I needed a circle cutting jig for this project, and decided I wanted to make one that is adjustable to whatever size I needed. I also wanted one where I didn’t have to drive a nail or screw into my work as the pivot point. It works great and was relatively simple to build out of scrap plywood laying around the shop
Click here to download the project plans
Video Recap
Today I’m making this circle cutting jig because I need to cut a huge circle for this table.
It has an incremental swing arm, a non-destructive way to attach it to your material, and is fully adjustable to dial in the exact radius you want.
So to get started, I ripped a strip off some scrap plywood to act as the swingarm. You can make this strip as long as you want to make as big of a circle you. For this jig, I am about 2 feet long.
I do have a sketch on my website if you want all the measurements.
I marked down the center and laid out 1″ increments.
I head to the drill press to drill ¼” holes down the length.
Then I used some ¼” plywood and cut a perfect square and marked the center.
I used a forester bit to countersink for a T nut and switched out the drill bit to drill the through-hole.
I positioned the T nut over a dog hole and drove it home.
I’m sure I could get a shorter T nut that wouldn’t stick through, but this is what I had on hand, and I didn’t want to drive across town for a 50cent piece, so I just filled the points flush.
To make room for the shaft of the T nut, I just ran a dado down the center of the swingarm.
I should mention that your pivot point plywood should be about the same thickness as your base plate. It will make assembly a little easier.
I ripped off a piece of scrap plywood to start making a bracket to attach the jig to the router.
I measured the distance between the holes on my router.
Drilled some through holes
Did a test fit and marked the length so I wouldn’t have a bunch of extra material sticking out, and cut it off at the chop saw.
Then I countersank for the heads of the bolts, this would have been easier before I drilled the through-holes, but I’m just making it up as I go.
I got another scrap of plywood and marked the width I by holding it up to what I had already made. I did this without the base plate attached.
Then I marked the length and cut it off at the chop saw.
I pre-drilled some screw holes to attach it to the swingarm, and flipped it over to pre-drill some holes to attach it to the mounting block I had made earlier.
I then glued and screwed it to the swingarm.
I then glued and screwed it to the mounting block in the router.
The bolts stick out about a 1 ½” so you have a little over an inch of adjustability between the pivot points drilled in the swingarm.
To locate the jig on your workpiece, I line the points up with my layout lines, mark the perimeter, so I know where to put the double-stick tape, and stick her down.
I pick a pivot hole close the size I want, and while I am there, I marked out the radius in inches along the swingarm.
Then using the bolts, I fine-tuned the radius to my layout line and cut the circle.
Stay tuned; my next video will be of the round table build.
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