Router Jig For A Perfect Circle


We once enlisted a contractor to cut a plywood circle for a cat condo we were building. Now we’re embarrassed that we couldn’t come up with a solution as eloquent and easy to use as this circle cutting router jig which [Grays42] built.

He’s using a small trim router for the job. The jig is made up of two thick-walled pieces of PVC pipe. We don’t think the router is attached to jig. Instead you hold it against the wooden spacer which is on the outside edge of the cut. He doesn’t mention how he made the spacers, but we’d recommend cutting a hole the size of the pipes and then ripping down the middle to remove some of the material (tape the two spacers together during fabrication to ensure proper alignment). It just takes some nuts and bolts from the hardware store to assemble everything.

[Grays42] is using this to cut rings for his telescope build. We have our eye on it for making our own wooden Bulbdial clock.

[via Reddit]

36 thoughts on “Router Jig For A Perfect Circle

    1. Precision and tolerance for a wood lathe ?
      Have you operated one recently ? You hold the tool by hand and work everything byt the feeling, there is not even a ruler scale even less DRO possible…

      SERIOUSLY, try a wood lathe once… or try woodworking first…

  1. New Yankee Workshop is full of simple jigs like this. There was something similar to this that let you cut out very large (but perfect) circles using a bandsaw. Instead of the saw moving, you rotate the piece through the saw on a pivot.

    1. Been usin’ that bandsaw jig for years for blanking radius casings. Largest ever was 14′ radius. Have used similar to radius decks with a 4-1/4 x 1/2 flush trim bit in the router

  2. If you look at the central piece of wood there are 2 side screws with their tiops coming almost through on the other side, so I think it’s clear that it’s attached to that spacer to keep it steady rather than being merely pushed against it manually.

      1. Yeah, I did, and it’s always worked fine for me.

        perhaps it’s just a problem with the way that you are using the tool.

        that said I also would normally cut a circle by marking with a pencil and free-handing with a scroll saw, practice makes perfect. if you can’t do it you just didn’t practice enough yet!

        1. I still don’t think a string is that helpful.

          And as for me, I know I have very little experience with routers, but I also had moments that I thought I got it and then it slipped away..

          Also I’d draw then use a jigsaw for an occasional circle, but that might be related to my lack of router skills.

      2. A router may not be like using a pencil but my script is more legible if I use a router than a pencil. I’ve made hundreds, maybe thousands of decorative hand routed signs for craft shows. I’d actually intentionally mess my text up to give them some more charm. The trick to doing hand carved freehand lettering is in using the right kind of router. I like using plunge routers to do it myself. People have accused me of using templates in order to do some of my signs, but I can assure you I’ve done them all freehand. I suppose the bit used is fairly important too. I’ve used straight, and rounded, but I mostly prefer using a V carving bit to letter with.

        1. Well, you my friend are an anomaly…

          I’ve been using routers for more than 30 – 35 years; plunge routers are my favorite for heavy duty stuff (and I have some nice jigs for that) but I have a new palm sized router I picked up that I absolutely love. I think I’ll build a CNC around it.

          That said… I can’t route a straight line without a template. I can come somewhat close but there will always be a tell-tale spot that got away from me somewhere along the line and there is no way a piece of string is going to help me in that regard. I have a couple of ABS plastic jigs I made up for circle cutting.

          Anyway, I envy your skill!

          1. Yeah you just have to man up and hold the router steady. Lock your arms! Sometimes a router gets away from me too, I call those signs firewood. Actually I can usually clean them up with some chiseling, or passing the router deeper through the cut again. These are freehand lettered signs so some artistic license is to be expected.

            I know I’m an anomaly. I’m like Batman and Superman rolled into one! All I’m missing is the superhero costume …

            I have 2 plunge routers, an odd Chinese one, and a Hitachi M12V. I treated myself after I’d made thousands of dollars with the cheap Chinese router. I have the old Hitachi model, the really ugly blocky one. I’ve been routing a few years myself.

  3. I did this same thing with a piece of hardboard and it was very simple. I just drilled the hardboard so it could replace the base of my router, located a screw for the center pivot, and called it done. All that was needed was to place the center pivot screw, plunge the cut, and rotate.

  4. Lets add linear actuators, quadrature encoders, and a Microcontroller and make it do ellipses. That’ll definitely “hack it up”.

    Nice build though. Some alternatives could be all-thread and nuts instead of pipe. Or, even smaller shafts (like the slides of an old printer) with set screws instead of the wood clamping the pipe. There are a wide variety of ways this could be done depending on what you have available. I would just go through the scrap bin and see what you have that would work.

    Personally, I use a thin 1/4″ plywood with a hole for a pivot point. You can just mark which hole you used and it is a easy reference to repeat that size circle.

  5. “(tape the two spacers together during fabrication to ensure proper alignment)” The fact that you think the pipes must be well aligned and parallel tells me all I need to know as to why you couldn’t come up with a jig on your own…

  6. Routing is all about making the correct jig for the work you want to achieve. The possibilities are maybe not endless but huge.
    A upside down router table is a must build. I also made some tools for chamfer or rectification. My rooter is my favorite tool and it is usually underrated by many people who did not think enough about the versatility of the tool.

      1. Well, safety first, you have to be concerned by safety at all time and even more when upside down. A good table will include a easy on off device (=avoiding elastic for example), a knock out shut down and of course all necessary protection around the tool. Usually you can build good safety devices fast with… your router.

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