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.

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

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

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.
<p>Once you tighten the nut to hold the desired size of the circle, it seems like you will be tightening the fixture to the work piece making it hard to go around.?</p>
Thank you
&nbsp;A very well presented instructable.<br /> Thank you for sharing it.
Nice looking jig. Having a good jig is the secret to most of my successful projects.<br /> <br /> 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&nbsp; <a href="http://www.instructables.com/id/Cardboard-Ball-Chair/" rel="nofollow">(www.instructables.com/id/Cardboard-Ball-Chair/</a>) and the 4' turntable of the jig was made this way.<br /> <br /> If I cut a lot of circles of various sizes I'd certainly make a jig like this.<br /> <br /> 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. <br /> <br /> I love using radius techniques whenever possible. You can do a lot with them.<br />
Good job.&nbsp; I love PC routers.<br />
Good complete writeup, thanks!&nbsp; I especially like your home-made star handles :-)<br />

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