Making a 10" radius sanding block

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CrealBilly

CrealBilly

New User
Jeff
I needed a 10" radius sanding block to radius the finger board on the bass guitar I'm making. The finger board radius must be the same at the nut and bridge or the guitar will not play correctly. The last guitar I made was at my buddies in northern IL and he had a set of store bought - 8" long wooden blocks. Instead of popping $15.95 plus SH and time it takes for UPS to deliver for a 10" diameter sanding block. I decided to venture out to the shop and make a 10" radius sanding block.

After thinking about it for a while, it dawned on me I have a 10" tablesaw :). So I squared up a length of 2x4 poplar and clamped two parallel 1x4's to the table saw at about I'm guessing 30 degrees with the center of the blade. With the blade just barely rasied above the table, I very carefully and gingerly pushed the length of 2x4 through the sawblade. Like magic it worked there was a slight radius in the middle of my block, no kickback and when through fairly smooth. I thought awesome :) so I continued to raise the blade a little at a time till my radius was 2 1/2" wide. The radius looked awful small to me, way less than 10", so I checked it and I was right... it wasn't 10" :(

I pulled the blade off the table saw and measured it sure enough it was 10"... uggg... what did I do wrong? 10" is 10", isn't it? uggg... :(

Then it occured to me :widea: what if I push the block parallel to the blade, 10" is 10" it should be right. So I used my square and lined up the 1x4's exactly 90 degrees to the miter slots and and the center of the blade and tried it again with another length of squared up poplar 2x4. Low and behold it worked, dead on 10" diameter :) So I cut the block to 11" long and fastened a full sheet of sand paper with some push pins to the sides of the block and started sanding. It worked like a champ, I couldn't have been any happier, now I have a 11" long block instead of 8", that's just as good if not better than store bought :)

Pic of my 1st attempt at what I'm guessing to be around 30 degrees - most importantly it's not a 10" diameter.
P10100872.JPG


My 2nd attempt at 90 degrees to the saw blade - dead on 10" radius.
P10100881.JPG


Now I have a question, for those into solving mathematical story problems. Does anyone know the formula for the radius produced from a given saw blade diameter at various angles?

Thanks
 
B

Ben325e

New User
Ben
Am I the only one bothered that this 10" radius is only a 5" radius? If it were just for looks, that's one thing, but it's the fret board of a guitar - too much curvature will make it uncomfortable and unnatural to play, right? I'm not a guitar player by any means, though.
 
Tarhead

Tarhead

Mark
Corporate Member
I agree Ben. It's a 5" radius and way too severe for a fretboard.

Jeff,
Find a piece of 20" cement drainage culvert and put a piece of wax paper on it. Mix up some Bondo and apply it about 1" thick to an 8" X 4" piece of 3/4 plywood. Slap the board Bondo side down on the wax paper and let it set up. Trim it up and put some PSA sandpaper on it.

Credit for this goes to Charles Neil who has a video on his site showing how to make sanding profiles for molding.
 
eyekode

eyekode

New User
Salem
I think your best bet is a router with a circle cutting jig. Laminate extra pieces an use a flush trim bit for the pieces you glue on.

Routers are great at making perfect circles :).
Salem
 
ehpoole

ehpoole

Moderator
Ethan
eyekode said:
I think your best bet is a router with a circle cutting jig. Laminate extra pieces an use a flush trim bit for the pieces you glue on.

Routers are great at making perfect circles :).
Click to expand...

Actually, I was going to suggest a bandsaw with a simple circle cutting jig. With a bandsaw you can produce a radius and width/depth as great or small (within reason) as you wish. Holesaws and fly-cutters can also make wonderful curved sanding blocks (though of limited width/depth) for smaller radii. You can then cut the resulting circle down to whatever size you wish for your sanding block as the radius will always be the same no matter what portion of the circle or arc you choose to use for the block.

If you wish to preserve the sanding blocks for future use, you may wish to consider making them from good plywood or MDF -- or even plastic -- for stability. Natural wood will tend to distort the curve over time with changes in humidity.
 
CrealBilly

CrealBilly

New User
Jeff
What if... I mounted the finger board to a jig.

The jig would be pretty simple on each end you would have a block with a length of slot cut at whatever radius you like. The finger board would be mounted to a length of flat stock, the flat stock would have square pins on each end that fit into the radius slot on the jig end blocks fastened to the outside of the end block by a nut so the don't move when making a cut. Then fashion a U stand for the router to be raised above the jig. Take a 1/2 staight bit and set the router to where is just touches the edge of the fingerboard then run the router down the finger board to cut the low spot of the curvature. Loosen the nuts on the end blocks and move the finger board over say a 1/4" and make the next cut, continue till completed.

As for making the sanding block the same jig could be used. perhaps with a higher U bracket for the router and reversing the jig end block to cut opposite curvature.

Shoot it might even work for a compound radius fingerboard ie 12" on one end and 16" on the other end - who knows???

Just as a side thought - not seeing any reason why the jig with the finger board attached could not be ran through a planer or drum sander also. But the sanding block would still need to be cut with a router

Just brain storming - any thoughts?
 
rcflyer23

rcflyer23

Kevin
Corporate Member
Jeff Mills said:
What if... I mounted the finger board to a jig.

The jig would be pretty simple on each end you would have a block with a length of slot cut at whatever radius you like. The finger board would be mounted to a length of flat stock, the flat stock would have square pins on each end that fit into the radius slot on the jig end blocks fastened to the outside of the end block by a nut so the don't move when making a cut. Then fashion a U stand for the router to be raised above the jig. Take a 1/2 staight bit and set the router to where is just touches the edge of the fingerboard then run the router down the finger board to cut the low spot of the curvature. Loosen the nuts on the end blocks and move the finger board over say a 1/4" and make the next cut, continue till completed.

As for making the sanding block the same jig could be used. perhaps with a higher U bracket for the router and reversing the jig end block to cut opposite curvature.

Shoot it might even work for a compound radius fingerboard ie 12" on one end and 16" on the other end - who knows???

Just as a side thought - not seeing any reason why the jig with the finger board attached could not be ran through a planer or drum sander also. But the sand block would still need to be cut with a router

Just brain storming - any thoughts?
Click to expand...


I think the only thing I have seen done with the jig I posted is that you set the router bit at the center point of the fretboard and the run it. If memory serves...
 
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