Instructables

This instructable will show how to make an accurate and easy to use jig for cutting perfect circles with a router.  There are many pre-made circle cutting jigs on the market, but they are fairly expensive, and many of them don't have a very large maximum radius.  Several of them also rely on a series of holes to control the size, which can be a problem if you need a very precisely sized circle that happens to be in between the sizes of two of the holes.

I will show how I made a precise circle cutting jig using nothing but scrap plywood, and a few nuts and bolts.  This basic plan can be modified to make accurate circles of almost any size.

Disclaimer:
Please practice shop safety, especially when working with power tools.  Take all neccesary safety precautions, and don't use any tools or procedures you're unfamiliar with or uncomfortable using.

Step 1: Tools and Materials

Tools-
router
1/4" router bit
3/4" router bit
straight edge
pencil
drill or drill press
1/4" drill bit
chamfer bit
saw (prefferably a tablesaw or bandsaw, but any will work)

Materials-
Scrap of MDF or cabinet grade plywood
1/4"x20 tpi threaded rod 3" long (or a 1/4"x20 tpi bolt with the head cut off)
1/4" x20 tpi T nut (or pre-made t-handle)
1/4"x20 tpi standard nut
3/4" OD washer

I don't have a cost for the materials, because it was made entirely from items I had on hand.  I would think that most of not all of these materials could be found in most workshops.  The cost to purchase these items would only be a few dollars.  It does of course assume that you have a router to use the jig with.
 
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Thank you
 A very well presented instructable.
Thank you for sharing it.
gdufford4 years ago
Nice looking jig. Having a good jig is the secret to most of my successful projects.

I use this circle cutting technique frequently, but I just take a long strip of fiberboard and set it up for a fixed radius. The fiberboard is nice and thin (1/8 inch) so you don't need to cut a recess. I just posted my Cardboard Ball Chair  (www.instructables.com/id/Cardboard-Ball-Chair/) and the 4' turntable of the jig was made this way.

If I cut a lot of circles of various sizes I'd certainly make a jig like this.

Another similar technique I used once was with a 6 foot long piece of 3/8 inch all-thread for the radius arm. The all-thread allowed for very precise adjustments and long radii. I used this to make concentric rounded grooves in an old wood door. The resulting pattern made the door from a very junky piece to something that looked like art.

I love using radius techniques whenever possible. You can do a lot with them.
Re-design5 years ago
Good job.  I love PC routers.
kelseymh5 years ago
Good complete writeup, thanks!  I especially like your home-made star handles :-)