Cut perfect circles and arcs using any plunge router that accepts a standard Porter Cable style template bushing.
If you occasionally cut circles and arcs, then a shop built circle cutting jig is likely all you need. However, if you cut a lot of circles and need them to be consistently at precise diameters, a commercial jig is the way to go. The WoodRiver circle cutting router jig is well made, easy to use and does the job beautifully.
This jig, CNC machined from a billet of solid aluminum, enables you to cut consistently accurate circles between 2-1/2″ and 32-1/2″ using the two supplied 1/2″ steel rods. But, you can effectively cut circles of any diameter by using two user-supplied 1/2″ steel or wood rods. The jig comes in a carboard box with a foam insert that keeps all the parts together for convenient storage.
You need to use a 1/4″ router bit with the jig – I suggest using a spiral up-cut bit. I find it cuts much faster than a single flue straight bit. It also pulls the chips up and out of the workpiece towards the router. You’ll find this jig much more convenient that using a jig saw or band saw, which typically leave rougher edges that need a lot of clean-up. A sharp router bit will give clean edges that require little or no clean-up.
Ideally you’ll also want to use a dust extractor with your router, especially if you’re cutting MDF, which produces a lot of fine dust. Excessive dust accumulation can interfere with the accuracy of your cut.
Setting the diameter of the circle you want to cut is very easy. The first thing to do is install a 1/4″ bit and the guide bushing in your router.
Then attach your work piece to a sacrificial base. I do this using a couple of small strips of double-sided tape. You should also clamp the assembly to your workbench.
Next you’ll draw registration lines on the work piece, intersecting at the center point of your circle.
There is a sealed bearing on the base plate and centered markings that you use to align the base plate when cutting the pivot hole. You’ll also see markings that establish the inside and outside edge of the router bit. You use the outside edge marking when you want to rout a hole in your stock and the inside edge marking when you want to rout a circle.
Position the base plate over the center lines you penciled on your work piece and then rout a hole for the pivot pin. (Note, Woodcraft also includes a 1/8″ pivot pin that you can use if you want a smaller hole in your workpiece. If you use it, remember to rout the hole for the pivot pin with a 1/8″ router bit).
Insert the pivot pin into the 1/4″ hole on the tailstock and then into the hole on your workpiece.
Finally, you set the cut distance for your circle, using the radius of the circle. In the photo below I’ve set a distance of 8cm to cut a 16cm circle.
You can now rout the circle. It’s a good idea not to cut too deep – I rout about 1/4″ of material on each pass. Remember to move the router counterclockwise.
After using this jig a couple of times I found that I could set it up and rout a circle in well under 10 minutes. The WoodRiver circle cutting jig is well made and does exactly what it’s designed to do perfectly. Anyone who cuts a lot of circles will appreciate it’s robust build, ease of use and it’s ability to produce consistently accurately sized circles.
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