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?
Use a "trammel" made from 1/4" sheet goods. There is a picture of one at:
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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.
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
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.
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.
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 ;-)
Using a router is probably your easiest bet, using the trammel idea from the first post. If you make it long enough you can make multiple pivoting points at 8", 9", and 10" and beyond. Now a word of caution, depending on the hardness of the stock you might want to make successive cuts, say at 1/4" then 1/2" and finally all the way through. Trying to cut through 3/4" stock with a less powerful router, and/or a bit that might not be as sharp as when new can be a bear, or dangerous, or both. Take your time and be safe.
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
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.
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.
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.
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