Every job in the CNC starts with the design process. Sometimes it takes hours and sometimes days. For creative designs, the ideas percolate for weeks.
There are two major tool paths used to create the fretboard, a radiused profiling and the fret slots. First the radius is put in. This is done with a ball end bit
A channel is routed for the white border then glued in.
Then the slots are routed.
The pigment is applied after the fretboard markers are routed. Channels for the inlay are also done. This was one of the first times. A cyanoacrylate with the green powder proved insufficient. Too many cracks and uneven fills. The process later changed to adding the pigment to an epoxy resin.
Six fretboards were created this round. The goal was to get it close to perfect. During steps like these, it’s easy to repeat most of the work, it’s possible to retry a few times. This was one of the early and unsuccessful trials.
There are lots of cracks in the inlay and uneven edges on the binding. It wasn’t right so another was made. On the third trial it started to work. Here is the epoxy painted on.
Drying overnight.
Time to put in the frets. CNC is used to make 20 blocks of differing radius, used to press in the frets. It gives an even fit and minimizes the amount of work needed later.
Three stages
The tang of the frets needs to be ground down so they don’t stick into the binding. They are put in this holding device then sanded off.
This batch is complete. It turned out nice in my opinion. Here are three.
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Here are the last pictures to catch up.
Laying the glue down on the curfing. A liberal amount is applied to make sure all
the edges are filled.
Scraping squeeze out from the inside of the body. No one will see this, but it’s important for the spirit of the instrument.
We’re installing K&K pure mini pickups on this batch. They have three contact pads that go underneath the bridge.
The four bodies completed
Frames, braces, tops, backs and glue create the bodies of these guitars. The braces and frames are complete, onto the tops. The same style and design will be used for each one. An amboyna burl rosette with a black white black border. First a little work to complete the frame.
A bottom decoration is put in to hide the joining line. The inlay and wood insert are glued in. It’s a messy process.
It’s cleaned up with a chisel and sandpaper.
Next, we turn to the top and the rosette.
Channels are routed in the cnc then inlay is glued to the outer and inner edge. Pressure is applied and a drop of glue seals the deal.
The pieces of the rosette are routed out. To conserve space the circle is broken up into four quarters. They are tessellated in a rectangle then cut out. Double stick tape keeps them attached to a spoiler board. To be detached, heat is applied.
Glued in place. Some adjustment required.
The finished product on spruce and cedar
A large detour to create elegant purfling ensued. Many ideas swirled for this series. The wave designs worked well for the last series. A good design, but a now comfortable technique. A new purfling pattern is desired for this set. Nature and symmetry inspire the set.
Technical difficulties present the next challenge. The idea is to make long thin strips using the bandsaw. Then cnc the pattern.
It can make any pattern it’s given. But different router bits used will affect the size and resolution of the image. Purlfing is not wide and looks better when in thinner strips. To accomplish this precision a 0.05” end mill bit is used.
Small strips mean small details. Thin purfling and patterns want to break off and ruin the run.
The strips bend around the lower and upper bouts. This provides a limit on the thickness in certain places.
Here is the cnc at work. The wood used for the first trial was bog wood. It’s light, hard to see in this picture. It’s taped down to a spoiler board. An added problem is that the purfling can break while being pulled up.
Using the heatgun and a scraper the pieces are pried up.
One of the designs that worked.
Another design that worked.
There was limited success making these. The key design snapped in multiple places many times.
The number of strips that were usable ran out and attention was turned to finishing the bodies once again.
The back was sanded in places.
A set of back and sides were finished and glued together.
The body glued together.
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Wood bending has two main components: heat and water. These serve to loosen the ligands in the wood and makes them more pliable. When bending sides there is continuous heat that is added at the same time as the water. The water serves to distribute the heat and make sure that every part of the wood is hot. The water absorbs into the fibers and acts as a lubricate between the fibers allowing them to move more freely. The amount of water vs heat needed various.
The strips of wood are soaked in water. The water can be warm but it’s going to cool down over the time that it’s soaking. This step isn’t to add any heat to the wood it’s only to make the water absorb through the wood. It’s left in the sink for about thirty minutes. 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 thirty minutes are 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 only 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 side, a notorious bend.
The wood is clamped into the jig and put in the oven.
Here’s Jay taking the braces out. It’s hot! Those clamps absorbed a lot of heat.
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hey are left to cool down and hold into the form. It would be a problem to release them from the jig now and have them relax back to a flatter position.
The carbon fiber is rolled out and taped off in sections. This helps keep the end strands together when cutting it out.
A piece of wax paper is placed on top of the form, so the epoxy doesn’t glue the braces into the form.
Glued together.
The braces are cut out on the band saw and then placed on the top in a pleasing shape.
They are glued in using the go box. Glue is sticky and slick at the same time, so it takes some care to fit the braces in while pressing down on them.
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This round is another set of Brazilian rosewood guitars. We recently bought a few more sets of this so the time to build with it is now. There are going to be two 14” bodies and two 16” bodies. As well there are two tops, Adirondack spruce and western red cedar. These combinations make four guitars. Here are pictures of those woods. The tops are already joined and the rosette channels are routed.
The neck blanks as well have been completed
Next is the sides, here they are bent with curfing on
The blocks need to be glued in to hold the two pieces together
Observing his work
The edges must be sanded
A stack of frames
Now it’s time for the fun activity of cleaning out the shop. So much wood dust.
These are going to be some great guitars. I’m excited to see and hear what they will be like.