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Copying A Radius


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In the past I have made my own radius sanding blocks by copying the convex radius of something else.

For example take a 5 gallon paint bucket and glue a strip of 80 grit sand paper to the outer surface.

Then take a block of soft wood like Basswood or Pine and start sanding in a perfect straight line.

After a few minutes, you have a radius sander of your own that you glue sand paper to.

It's a poor man's solution, but works well.

Now I'm challanged to find a way to copy a 14" radius.

I need to find something I can copy it from, but am drawing a blank.

Can anyone think of something easily accessable with about a 14" radius, which I could copy?

I was thinking maybe a spare tire.

Thanks for you input....

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ok but if you're not an engineer or math wiz are those formulas able to be but in simple terms? Or can someone come out with for such and such radius the wood needs to be this width and height...

Sorry never was great at math :-(

Not sure if the jig at the above link works or not, but here are some numbers, should you want to give it a shot:

R(in)   R(mm)   s(mm)   W(mm)   h(mm)   h(in)

10	  254	 9	   150	 10.921  0.430

12	  304.8   9	   150	 9.095   0.358

14	  355.6   9	   150	 7.797   0.307

16	  406.4   9	   150	 6.827   0.269

20	  508	 9	   150	 5.469   0.215

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A nail, some string, and a pencil...

Punch in the nail, tie some string to it.

Tie the pencil to the other end of the string.

Wind up the string around the pencil, until the distance between the pencil and the nail is as desired.

Draw your radius, making sure the string is tight the whole time....

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I know this is kinda a afro engineering way of doing it but it should work.

First you can make this router circle jig

Then just set it up to cut a 14 in radius in some mdf or plywood then once you've got your 14 in radius hole just cut it into sections and glue them one on top of the other for as thick as you need then you should be good to go.

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You guys have seen this, right?

http://www.projectguitar.com/tut/radius.htm

About the first thing I ever posted on here!

Sure have

I actually used it once....but Im always looking for other ways to do things :D

Actually Radius jigs are one of the most clever things I see on this site...eveyone has their own little way.

I wanted to take pictures of the one I made the other night, but the wife didn't let me get into the workshop lastnight; I will try again tonight.

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Looks like a clever device.

I don't understand how you use it though...

Doesn't in generate a concave cut?

So, how would that work for the fingerboard you have pictured?

the wooden block beside the board is what you make with the router then you make the board with the block.

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OK, So here is the scoop.

I tried to make a modified version of the tool that was liked here in this thread.

I would have worked in theory, but my idea of using plastic instead of MDF failed. I prooved to be way too flexible.

Oh well.

I trying something else tonight, if it works out (and I think this one will), I will post some pics and an explaination.

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