes for a more responsive guitar with brighter notes overall. There is longer sustain and a slower decay of each note as well. A lighter top can transmit the energy from the air into the body and act as a coupled oscillator more effectively. We achieve this through a variety of methods. To begin with the top is sanded down evenly to a minimal thickness. This opens the top up to the higher frequency resonances. The edges of the top are sanded thinner than the middle to provide a more constrained surface for the edge to sit on.
Our bracing is optimized to allow for strength along the length of the top and flexibility laterally. This makes for the higher order resonances to come out more. It creates a more responsive top as well because of its lightness in structure.
Check out falcate bracing
The air-brushed lacquer finish is made to be as consistent and thin as possible. This keeps as much weight off the top as possible as allows it to be more responsive.
The intonation is perfect. The compensation at the 12th fret allows for the right amount to be used regardless of climate, strings, or playing style. The adjustable saddles can be moved back and forth to make the sound right.
The braces are optimized to be the perfect blend of strength and flexibility. The top is stressed by a tension arm and the braces are sanded down until they provide enough support to withstand 160-180lbs of tension. This is the tension applied by the strings. By doing this it ensures that the top isn’t over braces and ensures that it will be the most responsive.
Before each guitar goes out each fret is checked for buzzing. If there is then an adjustment is made to correct it until there is no buzzing left. We want to make sure this sounds excellent.
The next goal that we strive to build for is longevity. It is said that the guitar is created so it’s on the edge of tearing itself apart. The stress from the strings creates forces that want to rip the guitar apart. The strength of the joints, the evenness of the parts and the hardware used will determine whether the guitar will last of breakdown. To our benefit they are made from wood which is durable. A well maintained and cared for guitar can last generations. It’s our goal to make this guitar a part of the world for as long as possible. It’s a fact that the guitar will undergo changes as they age. The neck will sag due to the tension from the strings. The top will belly due to aging and tension and a myriad of other changes that happen. Portland Guitar builds to counteract and work with these forces.
There is carbon fiber included in our braces. This counteracts some of the bellying that occurs over time. As the wood ages and expands the graphite doesn’t, it holds everything around it in place. Thus, keeping the top from moving out of shape.
As the neck angle changes over time a normal guitar would need a neck reset. This one will never require that. With a turn of the adjustment bolt the neck angle can be changed. This adjustment ensures that the guitar remains playable through time.
We use the best hardware we can. That is Gotoh 510 tuners. They have an excellent gear ratio and don’t breakdown.
Countless hours are put into each guitar. The combination of high-tech machining and hand-crafted finishing creates the perfect environment to build a quality instrument. Many hours go into designing the files to run the computer-controlled router. There are many setbacks and tools that break on the way to making a process that is repeatable and yields the right result. This work is done though to give the most precise parts from fretboards to necks and nuts. With the heavy lifting done this way more time can be spent working on the details of the instrument. Hours are put into hand sanding out each scratch. We look at the wood with a magnifying glass to find them.
Our frets are flat and beautifully dressed as pearls. The CNC creates flat surfaces that the frets sit on ensuring that there is a large amount of fret crown. The frets are shaped minimally because of this precision. The frets are sanded to a 0.001” precision between all the frets. This ensures that there is no buzzing and the feeling is smooth and natural.
Our finish is a water borne lacquer. This is a wonderful finish because it forms a hard shell that is resistant. The finish is applied to be as thin and even all the way through. This keeps the weight of the top and the rest of the body down. It is a brilliant high gloss natural finish that brings out the characteristics of the wood and has a mirror shine.
Jay is a mechanical engineer who has worked with wood his whole life. He understands its structural properties and what makes it work and fail. He worked as a failure analyst for many years. This experience imparted a drive to make objects that don’t fail. Making something that lasts is the greatest gift to give. As such Jay stands behind his instrument and will fix any problems that may come up.
Every guitar is unique, and each takes a different route to creation. Jay loves each guitar like a child and hates to see it go. So, he hopes that it goes to a good home where it’ll get played often. We strive to be your personal luthier. From the initial setup to maintaining and caring for the instrument. We want to make sure that this guitar fits you and your playing style. Our unique innovations allow for these guitars to be modeled after what you want and not what we want as builders. There is an immense amount of options you can choose for this guitar. With easy and quick adjustments, there are many actions that can be played at and different sweetness that can be added using the intonation adjustments. From one guitar many are playable.
A good guitar makes playing easy and fun. The setup, sound, feel and interaction you have with the guitar changes based on how it was built and how well it was built. Some people will play a bad guitar for a long time and become familiar with it, then years later they get a better guitar and admit that the first one was bad the whole time. If you can cut that off and get a good guitar at the beginning it makes the entire process of playing guitar more fun. By interacting smoothly with the instrument, it requires less thought to play. When you can feel the response of the guitar in your body and it sounds crisp it’s easy to get into the zone. Once that happens it becomes secondary to play. Every guitar forms an intimate bond with the player. It is a device that humans use to express emotions and feelings, so it becomes very personal to use. Music is a very deep instinct within us. Guitars have existed for a long time and by using them taps into that. There are different guitars for different times, some feel comfy and others are fancy. There is a guitar for every purpose.
We want to deliver a guitar that sounds good, plays well, and will last a long time. This is achieved through a variety of methods. We have innovations and inventions that accomplish this as well. If you have any questions of comments please let me know.
Check out more about falcate bracing
Check out more about adjustable neck
Check out more about falcate bracing
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What follows is first a breakdown of the improvements that were made and an analysis of them with graphs. The next piece is a photo diary of making the bridge retrofit jig.
For our purposes we will measure the difference between the actual note and the desired note and plot the differences on a graph. In these graphs the note played is plotted on the horizontal axis and the difference between the played and desired noted is plotted on the vertical axis. The vertical axis is measure in cents (100 cents to the half step). To aid in the analysis a linear least square fit is applied to each graph. The graph below shows the results of the E6 string of the Seagull guitar before the split saddle bridge was installed. We can see that the notes trend sharp as the string is played up the fret board.
For comparison purposes the results for the E6 string after the split saddle bridge was installed are graphed below.
We can now see that as the string is played up the fretboard the linear fit is constant. We also must note that there is still significant variation from the ideal. This is for the most part a consequence of the physics of the vibrating system we call a guitar.
The following graph shows all of the results for the Seagull guitar before the split saddle bridge was installed. We can we that in total the guitar tends to play sharp as it is played up the fretboard.
The following graph shows the results for all of the strings after the split saddle bridge was installed.
We can see that we have adjusted the intonation so that the trend lines are nearly constant.
The following graph shows an expanded view of the final results without the trend lines. We can look at each individual note on a string and compare its intonation to the rest of the notes on that string, or we can compare a note to the equivalent note played on a different string. The ideal would be for all of the individual notes to lay right on top of each other. This can be approached by installing a split saddle nut. Nonetheless, the results are pretty good.
A note and comment on the feature in the graph around the D#. We can see that the intonation suddenly goes from somewhat flat to somewhat sharp. This is a repeatable and consistent feature of all guitars. This guitar has an air resonance at the D#. When a note is played near but below this resonance it will play flat and if the note is played above the resonance the string will play sharp. This is a feature of the physics of resonant systems and is one of the phenomena that makes a guitar sound like a guitar. If you tried to make this go away you would end up with a 2X4 with strings.
Here is our photo journal of how we changed the acoustic guitar bridge.
Here is the seagull fresh onto the bench. The strings must be taken off.
The saddle must be taken out. It appears there was a shim underneath to lift up the saddle in the bridge a little bit.
First the saddle plates are made on the cnc
Then the saddles are routed out.
Here is one of the saddles put together
The plan in making this acoustic guitar bridge retrofit jig is to make a plate which will hold a router so that a channel can be made in the right place. The top plate makes the shape needed available
Here it is tested out on a piece of scrap wood. And it works.
Here is what it will look like
The mounts to hold the guitar are installed. The jig is complete, it’s ready to use.
Foam is placed on the guitar to protect the surface of the guitar.
Placed on the guitar. The side mounts are adjustable and squeeze the outside of the guitar providing a sturdy surface to route on.
We’ve got to hold the guitar down, so elastic bands are used because they won’t scratch the finish.
Clamp on
The pegs are drilled out and filled in.
The router in action
Here it is after the first pass. It’s always a good idea to go slow.
Complete
The saddle plates fit like a charm
The new pin holes are drilled
It is complete
IIf you liiked this check out how to get perfect intonation
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The plan is to get two rails and put sliders on them, mount this to the band saw table then use a pusher with compressible but rigid bumpers to hold the wood.
Jay is excited to start a new project. Going to the hardwoods store is like being a kid in a candy shop. He decided to get some high quality 13-ply plywood. He’s using his circular saw to cut up the board into appropriate pieces.
Cutting on the chop saw.
Here are the rails that will be used. They are bosh T-slots. The sliders on them are very smooth, the plate will provide a good surface area for the board.
First the bottom beam was mounted. If the beams aren’t parallel the sliders will veer off and the plate holding the wood will not slide. To make the beams parallel these steel gauge blocks were stacked at each end and the other beam was placed on top of it then was fasten in place.
The sliders work seamlessly.
Smooth. The part on the right on the blade, holds two rollers to assist in the slide. They sit on silicone bumpers the are stiff but still have some give. These help push the board in and hold it in place.
The back holding the rails is clamped into the band saw bed. The angle that this piece is at will affect how straight the outcome will be. To provide wiggle room two bolts are put in the back that act as set screws and are perfect for adjusting the angles.
It’s hard to hold and push the board for 20 minutes to achieve one set. At that rate it takes a lot of patience, when that wears out, it’ll be worth it to purchase a high-power machine. To fix this problem and automate the system a pulley with a weight on the ended was added to provide enough force on the board to pull it through the blade. We can now walk away from it while it works. The amount of force needed to pull the board is small, so a five-pound weight suffices.
Here it is working up close.
The complete project. The wood we resaw rests on a 12 inch piece of wood on the sled. This lets the clamp work.
The result is good. We get about .22 in at one end. And .20 at the other. 10% variance is acceptable.
As more experience is gained using the jig and with different woods it will become easier. The next wood used will be box wood to make purfling.
Here are two videos of it in action
Cutting through a piece of zebra wood
Check out more with the CNC in the shop<.a>
]]>The split saddle bridge is Portland Guitar's patented invention. It is a bridge that does not have a one piece saddle. It has six individual saddles, one for each string. They can be moved back and forth in order to adjust the compensation. This makes it possible to achieve perfect intonation for each note. Additionally non EADGBE tunings will benefit from having a personalized intonation profile. The saddles can be moved back and forth while under tension. This is done with a wood tuning fork. It is easy to use a strobe tuner to measure the open note and 12th fret in order to hone in on the intonation.
A video showing the split saddle bridge in use:
William Compiano, the insightful author of the seminal lutherie book, Guitarmaking: Tradition and Technology, has astutely described the guitar as a cultural artifact and prescribed evidenced based processes to improve the quality of our instruments. We have a history and a relationship, and embrace a set of expectations surrounding this phenomenon we call a guitar. Reasonably, one of the things we anticipate is that the guitar should play in tune. Not surprisingly, it turns out that guitars sound better when they are in tune, but tragically few if any of us have ever actually heard such a guitar. We can use mathematics and a knowledge of physics to design a perfectly intonated guitar and to tell us where we should install the frets and saddles precisely and accurately… theoretically. However, the physics of a real world instrument will make our guitar play the actual notes somewhat inaccurately. The degree to which our real instrument approaches the ideal can be considered a measure of the quality of the instrument. Happily, this measurement is only tedious, and not too difficult. It would be to our benefit if we could adjust the intonation of our guitars once they are set up so that they do play in tune or as close to it as possible.
The following pages describe a method to make an objective and useful measurement of the intonation quality, a practical method to approach the ideal, and the assessment of a variety of guitars for comparison purposes. This comparison demonstrates that the described intonation process improves intonation by several factors.
On these following pages I reference a guitar intonation system designed for an acoustic guitar, diagramed below in Figure 1. The system employs both a movable nut and a movable bridge. The system in theory is well known and the mathematics has been fully described elsewhere (see Gore & Gilet).
In addition this system takes advantage of a User Adjustable Tilt Action Neck that allows the action of the strings to be changed from high to low. The feature is fully described below.
The Equal Tempered Scale (the goal, for good or bad)
Strings vibrate with a fundamental frequency and a set of overtones, or harmonics which we can use to compose a pleasing 12 note scale. Each key in this “just tempered” scale has a certain sound associated with it. That is, if we play a song in the key of C, it will sound very different than when we play the same song in the key of F. This is because the just tempered scale is made up of 12 unequal steps. Two separate intervals in the scale may or may not sound the same. This scale sounds interesting, natural and pleasing, but has the unfortunate property that a keyboard or fretboard that is tuned to this scale can’t transpose a song into another key without changing the sound and character of the song. As the story goes, to correct this problem, in the 17th and 18th century, about the time pianos became popular, our Western European culture (or the piano technicians) chose to split the octave into twelve equal parts, called an “equal tempered” scale. Each interval sounds the same as every other interval. This means that most of the notes don’t fall on the natural notes of the just tempered scale anymore, and the scale should sound wrong. It however does have the happy result that we only need one keyboard or fretboard to play in all of the keys. Luckily our brains are very accommodating and we have learned to like, expect, and anticipate the uniform intervals of our equal tempered scale. In fact, anything else now sounds wrong, exotic, or strange to us. Be careful though, this is a cultural bias, other cultures have different scales that sound just as good and natural to them as ours does to us. Go forth and forage…
Intonation and the Intonation Quality (IQ) Number
By definition, intonation is the accuracy in frequency of a set of notes compared to a standard. We have generally agreed that our standard is to tune concert pitch A to 440 hz and divide the octave into 12 equal parts. The precise frequency of each note is easily calculated and is derived elsewhere. To help enable the useful assessment of our instruments, I propose Intonation Quality (IQ) as an objective measure of this accuracy. In technical terms the quality or Q of a resonant system is defined as the frequency of resonance divided by the full with half max frequency spread of the resonance, i.e., Q= Frequency/(Delta Frequency). This means that a high Q system has a clear piercing tone, while a low Q system has an indistinct muffled tone. For example, a brass bell is a high Q system while a feather pillow is a low Q system. A high Q number means less variation and higher quality while a low Q number means more variation from the center. Remaining consistent with this definition I propose an Intonation Quality number as:
IQ = 440hz/(Average of Intonation Errors) = 100 *440/(Ave. %Error*440) = 100/Ave. %Error
The average is calculated by taking the average of the absolute values. This is because the errors are both positive and negative and we want a measure of how far they are from the zero line.
For example, a guitar with an average error of 1.8 cents would have an IQ number = 100/1.8 = 55.5. As long as the testing protocols are the same these IQ numbers can be used to objectively and directly compare the results of one guitar against another and more importantly they can help us get our guitar pretty well intonated.
The IQ number is the most important of a variety of statistical metrics that are useful in analyzing the quality of intonation. A list of some other metrics are included and explained below in the Analysis section.
A Method to Measure the Intonation Quality
The primary method of determining intonation quality is to measure the frequency of each note on the guitar and compare them to their ideal frequencies and then calculate the errors. The average value of the errors, the median, kurtosis, and the standard deviation are also calculated. Thankfully a spreadsheet makes short work of these calculations and helps keep everything organized. The data can be presented in a variety of ways for visualization and analysis purposes. The intonation errors of each individual string can be can be plotted, and the combined plots for each string can be graphed together to get an overall visual sense for the intonation quality of the instrument. Fig 2 is an example of an aggregate plot. A more thorough explanation is given in the analysis section. The horizontal axis is the note and the vertical axis is the number of cents error. To be in-tune we want the notes to play as close to the zero line as possible. The farther away the note is from the zero line, the more out of tune it is.
A Special Note on Frequency Measurement: There are a variety of tools available to make the necessary frequency measurements. Primarily we need a tool with a digital readout with at least 4 digits of precision. Current smart phones provide inexpensive access to a number of applications that meet this criterion. These apps often provide a full set of features for evaluating frequency and energy. When we make these measurements we are trying to write down the single best number that represents the frequency of the note. This is however a moving target as most notes start sharp and drift flat. Other notes can oscillate, and other times they just act weird. The problem is to be consistent in how we pick the right number. Making multiple measurements is highly advisable. At this point practice makes perfect, or pretty good. A second option is to use an audio spectrum analyzer. A spectrum analyzer has the advantage that it gives the spectrum of the notes rather than its time signature. From the spectrum we can directly read the frequency. The disadvantage is its cost and time to make measurements.
Figures 3 - 8 show the results for the six individual strings of my latest lutherie effort TH 3.1.75 (Fig 25). a mid-size steel string guitar with Tilt Action Neck (Fig 14), Split Saddle Bridge (Fig 16) and Split Saddle Nut (Fig 17). The aggregate results are shown in Fig 2. The individual graphs will be used to make adjustments to our intonation system when we set up the guitar. The aggregate of these data will be used to calculate a set of statistical metrics that will help us understand how we are improving or not.
To help flesh out all of the ways things can go wrong with a guitar’s intonation, the following is a list of possible sources of intonation error. The magnitude of the errors varies, with some sources such as fretting the string causing large effects and others such as finger pressure producing small effects. This list is probably incomplete and is not in any order, but for our purposes it should cover most of the bases.
Psychoacoustics: In our musical convention, the interval from one note to the next is subdivided into 100 equal parts called cents. Individuals have varying levels of ability to hear differences in pitch. It has been reported that we can typically hear an intonation error of about 3 cents at 500 hz although this is not universally accepted as some people can hear better than others. Someone with perfect pitch will hear errors far smaller than I ever can as I am relatively insensitive to pitch. I have been tested and I can only reliably differentiate two tones 12 hz apart at 500 hz… not too good.L Probably why I can’t really sing.
No matter what the numbers from our sophisticated set of tools tells us, if the player says it doesn’t sound right, then it must be adjusted. This is a consequence of the phenomenon that frequency does not equal pitch. Frequency is how fast it vibrates; pitch is how we perceive it and the two just aren’t necessarily the same. We humans have pitch meters not frequency meters in our heads. The subject of psychoacoustics is the study of the perception of sound by the brain and is the last link in a long important chain from the pick to perception.
Fretting the String: When a string is pressed down and fretted its total length increases slightly. Consequently so too does its tension. This increased tension will cause the note to play sharp. The higher the action the more the tension increases which causes the note to play sharper, the lower the action, the smaller the effect. The amount of stretching and the intonation errors depend on where you play the note on the fretboard.
String Height at the Nut: The height of the string at the nut largely determines the amount of additional stretching the string experiences when it is fretted near the nut. The higher the string the more stretching occurs and thus needs additional compensation. This suggests that getting the nut height as low as possible may be advantageous although there are reasons to increase the nut action. A common method to create a nut is to place a fret at the nut position, i.e., the Zero Fret. This creates a nut action nearly identical to the action at the first fret.
Resonance Interactions: Sometimes the resonances of the guitar body can interfere with the string resonances and cause a note to play sharp or flat depending on circumstances. These errors are real, reproducible, and difficult to track down and correct … so far.
Virtual Saddle Position: As the top vibrates the bridge is carried along with it meaning that our supposedly fixed saddle is no longer in a fixed position. If this didn’t happen our guitars wouldn’t make much sound at all. Imagine the string as it vibrates; it takes on a curved shape that comes to a point right at the saddle. On a real guitar though the saddle is still moving, so the imaginary fixed point is behind the saddle a bit. This effect has the result that the string thinks it is longer than it really is. It is sort of like looking into a mirror that is slightly convex; objects are closer than they appear. The problem for the string is to find the virtually fixed position of the saddle. Fortunately it doesn’t find this hard to do. This effect depends on the note, the resonant frequencies of the top of the guitar and how they interact.
String wear and tear: As strings are used they wear away in spots, particularly at the frets, and unevenly collect gunk from the oils, acids, and dirt on our hands. Corrosion can occur anywhere along the string and is likely to be spotty. All of these things cause the string to have an uneven density along its length. This can cause the string to play sharp or flat depending on what has happened to it and where it is being fretted.
Systematic Errors: When a musician frets a note it is possible to push on the string parallel to the frets causing the note to play sharp. This “bending” must be considered if the player systematically does this. It is also possible to press on the string perpendicular to the fret either toward or away from the bridge causing the note to play sharp or flat (vibrato). When a string is pressed down between two frets the tension will increase as it is pushed and stretched further into place. This will cause the note to play sharp. The effect is small, but real, and the harder you push the sharper the note. Someone with a very strong grip may play the note sharper than someone with a light touch. Also, as you play you may change your finger pressure depending on the passage being played. How a person plays has an effect on the intonation and is a factor when setting up the guitar.
Seasonal Changes to the Guitar: As the environment or seasons change, a wooden guitar will expand and contract along with the humidity (mostly) and temperature. The length and shape of the guitar will actually alter slightly. These changes will cause the intonation to drift either sharp or flat depending on the season. The guitar certainly needs to be re-tuned and the IQ number may or may not be affected.
String Mechanics: If you carefully listen to or measure the frequency of a plucked note on a guitar you might notice the tone is not constant. Generally, when the note is first plucked it will play a few cents sharp and then as it decays away the tone drifts back to an asymptote. What is the right tone? Well, that is pretty much up to you. For example, if you play lots of black notes, i.e., notes of short duration, you might choose to intonate the guitar to the first part of the note. If you play lots of really longs notes you might want to intonate to the asymptote. This is truly a subjective decision.
Temperature Changes: Metal strings are particularly susceptible to changes in temperature. The metal will expand as the temperature increases causing the string to lose tension and go flat. Believe it or not, the strings actually warm up as they are played, but this effect is very small. However, if you bring your guitar in from a cold car into a warm room, it will likely be out of tune. Wood also expands and contracts with temperature, but much less than metal.
Changing Strings: When changing strings, the type, make, and gauge of the strings will have differences that may or may not affect the intonation. When changing to a new type of string you might expect the IQ number to change. New strings will be different than old used strings of the same make.
Changes to the Setup: Sometimes you may want to change your playing style and choose to modify the setup, or the guitar gets old or sold or passed on. A little lower action might be nice, or it might be good to just tighten things up once in a while. This may change the intonation depending on what is done. For example when the action is lowered, the strings will stretch less when they are fretted and the intonation errors will be different and require a different amount of compensation.
Neck and Body Creep: Our poor guitars are expected to withstand 160 pounds or so of tension for fifty years or more without deforming more than a millimeter. You try that! All the while the guitar is expected to be as lightly constructed as possible to enhance the acoustics of the instrument. This might be considered a set of unreasonable expectations if one were reasonable, a trait sometimes lacking. In the real world our guitars are in the slow motion process of collapsing under tension. For a high performance guitar that is built on the cusp of self-destruction the effect might be expected to be larger than on an overbuilt off the shelf guitar. Over time the neck angle will change, the top of the guitar deforms, and the woods age and mature. All of these things can make the intonation change and might require the guitar to be adjusted, or worse a neck reset, or worse yet a new top!
Fret Position and Saddle Placement Errors: We know with exquisite theoretical detail where the frets and the saddle belong on the instrument, but it can be difficult to get them positioned just right. With our modern tools we can cut the fret slots to a few mil (1/1000”) accuracy. When cut by hand the slot positions are probably less accurate. When the frets are re-crowned it is important that the peak of the crown is directly over the slot. If any of these things parameters are off even a little bit the only solution may be to rework the instrument. It might be possible to compensate for the errors, but I can’t imagine that it will make the situation much better if the guitar is fundamentally flawed.
Bad Strings: Sometimes it has been reported that a string is unevenly wound or has other manufacturing problems. The best solution if this is the case is to replace the string.
Saddle Slop: For a straight line slanted saddle, if the saddle doesn’t fit snuggly into the saddle slot it can tilt forward leading to errors.
Setting up a Guitar
Among other things, the playability of a guitar is greatly influenced by the height of the strings above the fretboard (the action). Generally, the higher the strings are set above the fretboard the harder it is to play, the lower the strings the easier it is to play. The height of the strings also has an effect on the quality of the sound that the guitar makes. Set the strings too low and the sound gets thin and ultimately starts to buzz as they hit the frets. Make the strings too high above the fretboard and it sounds great but is too hard to play. Once the action is ultimately set, a refinement is achieved by controlling the longitudinal shape of the neck with the truss rod. Ideally there is a slight concave bow of about a millimeter or less at the 12th fret that helps to prevent buzzing. So, for each and every guitar and musician there should be a setup that makes the player most happy. Our objective is to find that happy medium and then make the guitar sound as good as we can with what we are given. Once we have adjusted the action of the guitar and it plays the way the owner would like it to play, it may or may not play in tune; probably not. What to do?
Fortunately, to improve the intonation, we can adjust (compensate) the scale length, defined as the distance from the nut to the bridge, by repositioning the nut and the saddle. It has been traditional to compensate a guitar by making the bass side of the saddle about 1/8 inch farther away from the nut and then further modifying the saddle for each string. This is the slanted saddle seen on most steel string acoustic guitars. This slanted saddle has the effect of increasing the scale length of each string and typically will produce a good but not great intonation. However, good may not do it when we are trying to build a high performance guitar. So we also have the option to adjust the position of the nut. This is a bit more difficult than the saddle adjustment, but not impossible. Nut Compensation has typically been done by fixing the type of strings that will be used, measuring the stiffness and action accurately and precisely, and then using that information and a theoretical formula to calculate the amount of compensation needed for each string. A unique nut and saddle must next be crafted to fit these calculations. Once manufactured the nut and saddle are not adjustable and must be replaced if alterations are necessary. Your results may vary and predictions from the model may or may not match the realities of the actual instrument.
There are a variety of ways to look at the data and extract useful information. Right now we have two objectives in this analysis. First, we would like to have a systematic method to optimize the intonation on an individual guitar, and second we would like to have a simple set of metrics that allows us to objectively compare two guitars or monitor the progress of an individual guitar as it is intonated.
Linear Equation Best Fit to Data: When we apply a linear least square fit (an Excel linear trend line) to a set of data we generate an equation that tells us the slope of the line and its Y-intercept, see Fig 9 for an example. These parameters directly correlate to the adjustments we have at the bridge and nut. The slope of the line is controlled by the position of the bridge saddle. If the slope is positive, the notes are getting sharp as they are played up the fretboard and the bridge saddle is too close to the nut. If the slope is negative the notes start to play flat and the bridge saddle is too far from the nut.
The second parameter we consider from the linear best fit equation is the Y-intercept. We can control this parameter by adjusting the nut saddle position. If the Y-intercept is negative, the intonation is flat and the nut is too close to the bridge. If the Y-intercept is positive the intonation is sharp and the nut is too far from the bridge.
Linear Plots and Body Resonances: When a note is played the top of the guitar vibrates and interacts with the vibrating string. This top resonance interacts with the vibrating string causing the string to play sharp if the top resonance is flat of the string resonance, flat if the resonance is sharp, and causes the note to split in two if the resonance is right on the string frequency. If this is happening and the signal is sufficiently strong, this phenomenon should present itself as a consistently flat set of notes that slowly transition to consistently sharp as they are played up the string. Figure 10 shows a plot where this might be happening around the G#... maybe.
Dot plots to investigate note compatibility: One of the desirable aspects of a pretty well intonated guitar is playing two notes on two strings at the same time and they play in tune. By changing the chart type from a line plot that emphasizes the relationship of notes on a single string to a scatter plot which removes that emphasis, we can easily see the relationship of equal notes on different strings. Figure 11 shows a plot where data points in a vertical line are equivalent notes and the distance between them is a measure of the frequency equivalence. For visual clarity the horizontal axis is the natural log of the frequency.
Displaced Dot Plots to Look for Fret Position Errors. Figure 12 is created by offsetting the scatter plots so that notes that are played on a single fret are now shown in a vertical line. By examining the data point placements it should be possible to see systematic fret placement errors. If the note errors drift systematically from sharp to flat or visa-versa it may be caused by a fret placed at an angle. If a single note or set of adjacent notes are sharp or flat, it may be possible that the fret is miss crowned. If all of the notes play sharp or flat it may be possible that the fret is misplaced or the crown is off center.
Reduced Plot Playing Area (Practical Playing Area): It may be desirable to optimize the intonation over the set of notes most likely to be played. Figure 13 shows a plot where the highest notes on the lowest strings have been ignored and not plotted. These are notes that are least likely to be played. With a reduced number of notes it will be easier to get the intonation right.
Statistics: The following are a set of statistics that help describe the distribution of errors. We can use these to compare different instruments, or to follow the progress of intonation improvement as we set up a guitar.
Mean: commonly called the average.
Median: the number where half the population is above and half below.
Standard Deviation: a measure of the spread in the data.
Kurtosis: a measure of how much data is in the wings of the distribution.
Intonation Quality Q=Frequency/Delta-Frequency = 100/(RMS Percent Errors)
The quality of an acoustic instrument has many elements with the sound it makes one of the most important. Intonation or how well it is in tune is a major component of sound quality. Needless to say, a well-tuned guitar sounds better than one out of tune. To enable our efforts I have develop a set of technologies and a system that is compatible with an acoustic guitar. The Portland Guitar Pretty Good (PGPG) Intonation System works Pretty Good, not perfectly, but pretty good. The basic physics and mathematics of the system is well known and has been for a very long time. This new system is flexible and adaptable and can be changed as the guitar matures and changes. The system should be applicable to other stringed instruments. The real opportunity here is crafting a new class of instruments that raise the level of quality by several factors, but a rearguard action can be taken to retrofit instruments already made.
Although not trivial to manufacture, the components for the system are straightforward, simple and intuitive. If getting to perfection is an admirable but fool’s errand it comes at the price of manufacture complexity, setup and maintenance, or else simplicity. The PGPG Intonation system works well for this purpose. It is easy to build if you have the right tools, is mostly intuitive, addresses intonation in-situ and respects the guitargeist of the instrument. But, it is much more complex than a straight line bone saddle and nut which works well enough for the majority of instruments. Using this system should help when the errors of the standard systems are not acceptable. If it has to be as right as possible however, this may be a way to get there. When the setup and maintenance steps are an acceptable burden then the results of this system may well be worthwhile. On the other hand, perhaps it is time we finally hear our guitars in tune. Even given the increased complexity of the PGPG system, so far it seems to be stable and robust and easy to implement. Only patience will tell if it will stand the test of time… or is that the test of tune… we shall see. My hope is that this system helps us enhance and enjoy the beautiful sounds these wonderful instruments make.
An Amusing Anecdote
When I was developing this technique I had finally put everything together and tuned up my new guitar. I then started to apply the PGPG intonation process and watched the graphs converge on the zero line. I kept working at it and started to get frustrated with the variation. I poked and prodded and re-measured every note a dozen times. I finally gave up and said that this is as good I can do I guess. I thought to myself that this works, but only to a degree. Then a brilliant idea, let’s check another guitar. So I grabbed my guitar from another brand since if I had to face the music as, it were, this was the guitar to compare. I started to go through the process and got the first results. I finished up and looked at the graph and compared it to my new guitar and then went back and forth. Hmmm, maybe I’m on to something here. I promptly stopped working on my guitar and celebrated… Hazzah!
What’s Next, Follow-On Research and Development
Make measurements easier: One has to admit that measuring every note on the guitar several times is a tedious, boring time consuming process. It would be desirable to find a proxy for a full set of measurements, that is, what is the minimum number of measurements that need to be taken to get the same results as when a full set of measurements is used.
Reduce measurement error: Presently measurement error seems to be the limiting factor to improving the results. If we can increase the signal to noise level of the intonation measurements we should reveal the individual errors that the frets are introducing, and perhaps the resonance interaction will become more apparent. The fact that the notes pitch follows a trajectory that takes it from sharp to flat to sharp to whatever as it loses energy is a particular problem. To improve accuracy there are at least two paths to follow. One is to use a spectrograph to record the data. This increases the complexity of the measurement and can increase the time required for each measurement depending on precision. The results from a spectrograph are high quality and the method is worth pursuing although cost is prohibitive. The second path to pursue is to develop a transducer that can be lightly coupled to the strings. By using a high precision audio generator we can fret each note on the fretboard and then tune the generator to excite the fundamental of the string. This method has the advantage that the measurement is made at a steady state condition and should eliminate frequency wander. The disadvantage is that the coupling between the transducer and the string may alter the resonance slightly. This would need to be investigated.
A lot can be learned about the intonation characteristics of guitars by conducting a survey of instruments. What we don’t know is what we don’t know and it would be nice to shed some light on the subject. I would like to measure as many guitars I can get access to. It will be important to examine the gamut of instruments form off the shelf to custom high performance guitars so that we can see what works and what doesn’t.
Continue to develop the adjustable nuts into more elegant a sophisticated designs.
Spread the word about this new development.
And finally and most important, build more guitars.
Check out the more about the adjustable neck
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As delivered the bottom of the bridge blank is flat. The depth of the blank may be deeper than necessary. The wings are left for you to finish with your own design. If your guitar has a domed top the bottom will need to be shaped to fit.
The depth of the blank can be set by sanding the bottom. The specific depth will depend on the particular design of your guitar. We’ve had success using the same depth as a standard bridge. When sanding, remove the bottom evenly.
To match the bottom of the bridge to the top of the guitar: use double stick tape to adhere an 8.5” x 11” inch sheet of 100 grit sandpaper, grit side up, to the top of your guitar centered on the planned position of the bridge. Next, mark the bottom of the bridge blank with a pencil so that all areas are covered. Gently sand the bottom of the bridge blank centering your strokes on the proposed bridge position. Continue this until all of the pencil marks on the bottom of the bridge blank are gone. While sanding be careful to not press down too hard, it will deform the top of the guitar. Be careful to avoid rocking the saddle blank back and forth while sanding it will dome the bottom of the bridge.
Use your favorite technique to shape the wings. Be careful to leave enough depth.
The bridge can now be attached to the top of the guitar. Use your favorite glue. The adjustable saddles make the position of the bridge forgiving. We have had success positioning the bridge so that the forward position of the saddles is 0.125” farther back than the desired scale length. For example, if your desired scale length is 25.400” position the front of the saddle channel 25.525” from the nut (25.400” + 0.125”). Orient the bridge so that it’s perpendicular to the centerline of the strings.
Each string can now be compensated. Tune the string to its desired open note. Then play the note at the twelfth fret. The second note should be exactly one octave above the first. If the second note is sharp of the first, use the adjuster tool to move the saddle away from the nut a small amount. If it is flat use the adjuster tool to move the saddle closer. Continue until the two notes are perfectly in tune. Repeat this for all the strings.
The height of the saddle can be changed by adding a shim under the saddle in the saddle channel. This can be used to contour the top of the saddles to match the contour of the fretboard.
Each guitar is unique. The saddle positions may end up not looking like a standard compensated bridge. Further, each gauge of string has its own unique compensation.
To avoid misplacing the position of the saddles when the strings are changed, it’s held gently in place with a small spring. The saddle should stay in position without the string in place, and it should be able to be move with the string at tension. Though the saddle plates are not held in, take care to not lose them.
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