I have just completed a circle cutting jig for my band saw. Scribing a circle in thin material using a compass is relatively easy but with thicker plastic it can become problematic. The neat thing about this jig is:
1 - It replaces a bunch of plywood boards I used with holes drilled at various radii. I would have to line up the blade with the dowel insert then cut blanks to almost the exact diameter of the circle I wanted to cut otherwise they would not fit between the blade and the dowel. Add to this the inaccuracy of locating the center of the blank to drill a hole and most times I would end up with flat areas on the edge of the circle I cut.
I would have to cut circles about 1/8-1/4 inch oversized and then sand smooth after gluing to a tube.
2 - Since this jig travels on a runner in the band saw's miter track I can now set the radius as precise as I want and make the blank oversized. I place the blank on the jig then push the jig into the blade. The jig has positive stops on the bottom so it always aligns with the blade. There is a dado cut into the jig that allows me to move the wood piece with the dowel back and forth to the correct radius. It also has about 3 inch overhang on the front of the saw so I can clamp the dowel piece in place. At the back of the jig is a separate wood piece that I push forward to act as a zero clearance insert. If I left this area open then the plastic blank will flutter ended up in an uneven cut.
An overall picture of the jig with the plastic blank
Here I have set the dowel at the correct radius. You can see the gap between the blade and the dowel board.
I slide the jig out from the blade push the zero clearance board up against the dowel board then insert the blank.
Then it is simply a matter of pushing the jig into the blade and cutting the circle
The result is a perfect circle
Though I will be using this jig for my model RR business it can be used to cut circles out of any material the blade is compatible with. The overall size of the jig will allow circles up to almost 2 foot diameter.
Also the jig can be sized to accommodate anyone's smaller bench top band saw provided there is a miter track on the band saw base.
