View Full Version : How I make perfect circles
Phil Thien
12-30-2007, 11:49 PM
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.
http://www.cgallery.com/jpthien/graphics/cjtop.jpg
http://www.cgallery.com/jpthien/graphics/cjdet4.jpg
http://www.cgallery.com/jpthien/graphics/cjring1.jpg
Eric Mims
12-31-2007, 1:04 AM
that's interesting, thanks for the pics and the idea.
Lee Schierer
12-31-2007, 9:41 AM
I'm curious about photo #3. Did you cut the inside of the ring with your jig?
Phil Thien
12-31-2007, 10:42 AM
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
12-31-2007, 3:20 PM
Sweet post! I will have to try that!! Thanks.:)
Cary Swoveland
01-04-2008, 1:40 PM
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
01-04-2008, 4:25 PM
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
01-04-2008, 4:58 PM
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
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