A while back, several of us were discussing the Yonico radiusing bits. They are available for all common radii. I purchased mine here:
https://www.precisionbits.com/guitar-fr ... 13003.html
The question was how the heck to use these. The consensus - with which I agreed - was that the proper way to use them was in conjunction with a router table and fence. Using them hand-held and/or relying on the guide bearing seemed to be a recipe for disaster. It turns out we were correct, and here is how I made this work.
Big Caveat Here Folks!
I tried to use this setup on my last build. The biggest limitation of this method is that it seems it can NOT be used on a FB that has been routed for inlays. I made several test fretboards with a couple of inlay recesses routed into it, and no matter what I did, no matter how light a pass I made, the bit seemed to want to take a shallow divot out of the FB at the inlay recesses, even when it appeared that the guide bearing was NOT riding on the FB. I know this doesn't make sense, but I tired of making fretboards and routing inlay recesses to try to figure it out, and went back to hand-planing and sanding on the last build.
IF on the other hand, you are using dots or routing for inlays after radiusing, then this seems to work great.
The goal of the jig was to be able to affix a FB to it, run it across the bit in several shallow passes to radius one side of the FB, then flip the mounting over with the FB still attached, and make several passes across the bit to do the opposite side. This required that the FB would remain square to the bit/table and the centerline would remain parallel to the table in the process of making the flip.
I started by making a base from two pieces of aluminum angle. I don't have a TIG welder, so I glued the two pieces together using JB Weld. The assembly would subsequently be screwed to a wood block (seen below) so it isn't relying solely on the adhesive. The backing wood block was shaped to allow mounting of a couple of "handles" I had in the rat hole, and drilled for a simple threaded-rod-and-four-spoke-knob mounting.
I faced the bottom of the angle - where it will rest against the top of the router table - with UHMW tape.
In this picture you can start to see the real magic of this jig. The face, on which I attach the FB with double-sided tape, is made from a 1" thick piece of cherry well impregnated with epoxy to both stabilize the wood and to provide a surface from which the tape can be easily removed (later replaced with MDF - see below). Note the two threaded inserts for the mounting bolt in the center. There are two to allow mounting when the mounting face is flipped end-for-end. Note also that there are four 1/4-20 set screws on the back of the mounting face. This allows the face to be adjusted so that it remains vertical when flipped. They are positioned so that together with the mounting bolt they create a three-point contact between the mounting face and the aluminum angle.
On the ends of the mounting face, I drilled holes at an angle and threaded for four additional 1/4-20 set screws on the top and bottom edges. This allows the mounting face to be adjusted so the centerline remains parallel to the table surface when flipped end-for-end.
- I should mention that I drill and tap wood/MDF all the time for set screws and other adjusters and mounting. A fine-grained wood like cherry or maple can be threaded very easily and the threads hold amazingly well. I've seen some engineering testing of how well threads hold in wood, and practically speaking for the purposes of jigs and fixtures it's as good as metal. Threads can easily be reinforced to withstand repeated assembly and disassembly by soaking the threads with CA glue or epoxy, then chasing the threads again after the resin has set. A bit of beeswax makes the screws work very smoothly.
Also, note that in later pictures I switched to epoxy-stabilized MDF for this mounting face, as despite my best efforts, the cherry DID warp over time. MDF also really soaks up the epoxy so the threads hold and hold up very well. Everything else remains the same.
Here is a view from the back of the jig. Note the handles that allow me to press the jig firmly against the table and the fence while keeping my hands away from the twirly parts. The four-spoke knob is loosened, the mounting face is flipped end-for-end, and re-attached to do both sides of the FB.
See the next post for the last three pictures (we still seem to have a 5-picture limit).
The last three pics show the fence setup. I use a straightedge to eyeball how far the guide bearing is back from the face of the fence. The next pic shows using a height gauge to ensure that the router bit is set to the correct height. The test piece at the end shows that I had that dialled in perfectly. The actual FB ended up with just a bit of a flat spot in the center, easily sanded out with a few strokes from a radius sanding block.
So, bottom line is that if you have something substantial to hold the FB while run across the fence, these router bits seem to work really nicely. I understand that some have successfully used a router to radius a FB in which MOP inlays have already been glued. If I was more ambitious I'd give this a try, but I'll leave it to someone else to explore that!