# Fingerboard sanding block radius fixture



## difalkner (Jan 3, 2012)

That's a long title but, for those of you not aware, a guitar fingerboard is typically not flat but has a radius (except classical guitars and those are most often completely flat). Electric guitars typically have a smaller radius fingerboard and acoustic guitars have a slightly larger radius. 

So how do you get that radius? Most people just sand the radius because it's a slight amount. Some people use a flat block and sand until it 'feels' right, others rig up something to use a router or sander, but I have feeling most people use a defined radius block with sandpaper attached. That way you know that if you want a 12" radius then your fingerboard will end up with exactly that radius.

I am at the point in my build where I need to radius the fingerboard but I don't want to spend $20 for a sanding block or $75 for a set of five blocks, especially since the set at StewMac only has one block I would use, the rest are too small. And since I plan on building a lot of guitars and figure I will get requests for all sorts of radii for fingerboards then another fixture was in order. Btw, I don't really build guitars... I only build fixtures, or so it seems.

This is an idea gleaned from YouTube, so this isn't completely original. Some facets of it are but basically I saw a few things I liked and just winged it from scraps yesterday. Now I can cut any radius I want and make the blocks as long or short as I desire.

You'll note the pivot point is the exact distance to the end of the router bit so I have marked 12" to 20" in one inch increments. For this build I plan on doing a conical radius, often called compound or multi-radius, and it will be 14" at the nut (headstock end) and slowly transition to 18" somewhere in the middle on to the soundhole end. 

To use the fixture the block is pushed from front to back going under the bit, then turn the crank about half a turn and run it through again. After a couple of minutes there is a constant radius arc cut into the block. I will glue sandpaper to the block and use that side to sand the fingerboard to the desired radius. Simple, really. And it took a lot longer to type all this than it does to cut one block, fwiw.

Fingerboard sanding block fixture - 
















Adjustment mechanism - 








Pivot hole increment marks - 








14" and 18" radius sanding blocks -


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## RainMan 2.0 (May 6, 2014)

Great outcome . Nice job Dave 

It seems there's not much that can't be done with a router with the right jig system.


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## Cherryville Chuck (Sep 28, 2010)

Nice job Dave. You can use the same basic idea to rout the finger board instead by mounting the the board at the end of the pendulum and leaving the router fixed.

One other option I might consider would be making a set of scrapers for different radii.


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## difalkner (Jan 3, 2012)

Cherryville Chuck said:


> Nice job Dave. You can use the same basic idea to rout the finger board instead by mounting the the board at the end of the pendulum and leaving the router fixed.
> 
> One other option I might consider would be making a set of scrapers for different radii.


Thanks, Chuck! I actually thought about that but figured I would 'sneak' up on the radius by sanding. That and I plan to do the conical radius of 14" transitioning to 18" and that's going to be easier with sanding blocks.


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## difalkner (Jan 3, 2012)

Had a few minutes this morning so I put a little video up on YouTube showing the fixture in operation -


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## Cherryville Chuck (Sep 28, 2010)

If you install a compression spring on the handle shafts it might be able to hold itself in position.


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## difalkner (Jan 3, 2012)

Cherryville Chuck said:


> If you install a compression spring on the handle shafts it might be able to hold itself in position.


You noticed that, huh? LOL! I guess I made it operate a little too smoothly and actually thought about a spring. But it served its purpose for about 10 minutes of sanding block making and is now hanging up on my French Cleat waiting for the time I need a different radius or decide to make some out of Maple. And I'll probably do just as you suggest and add a spring at that time. Thanks, Chuck!


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