CNC Set Up
Section_ Ebony Fretboard Stock
CNC finished contour radius before final sanding
The reason that I invested in a CNC machine was not to do things faster but to do things better. Inlay was my final motivation.
Woody has a few ideas that might be interesting and attractive if well executed as pearl or abalone inlays. We would certainly not be the first. The challenge is the "well executed" part. With the CNC, the development and execution of a design is in creating and drawing toolpaths with the software. Then there is the physical set up of the machine knowing that major damage can be done if the bit doesn't go where expected. That's all on you. The machine doesn't make mistakes. It only does what it's been programmed and set up to do. A perfectly good fretboard can be ruined as easily as it can be made creatively interesting.
The first challenge is to design an inlay in coordination with the tools (bits) that you have to cut it. For example, sharp corners in your design may not be as crisp as you would like if the bit is too big. Pocket corner radius is limited to the radius of the router bit. It might take a couple of tool changes to sharpen the pocket profile. Below is an example.
Software image of Contour Radius and Inlay Pockets with the CNC
...yes, Alaska. See "Becoming a Luthier" above.
November was a month of continued learning on the CNC. There's an endless number of techniques to learn... and remember.
Explained this month (as with last month) will be some of the 'How To' that make Computer Numeric Control (CNC) challenging and, when it's right, very satisfying.
Below, Woody has tried to explain a little bit about getting started with the CNC software. Some cautions will be offered in regard to machine set up for guitar making processes like inlay, fretboard radius and the like.
Hopefully, this will be interesting in a different sort of way from straight luthiery although, for my purposes, it is just another luthiery skill to be learned.
This is the machine that I use. As CNC machines go, it is not that expensive (3k). It's called a Shark II (aka HD-4) made by Next Wave and it's about as small a CNC as one can get. Still, it's a bit too heavy for delicate luthiery work. Nonetheless, it works quite well and it's very well made.
One of the beauties of this machine is that it will fit in a small space. Woody has this one set up in an un-used bedroom downstairs.
Below is pictured the 'shower-curtain' method of keeping the quickly-accumulating dust and wood chips in a confined area. A yard-sale vaccuum cleaner (not shown) has been modified to handle cleanup duties when the chips pile up. Whatever the set up, be sure to keep the controller outside the dust area.
As always, the methods described here are for the Home Shop luthier. Both supply and return ventilation to this room have been blocked.
Pictured above is what I call a 'paisley' that I use for fretboard position markers. It is approximately 6.5 mm tall (~1/4"), and 16 mm wide (~5/8"). Below is pictured the paisley profile with the path of a 1/8" bit for hogging out most of the paisley posket. All works well until the tip of the tail (on the right) narrows down to a diameter less than 1/8" (0.125").
For the tip of the tail we have to change bits to 0.035" diameter as pictured on the right along with the 1/8" bit profile. Every bit change requires the operator to manually re-zero the Z plane. Caution: mistakes can be made every time one manually changes the zero in any plane. Broken bits are not uncommon when learning to manually set up and drive the router. At $25+ per bit one learns quickly. It still happens. Adjust your budget accordingly.
Next month we will talk about cutting the fret slots and profile of the fretboard. Then there are some ideas about headstock and rosette ideas that I hope that you will find useful. Woody will be happy to answer questions (if he can).
Until then...be careful, work scant and remember it's just wood and strings.
P.S. Christmas is between now and next month. I hate to say it but I don't usually get much done in the shop in December. Send more your questions... then I will be busy.
Facet Creation with Thickness Sander
As I get older, I find the muscles in my shoulders down to my fingers get tired from pushing sanding blocks. For years I have sanded the surface of my fretboards to achieve a 12" or 16" radius. After rough surfacing on a thickness sander, facets remains that need to be sanded smooth as the surface is contoured into a radius.
Contour the Fretboard
Using the Moulding Toolpath in the software, two vectors are required. The first vector is called the Drive Rail (the length of the contoured area). In our case the drive rail vector is the a line drawn down the edge of the fretboard and parallel to the center line. The profile vector is an arc of 12" radius (or whatever fretboard radius you are using). The length of the arc should be the width of the fretboard stock. In my case about 75 mm.
Once these two vectors are created, open the Moulding Toolpath and select the drive rail then select the contour profile. The last vector selected will be used as the contour profile. The contour will be cut across the fretboard stock and along the length of the drive rail. A 1/4" ball nose bit with 7-10% stepover will produce a smooth, nearly finished contour.
Rough Fretboard Radius on a Thickness Sander
It's a good idea to practice all of your toolpaths on styrofoam. Then replace the foam with ebony and repeat.