I needed a circle-cutting jig for this project, and I decided to make one that was 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 worked great and was relatively simple to build out of scrap plywood lying around the shop. This is a similar jig to the Oval router jig I made.
Click here to download the project plans
So I needed to cut a massive circle for a table project I’m working on, and honestly, trying to freehand something like that is just asking for disaster. Instead, I decided to make myself a proper circle cutting jig for my router. And let me tell you, this thing turned out pretty sweet.
The best part? It’s got an incremental swing arm for precision, it attaches to your material without wrecking it, and you can adjust it to dial in the exact radius you need. Let me walk you through how I made it.
Starting with the Swing Arm
First thing I did was rip a strip off some scrap plywood to make the swing arm. You can make yours as long as you want, depending on how big your circles need to be—mine ended up being about 2 feet long. (If you want all the exact measurements, I’ve got a sketch up on my website.)
I marked down the center line and then laid out 1″ increments along the entire length. Then I took it over to the drill press and drilled ¼” holes at each of those marks.
Making the Pivot Point
Next up, I grabbed some ¼” plywood and cut a perfect square, marking the center point. I used a Forstner bit to countersink a spot for a T-nut, then switched out the bit to drill the through-hole.
Here’s a little trick: I positioned the T-nut over a dog hole on my bench and just drove it home. Now, I’m sure I could’ve tracked down a shorter T-nut that wouldn’t poke through the other side, but that’s what I had on hand, and I really didn’t want to drive across town for a 50-cent piece. So I just filed the pointy bits flush with the bottom.
To make room for the shaft of the T-nut, I ran a dado down the center of the swing arm. Oh, and pro tip: make sure your pivot point plywood is about the same thickness as your router’s base plate. Trust me, it’ll make assembly way easier.
Building the Router Bracket
Time to make a bracket that would attach the jig to my router. I ripped off another piece of scrap plywood and measured the distance between the mounting holes on my router base.
After drilling some through-holes, I did a quick test fit and marked where I wanted to cut it so I wouldn’t have a bunch of extra material hanging off. Chopped it at the miter saw.
Then I countersunk for the bolt heads—which honestly would’ve been easier to do before I drilled the through-holes, but hey, I was just making this up as I went along.
Assembling Everything
I grabbed another piece of scrap plywood and figured out the width by just holding it up against what I’d already made (without the base plate attached). Marked the length, cut it at the chop saw, and then pre-drilled some screw holes.
I flipped it over and pre-drilled holes on the other side too—one set to attach to the swing arm, another set for the mounting block I’d made earlier.
Then it was just a matter of gluing and screwing everything together. First I attached it to the swing arm, then I attached the mounting block to the router.
The bolts stick out about 1½”, which gives you a little over an inch of adjustability between the different pivot holes you drilled in the swing arm. Pretty handy for fine-tuning!
Using the Jig
When it’s time to actually cut your circle, here’s what I do: I line up the T-nut points with my layout lines on the workpiece, mark the perimeter so I know exactly where to put my double-stick tape, and stick the pivot point down.
Then I pick a pivot hole that’s close to the size circle I want. While I’m at it, I marked out the radius measurements in inches right on the swing arm—makes it super easy to get in the ballpark.
Finally, I use the mounting bolts to fine-tune the radius to match my layout line perfectly, and then I’m ready to cut.
And that’s it! The jig worked like a charm, and my circle came out perfect. Now I can actually finish this table project.
Stay tuned—my next post is going to be all about building that round table.
I’m the owner of Benham Design Concepts, a mixed media art studio where I design and build custom furniture and other works of art using wood, glass, stone, and various metals.
In this blog, I talk about the art I create, my journey, and the things I learn along the way.