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post #1 of 34 (permalink) Old 08-17-2010, 03:20 PM Thread Starter
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I know I need a 6 1/2" corner radius. How do I use my compass to determine the 6 1/2"?
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post #2 of 34 (permalink) Old 08-17-2010, 03:41 PM
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Hi

From each side ,but a mark at 3 1/4" out from the corner , take your sq. and draw a line to the center of the board on both marks, where the lines cross put your compass point on the X mark and draw your radius, from each edge of the board..

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I know I need a 6 1/2" corner radius. How do I use my compass to determine the 6 1/2"?



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post #3 of 34 (permalink) Old 08-17-2010, 04:23 PM
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Bob, I think it should be 6-1/2", not 3-1/4", unless I don't quite understand correctly.

In other words, put marks 6-1/2" out from the corner on both edges. Take your square and draw lines from the marks perpendicular to the respective edge into the board. Where the lines intersect, put your compass, set it to 6-1/2" and draw the radius.

In yet other words: draw a 6-1/2" square at the corner in question. The corner of the square that's farthest away from the corner of the board is the one you put your compass at.

MM
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post #4 of 34 (permalink) Old 08-17-2010, 05:27 PM
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Bob, I think it should be 6-1/2", not 3-1/4", unless I don't quite understand correctly.

In other words, put marks 6-1/2" out from the corner on both edges. Take your square and draw lines from the marks perpendicular to the respective edge into the board. Where the lines intersect, put your compass, set it to 6-1/2" and draw the radius.

In yet other words: draw a 6-1/2" square at the corner in question. The corner of the square that's farthest away from the corner of the board is the one you put your compass at.

MM
Don't know anything about it...but I'll chime in anyway. Using Bob's method, you get a circle with a 3-1/4" radius and a 6-1/2" diameter, which I totally don't understand. To me, I think your answer is correct as far as radius.

You can also use a little math and trig to figure out where to set your compass, but the above would be easier, me thinks.
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post #5 of 34 (permalink) Old 08-17-2010, 07:32 PM
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If the edges are already cut, then drawing the square would be the best solution. If the edges are not cut but the outline of the shape is drawn, then all that's needed is the compass set at 6-1/2". This si really very fast and easier than drawing 2 more lines to make a small square.
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post #6 of 34 (permalink) Old 08-17-2010, 08:32 PM
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If the edges are already cut, then drawing the square would be the best solution. If the edges are not cut but the outline of the shape is drawn, then all that's needed is the compass set at 6-1/2". This si really very fast and easier than drawing 2 more lines to make a small square.
Yes, indeed. The drawback, and the reason I have not suggested this method is that small errors in initially setting the compass add up to potentially become a significant error. I think, first measuring the distances with a ruler and a square might give a smaller error, but I haven't calculated the error propagation as I don't know the errors in the rulers, squares and compass involved.

There are quite a few methods. Either one of the mentioned two will work.

MM
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post #7 of 34 (permalink) Old 08-18-2010, 12:18 PM
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Yes, indeed. The drawback, and the reason I have not suggested this method is that small errors in initially setting the compass add up to potentially become a significant error. I think, first measuring the distances with a ruler and a square might give a smaller error, but I haven't calculated the error propagation as I don't know the errors in the rulers, squares and compass involved.

There are quite a few methods. Either one of the mentioned two will work.

MM
Using a compass will introduce some error in that the initial setting of the compass might be off but if this is not changed, the result will be that the final radius is off by the same amount. This is usually okay. The only other errors would be placement of the compass point at the exact intersection of the arc. The width of the pencil lines can be controlled to minimize some of this error but the wood grain may cause the point to shift slightly when placing the compass; however, all this is tiny compared to actually making the cut.

Another method would be to make a pattern of the radius and use a router to cut them.
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post #8 of 34 (permalink) Old 08-18-2010, 12:53 PM
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Welcome to the RouterForums Bluebonnetcabins. Thanks for becoming a member of our community.




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post #9 of 34 (permalink) Old 08-18-2010, 01:11 PM
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Hi Guys

I'm not a big fan of using the router and a templates on the corners, you will always have a upgrain on the corners that the router bit will lift up and rip out , I think by using a good jig/band/scroll saw it will cut the stock without ripping the stock out, but by using a template to mark the stock they will all be the same radius..

Most jig saws come with a edge guide that can be drill out with a 1/8" hole for a pivot pin and can be use just like a cir.jig you can buy blades for the jig saws that will cut as smooth as a router bit, once set the radius will be all the same. (Bosch blades)


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Originally Posted by RJM60 View Post
Using a compass will introduce some error in that the initial setting of the compass might be off but if this is not changed, the result will be that the final radius is off by the same amount. This is usually okay. The only other errors would be placement of the compass point at the exact intersection of the arc. The width of the pencil lines can be controlled to minimize some of this error but the wood grain may cause the point to shift slightly when placing the compass; however, all this is tiny compared to actually making the cut.

Another method would be to make a pattern of the radius and use a router to cut them.



"It's fine to disagree with other members as long as you respect their opinions"

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Last edited by bobj3; 08-18-2010 at 02:49 PM.
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post #10 of 34 (permalink) Old 08-18-2010, 02:35 PM
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Just to verify cutting corners with the bandsaw or jig saw is not the best way to cut corners...the router does the best job and you can make all corners exactly the same and you don't need to cut up-grain ever see my how to video here

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On January 17th, 2020 Dad passed Away at the age of 87 and I will miss him very much. If anyone is interested there is a memories website https://memories.routerworkshop.com/
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