Cut Perfect Circles Every Time With This Easy DIY Router Circle Jig

Remove the router base plate

Unscrew the plastic base plate (also called a shoe, running plate, or sub-base) to remove it from the wood router.

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Rip the plywood

Rip a long strip of plywood the same width as the baseplate. Then use the router base plate as a template to lay out the bit location and screw placement on one end of the plywood strip.

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Determine length

Decide how long you want to make your jig. This is the step that takes a little thought and foresight. A 24-in. jig can rout a 48-in. diameter circle and any diameter smaller by moving the pivot location. Make your jig length half of the largest diameter circle you envision yourself cutting plus three inches measured from the center of the bit location mark to the far end.

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Cut the jig shape

If your base plate has a radius, cutting out the shape with a band saw or a jigsaw is a nice touch, though not required. I suggest tapering the length of the jig slightly, as it seems to make it easier to maneuver and reduces the area where sawdust can build up under it. It doesn’t have to be much, just an inch or so along each side from the base plate to the far end.

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Drill all the holes

Drill the holes for the four router screws. Mark the hole placement with a nail set for the exact location. With a counter sink bit, drill the holes from the bottom side of the jig, ensuring they are drilled deep enough so that the screw head is countersunk below the surface of the plywood.

On the opposite end of the jig, still on the bottom side and 1-1/2-in. from the end, drill a 1/4-in. hole to accommodate your 1/4- 20 x 1-in. bolt for the knob.  With the 1/4-in. hole drilled, use a 5/8-in. bit to drill part way through the plywood to counter-sink the head of the bolt below the plywood surface.

Finally, drill out the bit location hole to match the hole in the router base plate. This hole diameter can change depending on the router you have. I used a 1-3/8-in. Forstner bit to drill the hole marked from my router base. This hole allows the router bit to come through once the router is secured to the jig. 

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Soften the edges

Using a random orbital sander, sand back any kerf marks and tearout along the jig’s edge made while drilling and cutting. Then, round over all of the edges, both top and bottom of the jig, using a round-over bit with a bearing installed in your router.

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Wax the circle cutting jig

Use furniture wax to lubricate the bottom side of the plywood jig. This promotes a smooth glide as it rides along the work surface when routing your circles.

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Assemble the circle cutting jig

Set the router base plate aside in a safe location. Attach the router to the jig via the base plate screw holes. You may have to purchase longer screws depending on how thick the plywood is that you used for your jig. Attach the knob via the 1/4-in. bolt hole to the other end of the jig. Ensure the screw and bolt heads are tightened so that they are below the surface of the jig as not to scratch your projects as you rout.

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How to cut circles with a router circle jig

You are now ready to cut a circle using your jig. Here is how to proceed:

1. Determine the radius and center point of the circle you would like to cut on your workpiece.
2. Insert a straight-cut bit into the router.
3. Measure the distance between the innermost part of the straight-cut router bit up the length of the jig, the same distance as the radius of your circle, and mark the position.
4. Drill a hole in the jig at the mark and insert a nail or screw that is the same diameter as the hole. Your jig’s pivot point has now been established.
5. Nail or screw the pivot point fastener into the circle centerpoint on your workpiece.
6. If possible, start and adjust the router in a location away from the workpiece. Use the depth adjustment on the router to lower the bit and make passes of 1/8-to 1/4-in. at a time. Change the bit’s depth with every pass until your circle is routed.If the layout of your circle will not allow you to start and adjust the router in a location where it is not touching the workpiece, you’ll need to do a plunge cut. Plunge cuts are where you start the tool and introduce the spinning bit to the workpiece by plunging it in. To avoid damaging the workpiece or creating a potentially dangerous situation, the router should be started with the bit clear of the material.

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How to cut an arch with a router circle jig

A circle-cutting jig can also be useful when cutting arches. Arches are cut in the same manner as circles, with the exception of where the router bit lands during the process of cutting. When cutting circles, you should place the router bit groove around the outer edge of the circle. An arch, however, should have the groove inside of it. That said, when routing an arch, instead of measuring the distance between the innermost point of your router bit and the pivot point, measure from the outermost point of the bit to ensure it lands inside the arch.

FAQ

How big can I make a circle with a Router Circle jig?

A circle cut using a router jig can be as big as you make the jig. You will need to ensure you can run the length freely. I have seen eight-foot circle cutting jigs to make huge circles.

Can I make a Router Circle jig out of something other than wood?

Yes! Many make their router jigs out of acrylic or polycarbonate. The longer you get with acrylic or polycarbonate, the thicker you will want your materials to avoid it from sagging or snapping in half.