Official Luthiers Forum!

Hi Folks,
Thank you for your interest and kind comments about my fingerboard radius jig. And much thanks to JJ for completing it so nicely. The square piece of UHMW on the router base is a great idea and will stabilize the travel of the router.

I had been trying to come up with an easy fixture to use with my thickness sander, some kind of carriage thing. I wasn’t too successful though. While on a walk with my wife and dogs I was discussing the design problem (let’s hear it for wives who put up with boring construction stuff!) and she said why not just use your router.

So I came up with this 3-sided box with a carriage that travels laterally from the fingerboard and follows whatever radius is under it. I have made compound radii from 12” to 24” and it works fine.

It’s easy to make and I tried to document it in a way that is easy to follow. One of my favorite features is you can shape the top rails to include the parabolic relief required for really good action. Of course, after the FB is glued to the neck some fine-tuning is required. Thanks!

Rick Micheletti
Luthier’s CoolTools

Welcome, Rick...thanks for chiming in. I hope you decide to be a regular participant...we always appreciate someone with your stripes! Full disclosure...I invited Rick to this thread to answer the questions we all might have on the design and function of the jig.

I have a couple of questions to start:

1) Guide blocks...I know they're supposed to float up and down but I had better success when I actually clamped them down on the short side of the slot. They have a tight fit in the carrier and prevent lateral movement but the carrier seemed to stay in position better when I used the clamps. The positive stop for router travel was a bonus.

2) Router bit...What effect would a flat-bottomed bit have on the quality of the radius instead of the recommended core box bit?

3) Carriage bolts...How tight should the tension be on the carrier? I cranked them almost until the springs were fully compressed.

4) Router direction...I went longitudinally but was wondering if it might be better to take a second pass with the router stationary and moving the carrier laterally. Is there any merit to this? Any down-side?

5) Other applications...It seems to me that this could be used to thickness fretboards, bridge blanks, head plates, etc. for those of us who don't have planers or thickness sanders. Seems like all one would need is to substitute are 0-radius inserts. Have you had any experience with such applications?

TIA

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JJ
Napa, CA
http://www.DonohueGuitars.com

John,

I use Kaman, there is probably one in Victoria, or BC Bearing. What about Capital Iron? They have a lot of this kind of stuff as well.

Shane

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Canada

Another question for Rick:
It seems to me that height adjustment of the templates is critical, especially if you are trying to do compound radius boards. Any unintended taper in a board is obvious.
Do you just shim the templates with veneer and tape to get the height 'just right'?
Thanks
John

Welcome Rick!

For all of you who don't know, Rick is the gentleman who sells the Fleishmann/Williams binding jig plans on eBay also. I have a set of these fretboard radiussing jig plans and will probably build one. I realize once I've built my cnc, it will be defunct, but for now it's a good looking tool. A vacuum hold-down would be a great modification for it. I may try that...

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

John...The templates provided for fabricating the radius blocks are taller for the higher radii.

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JJ
Napa, CA
http://www.DonohueGuitars.com

Thanks for all the answers and hints in response to my questions.
John

JJ: where do you place the clamps? Simply on the guide blocks, ocer the carrier board, clamping onto the base of the 'box' itself?

I was thinking you could even extend the guide block bits out, add 2-4 heavy duty springs per block (externally, although small indentations in the carrier board on the inside of the main box and you could put them internally). I'd still be curious how smoothly it all moves along an 'extreme' compound radius (10-24), given it will want to displace longitudinally (otherwise, you'd need the baseboard to twist, or the bearings wouldn'y make solid contact). Mind trying it out for me? Not routing, just shifting the board itself over two different radius rails...

Mattia...The sides are referred to as "near side" and "far side". The two 1/2" slots in which the guide blocks ride are 1.50" deep on the far side and 1.25" deep on the near side. I simply put a clamp at the 1.25" side such that the guide block bottoms out in the shallower slot. I wouldn't make it any more complicated than that.

I have not made up any more radius blocks (only 16" and 0) yet. I'll make up a pair of 12's and 24's this weekend and do as you request to determine the effectiveness of the carrier travel at the extreme. Stay tuned!

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JJ
Napa, CA
http://www.DonohueGuitars.com

JJ - I’ll try to answer your q’s

1)     Guiding the carriage perpendicular is maybe the most difficult part of making this fixture. There’s probably a better idea staring us in the face. The problem is things get a lot more complex and expensive, for example a linear bearing guide.
2)     My core box bit has about ?” flat in the middle. I don’t remember where I bought it – try a flat bottom bit on a mock fb & see how it works.
3)     I wonder if I spec’ed out the correct springs…should be .060” compression spring. I have my wing nuts cranked down about an inch on the carriage bolts, enough to put some tension on the carriage and still be able to move it smoothly.
4)     I think router travel should be longitudinal – maybe a different router bit could help for fewer passes.
5)     Haven’t tried that idea – sounds like an easy way to flatten things for those without more expensive equipment. Many classical and flamenco builders like to taper the bass side of the FB and others taper the entire board. This tool would be perfect for that, just slip the appropriate shim under the radius guide or make a more permanent one.
- for those who do not want taper in the fb, it is critical to ‘zero out’ both ends of the router bit to the fb. I have attempted to compensate for this by making the tighter radius blocks taller than the flatter ones (yea AutoCAD) but some adjustment may be necessary in the way of shims or removing some material under the blocks - R

bump

Mattia...I felt the bump! Thanks for the reminder.

I must apologize for not getting the answer to your question on the compound radius trial. I got a bit distracted over the weekend with the guitar crash, trying to move 3 guitars down the assembly line and some domestic issues.

I need to fashion the 24" radius blocks and just do it. Sould be able to do that in a day or so.

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JJ
Napa, CA
http://www.DonohueGuitars.com

No rush, just keeping things alive! With the arm situation, it's not like I'll be building anything any time soon...

Update...I just got an email from Rick revising his plans as folows:

"The router bit used for this fixture should be a “bowl & tray” bit, ?”. This is made by CMT, part #851.002.11 and is available at routerbitworld.com."

Anybody need a 3/4" Core Box Bit?

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JJ
Napa, CA
http://www.DonohueGuitars.com

Mattia...Here's the scoop on the 16" to 24" compound radius setup. I made up the 24" block and set it in place with the 16". I measured the clearance along the length of the carrier board and it's consistent from end to end. While I don't have the time to do an actual FB I'm fairly certain that it can be done effectively. Check it out:



It should work fine for your electric FB's.

Good luck and take care of the arm!

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JJ
Napa, CA
http://www.DonohueGuitars.com

Bump so Mattia can see it!

JJ: thanks a bunch!