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Radius Router Bits

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OK, so I had these router bits custom made for me by a machine shop contact, to the tune of $200/ea. I'd got a bunch of quotes from commercial manufacturers that were all in the $265 to $315 each, so I think I got a good deal in that respect. They are a bit pricey but because I am finding my free time is not what it used to be, I am reveling in the fact that I can now radius a fretboard in ~5 minutes.


Here's the tutorial for those who asked.

1) These are used in a router table (mine's a fairly cheap Craftsman), I'd never use them in a hand-held. The bearing runs more or less along the centerline of the fretboard blank. First bit of business is to plane square and true a block of wood longer & wider than the fretboard, so that you can mount the fretboard centered on one side and not have the edge of the board touch the router table. I used a 4x4 mailbox post for this, planed & squared up on the jointer. Fingerboard blank has already been planed flat by this point; the board pictured is a birdseye maple fanned-fret board with integral binding, slotted but not yet tapered.


2) I'm using the 16" radius bit for this board. I raise the bit so that the lower edge of the bearing is on the centerline, then make two passes, flip and make another 2 passes. Normally this does the job on the outer half of the board, you can see there's a strip down the center that hasn't been radiused yet, and this is clearly shown by the radius gauge.



3) Now iterate...raise the bit, make a pass, flip and make another pass, keep raising the bit a little at a time until you just eliminate your centerline on the board. This leaves a subtle ridge down the center of the board that is ever so slightly high, easily knocked down with ~10 strokes from a sanding block (I used a radius block I already had on hand).



The result is a radiused board with a precise uniform radius that is even across its width...no more fretboard with assymetrical radius!


The surface here is very nice. This was a board that I got a fair bit of tear-out from the jointer, so I had to use a drum sander to bring it to proper thickness. I got no tear-out at all with the radius bit, even though the board was already slotted. Here's a shot of the finished product, after knocking down the center ridge.



Edited by erikbojerik
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Hi Erik that is a very cool idea and a very accurate way to do this, I would love to have a set of these "BUT" the price of each individual cutter that I need would be almost $1200+ dollars and for that I would invest in a belt sander and make a swinging radius adaptation which would be more than I would ever need and I know the accuracy would be perfect. If there was a group buy and these were made at a more affordable price then I would be certainly in for sure 100%. I'm sure others would probably feel the same ?? great idea bro.

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Sorry a bit OT, but I have to say that I love the fanned frets! I play a Dingwall ABII & am contemplating building a fanned fret guitar. How did you calculate the placement and angles?

Thanks for the tutorial -- like everyone else, I think it sounds like a great, if not pricey, option.

-DC Ross

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More OT talk about fanned frets:

I would imagine you just have to figure the fret positions based on the scale of the lowest string and the fret positions based on the scale of the highest string, and connect the dots.

And I was just thinking about bends on fanned frets. Seems like it would only really work when bending toward the bass side of the fretboard...?

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OT Fanned Fret talk, continued: that's my understanding, too, and fits my sense of logic (the 2 scale lengths and then connecting the dots). As for "working", fanned frets aren't to facilitate bending, Rick-- but rather to accomodate scale length needs as well as a (debatably, since not one size fits all) ergonomic layout for fretting.

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