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Subject:
Re: How to best cut a large circle

John in NM
The first time I did this was one of my first assignments in the furniture shop I worked for - I'd just been promoted from bulk parts cutting to assembly & joinery work. One of the other guys briefly explained "use a router".

No one mentioned that they had a plunge router around (only one, beat to death from over work). So I had the fairly heavy top on a rolling cart but didn't clamp it down because it seemed so heavy it wouldn't move. Roughed out the circle with a jig saw and figured I could use a regular router because the circle guide was made out of fairly flexible thin plywood - figured I could just kinda bend it in to start the cut since the cut was one sided and only ~1/8" of material.

Got a nice sharp bit, a spiral flute one because they give you a nice clean cut on endgrain - roughly 1/3 of the circumference of the top.

Students of physics can probably predict how this all worked out, it was 10 seconds of slapstick worthy of Buster Keaton that left me standing there with a shocked expression, holding a router screwed to a broken plywood jig, that mobile table rolling one way and an almost round top rolling the other way.

Needless to say, I now use a plunge router for this stuff, though I still do rough out the circle with a jig saw, not liking to take the full cut with a router bit and load down the router excessively (most of my bits are 1/2").

I've seen it done with a jig on the table saw too, but I don't know the nuances of doing it that way. I think I would rough it out on the BS or with a jig saw, figure out a method that will hold the center pivot down using the miter slot and still support the table corner right at the blade to prevent chipping, and use the saw to clean up the cut. Since you'll be trimming off just a little on a tangent to the curve (set your pivot point in front of the blade, obviously, so that the finished curve tracks away from the spinning blade).

I think I would also figure a way to use a feather board or other drag fixture to help keep this from running away on you like my router did the first time.

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