How I make perfect circles

[Phil Thien]

My cyclone separator top research requires lots of circles. I wanted a way to make 'em fast and make 'em perfect.

I created a jig that allows me rough them out with a jigsaw or bandsaw and then use the jig and my router table (with a flush cutting bit) to true them.

I use the same jig to cut holes.

I've included some pics here. More info at http://www.cgallery.com/jpthien/cj.htm.

[Eric Mims]

that's interesting, thanks for the pics and the idea.

[Lee Schierer]

I'm curious about photo #3. Did you cut the inside of the ring with your jig?

[Phil Thien]

I'm curious about photo #3. Did you cut the inside of the ring with your jig?

Yes, the inside was cut using the following procedure:

(1) Drill a 1/4" pilot hole as the center of your hole. (2) Adjust the jig's pivot to the correct radius for the desired hole. (3) Use the jig as a compass and (using a pencil) draw an outline of your hole on the wood. (4) Drill a 1/2" starter hole just inside of the pencilled outline. (5) Finally, using your router table with a 1/4" flush-trim bit (inserted through the starter hole), along with the jig, cut your hole. NOTE: As you finish the hole, the center pivot point will be unsupported which can lead to a ragged finish to your hole. I suggest inserting pieces of 1/4" dowel in the bit's cutting path as you progress to keep the middle (waste) centered in the hole.

When I'm cutting circles (and only have to flush-up the rough cut), I use a 1/2" two-flute flush-cut bit (I use the Whiteside 2405 available from Holbren on this page: http://www.holbren.com/home.php?cat=60).

When cutting holes (I made the ring by first cutting a circle and then cutting a hole in the circle), I use a 1/4" flush-cut spiral bit (I use the Whiteside RFT2100 available from Holbren on this page: http://www.holbren.com/home.php?cat=90).

When cutting holes you're cutting the full thickness of your wood in a single pass so you want to avoid pushing the stock too hard. I cut mostly MDF with this jig and it cuts like butter. When I've needed a large hole in other material I'll often use the jig to make a template in thinner material (I then use the template to flush-up the hole in my wood after cutting it with a jigsaw).

[Eddie Darby]

Sweet post! I will have to try that!! Thanks.

[Cary Swoveland]

What a clever idea! So simple--once you've seen it, that is.

Here's a thought for a small mod, for cutting inside circles. Rather than pushing the V at the end of the jig against the bit's bearing, what about pulling the bearing against a V at the end of the jig's diameter-adjustment slot? That way, any loss of contact between the jig and the bearing won't spoil the piece.

Cary

[Phil Thien]

What a clever idea! So simple--once you've seen it, that is.

Here's a thought for a small mod, for cutting inside circles. Rather than pushing the V at the end of the jig against the bit's bearing, what about pulling the bearing against a V at the end of the jig's diameter-adjustment slot? That way, any loss of contact between the jig and the bearing won't spoil the piece.

Cary

That is the way it works. For inside circles I use a 1/4" upcut spiral, so it may be hard to see in the photo that there is a 1/4" bearing contact point there.

[Cary Swoveland]

That is the way it works. For inside circles I use a 1/4" upcut spiral, so it may be hard to see in the photo that there is a 1/4" bearing contact point there.

Thanks for the clarification. I'm not sure how I missed that the first time around.

Cary