# Large Radius Arcs



## ducbsa (Jul 6, 2014)

I made a rough cut with my saber saw first, then made 1/8" deep passes with the router bit and cut the pieces long for dealing with chipout. The screws holding the piece to the long board are into the backside. Something similar could be used on a bandsaw, too.


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## ducbsa (Jul 6, 2014)

Ooops, no good on a band saw!!


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## bzguy (Jul 11, 2011)

I made a fairly sophisticated jig for cutting circular table tops on a band saw.
It had a sliding piece of flat stock recessed into a slot with a "Prick-point" to mount the center of the blank square top on so it could revolve and be cut.
In the bottom of the lot I contact cemented a measuring tape blank so that the radius could be determined with no trial and error.
This necessarily had to be on an extension opposite the small throat of the saw, otherwise only relatively tiny tables could be cut.
Crucial to this arrangement was a hinge that allowed you to slide the square top into the blade to get the cut started at the correct radius.
I also mounted a router on the same jig that could be "bumped" in a 16th" or so to clean up saw-marks for a perfect edge.
A picture of it was in an industry magazine about 25 years ago, long gone.


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## woodnthings (Jan 24, 2009)

*large radius circles*

Ya know, a circular saw will cut a large radius, IF you don't lower the blade more than 1/8" to 1/4" per pass. You would just need to make a base plate arm and a pivot to hold the radius constant on your plywood or sheet goods.






I once made a 10 ft long arm for a router to make a constant curve for a head board, but I didn't like the radius even at that length. I ended up just making it straight across:
http://www.woodworkingtalk.com/f2/mission-headboard-build-37911/

The issue with cutting large circles on the bandsaw is the starting cut. I drill a 3/4" hole on the line I wish to cut, then cut a slot for the blade leading to the hole. Of course you need a pivot and a support arm to maintain a constant radius. For a lot of work like this, a bracket mounted to the right side of the table to hold the arm and pivot would be a time saver.


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## m.n.j.chell (May 12, 2016)

The circular saw idea won't work for inside curves, as shown. 
The jig you've shown for it, though, could be modified to work with a router.


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## woodnthings (Jan 24, 2009)

*I donno?*



mikechell said:


> The circular saw idea won't work for inside curves, as shown.
> The jig you've shown for it, though, could be modified to work with a router.


What's the difference.. inside or outside, if it cuts the circle, the saw don't care? :| I don't know what you might do with large inside circles, but what ever.


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## m.n.j.chell (May 12, 2016)

The wood he shows in the original post is much thicker than the particle board in that video. And it shows an inside radius being cut.

The radius of the saw blade will cut the wood. You can't get a clean inside radius on thicker material with a circular saw blade.


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## woodnthings (Jan 24, 2009)

*The saw is almost "fully retracted"*

The radius of the blade only comes into play when the blade is fully extended as it might be on very thick material. What happens is that the kerf gets widened out by each succeeding pass at the lower depth. You just have to allow for that and not force the saw as you make your passes..... It will do in a pinch and is not the preferred method for the cleanest cut.


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## m.n.j.chell (May 12, 2016)

No matter how shallow or deep the cut ... the circular blade will cut a "bowl" shape into an inside radius. In fact, if I am not mistaken, the shallower the cut, the more pronounced the "top to bottom" curve of the cut will be.


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