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Determining a radius cut

This is a discussion on Determining a radius cut within the Jigs and Fixtures forums, part of the Routers category; I came across a note on in a article that mentions a radius cut of ...


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Old 06-22-2008, 10:36 AM   #1 (permalink)
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I came across a note on in a article that mentions a radius cut of 40". The length of the wood piece is only about 24". I know how to cut arcs and circles from the jigs I have made for my other tools but I have not seen a radius described that way before.

Does this mean center my arc jig on the length of the board (12") and nail it down at 20" (half of 40") to achieve the correct arc for the radius.

Any help would be appreciated.

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Old 06-22-2008, 02:52 PM   #2 (permalink)
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I was thinking I could have described this a little better. Does a 40" radius mean essentially a 40" circle?

I am going to try a back into the answer with a little trial and error since I know all the dimensions and how to calculate the radius.
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Old 06-22-2008, 05:15 PM   #3 (permalink)
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Roy,

If your radius is 40" (inches) then the diameter of your circle will be 80". The circumference of the circle will be 3.14 times the diameter. That's a big circle! If your board is only 24" in length, then I would think your first calculation to be right.

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Old 06-22-2008, 05:54 PM   #4 (permalink)
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Quote:
Originally Posted by cbsjoez1935
Roy,

If your radius is 40" (inches) then the diameter of your circle will be 80". The circumference of the circle will be 3.14 times the diameter. That's a big circle! If your board is only 24" in length, then I would think your first calculation to be right.

Joe Z.
Thanks Joe. The more I thought about it the more it seemed correct. I guess I have just not heard the arc described that way before.

Got tied up today but this evening I am going to just lay it out on a piece of paper and draw the radius. In this case I know what the final dimensions should be. I need to get this one right because I have a nice piece of cedar I am going to be working on.

Thanks for the help.
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Old 06-22-2008, 06:17 PM   #5 (permalink)
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HI Roy

Definitions of radius

* the length of a line segment between the center and circumference of a circle or sphere
* a straight line from the center to the perimeter of a circle (or from the center to the surface of a sphere)
* a circular region whose area is indicated by the length of its radius; "they located it within a radius of 2 miles"
* the outer and slightly shorter of the two bones of the human forearm
* spoke: support consisting of a radial member of a wheel joining the hub to the rim
wordnet.princeton.edu/perl/webw

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Last edited by bobj3; 06-22-2008 at 06:19 PM.
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Old 06-22-2008, 08:09 PM   #6 (permalink)
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Nice Bob

You forgot one:

R = ((L^2) + 4(H^2)) / 8H

Radius I understand, just not in the context that I ran across it. I am good now though.
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Old 06-22-2008, 11:18 PM   #7 (permalink)
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I don't know what the article is about but assume that a 24" length of wood is going to be curved, in which case mark the centre of the wood, draw a line 40" long at right angles to the centre of the wood and with a jig or a piece of string with a pencil tied to it's end draw an arc on the wood. These shots show in a crude but fast demo.of how I interpreted your first post.
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Determining a radius cut-radius1.jpg   Determining a radius cut-radius2.jpg  
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Old 06-23-2008, 08:10 AM   #8 (permalink)
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Harry you are correct. Here is a picture that I refer to all the time to keep my mind straight.
[IMG][/IMG]
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