cutting perfect circles

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Hi, I have plans that call for 8", 9", and 10" dia. circles made from 3/4" stock. These will also need a routed edge all around each. The plans say use a plunge-router, but I only have a cheap regular router. I tried cutting the circles using my scroll saw, then routed the edges, and it was OK, but not perfect by any means. How can I make perfect circles? Are there router bits for my regular router that will go through material? And how do I make the circle perfectly round?
Thanks! Frank
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Use a "trammel" made from 1/4" sheet goods. There is a picture of one at:
http://www.woodworkingtips.com/etips/etip030201wb.html
You may have to drill a hole in your workpiece it you don't have a plunge router, or start with the router on the edge of the workpiece, but that is no trick. Use a straight cut bit in your router.
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Do you have a bandsaw? If so, you can make a circle cutting fixture and then do the routing after it is cut. You just push the wood on the fixture to the outer edge and rotate it on a pin to complete the cut. Rockler has a kit to make the fixture. Ed
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Do a search for circle cutting jigs for the table saw, believe it or not. For circles the size you want, "perfectly" round ones can be cut on the tablesaw. If you need a routed edge afterwards use a piloted bit.
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Larry Wasserman Baltimore, Maryland
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do you mean the bandsaw? I've never seen a circle cutting jig for the tablesaw, and frankly that sounds kind of nutty.
Mike
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yes, Mike, there ARE jigs for using a TS for circles. Freaky? :)
dave
Mike in Mystic wrote:

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it seems that way to me, but I'd like to see one - any links?
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It is a circular saw, so therefore it cuts circles, something i would never have mentioned on this list

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Yeah, I thought it sounded kind of nutty too, til I actually tried it. I've seen 2 versions, one that is fixed on the saw table & the blade is gradually raised to increase depth of cut, the other that has a slot runner and is gradually advanced into the blade to achieve the same effect. I already had a few small sleds with single runners so I just used one of those.
Before cutting the circle you need to cut a square blank, then cut the corners off to make an octagon. On a really big circle you could cut the corners again, I suppose, to make a 16 sided polygon before starting to cut the circle. The blank pivots on a pin or screw through the center. With the sliding type of jig, you move the blank so the blade just touches it, maybe cutting into it about 1/8 - 1/4 inch at the bottom, rotate the blank to cut all the way around, then push it forward a tiny bit more, repeating the process til the circle is cut all the way through. With the fixed type of jig, which is clamped to the saw table, you start with the blade low and raise it very slightly after each full rotation, similar to cutting a cove.
This safely makes about as perfect a circle as you can make out of wood, with a very clean edge. :wq
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On Fri, 05 Dec 2003 16:13:34 GMT, "Mike in Mystic"

Why? The actual cut happens at the front of the blade.
All you have to do is have the work rotate around a fixed bolt or shaft, as it passes the blade, it'll get cut. One full rotation will provide a circle.
Barry
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And the offcut neatly jambs into the side of the blade.
in message

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wrote:

In my haste to post I left out a few steps. <G>
First the 4 corners are cut off, then the 8 corners that are remaining. The idea is to get to the point where the offcuts are small and flexible.
The early cuts are made with the work FIXED, and only rotated when away from the blade. Once the rough circle is formed, the work can be smoothly rotated against the blade.
This technique is illustrated in several books, one of which is Roger Cliffe's "Table Saw Techniques". I've used it twice with great success.
A faster way to do it is to rough cut the circle with a coping saw or jig saw, and then do the final, perfect circle cut on the table saw.
Barry
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B a r r y B u r k e J r . wrote:

Hells Bells just stick it on the motor side of a lathe and mark your circle with the lathe on and start your cutting with a chisel. Before you know it you have a perfect circle and it's cut.
Rich
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On Sun, 07 Dec 2003 06:32:38 GMT, EvoDawg

This isn't so easy without a lathe. <G>
Barry
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"B a r r y B u r k e J r ."

You just need some imagination. No lathe? No problem!
Mount the wood on the shaft of a grinder motor. At 3450 RPM you get a very smoooooth finish. Ed snipped-for-privacy@snet.net http://pages.cthome.net/edhome
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wrote:

With your thought process, I could make 6' round table tops using my buddy's Piper PA-28 to turn the stock! All I have to do is talk him into taking off the prop. It's not like he can fly with all this snow. 180 HP would be plenty to keep the work moving at a steady rate.
Barry
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B a r r y B u r k e J r . wrote:

There ya go now that's using your noggin!!!!!
Rich
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I was thumbing through a book on jigs (sorry, I can't recall the full title) and there on page 34 is a picture of a jig for making circles on a TS! a pin on a sled to spin the workpiece...
dave
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I made a circle cutting jig for my router. Simply attach a piece of long thin stock to the base and drive a small nail at the desired radius (through your jig and into the workpiece). It took me a couple tries on scrap to get it calibrated but once I had one measured radius I was good to go. I started roughing the circles with a straight bit, then switched to a roundover or ogee to finish it. The only down side is the small hole in the center of your circles. BTW they sell some real cool tape at ULINE.COM It is marked off in inches so when you make something like this you can put tape on it to reindex to another size.
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Cool! Thanks everyone for the ideas! I just put together my small shop, and I'm haing a blast. One thing I've learned rather quickly was that I'll need a good dust collector very soon ;-)
Thanks!

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