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You can’t put a square tabletop into a round hole, so here’s a circle cutting jig….er…or something like that. This quick jig is perfect for a one-off use and can be built in about 20 minutes. Simple but accurate. It’s easy enough that you could make it every time the need arises. But, it’s sturdy enough to last.
I recommend using a plunge router with depth adjustment with this jig. It makes the process easier, but it’s not required. If you use a fixed base router you’ll spend extra time drilling a hole, setting the router down into it, and removing it to adjust the depth after every pass. Perfectly doable, just inconvenient.
Making the Jig
I used a scrap piece of 3/4” plywood that happened to be the perfect size to cut this jig from. The jig will be made to fit your router, but I’ll give you the measurements for this plunge router. Just remember that you’ll need to adjust accordingly.
Start by removing the bottom plate from the router and tracing it on one end of your plywood. Now, measure from the top of the base drawing to 6” longer than the radius of your circle. If you want to cut out a 5 ft round table top, your radius will be 30”. So, measure 36” from the top of the base and make a mark.
Use something to trace a circle that is smaller than your base (I used a glue bottle). Draw the circle so that the outer edge touches the mark you just made. Use a straightedge to draw lines from the outer edges of each circle and then cutout the jig with a jigsaw or bandsaw.
With a 1/2” forstner bit drill about 1/4” down on each of the mounting holes that were traced from the base. This is just to countersink the screws and washers so don’t go all the way through. Use a twist bit that is slightly larger than your screws to drill the holes through. This will be the bottom of the jig.
Attach the router and make a plunge cut with your spiral bit. If you’re using a fixed base router, loosen the collet until you can pull the bit down to the jig and trace around the bit.
Now you know the exact location of the bit and can measure from the inside of that hole to your radius length and make a mark. Drill a 5/16” hole to act as your pivot point.
I used a 1 3/8” forstner bit to drill out the remaining bit of the area surrounding the bit and then reattached the router.
Cutting Out the Table Top
With your glued up blank face down mark the center of what you want your circle to be. Place the pivot hole over that mark and drill a 1/2” hole. Put a bit of hot glue into the hole and press the dowel in.
I recommend cutting about 1/4” deep at a time. Trying to cut too much will likely result in the bit jumping around and messing up your table.
Slide the jig over the dowel and make passes until the waste is cut away.
Note: Make sure the waste has support as you cut it away.
To finish it off I sand the edges until they’re even and smooth and then round over the edges with a trim router and a round over bit.
You can cutout various sized circles by drilling pivot points in the jig. Mark them with their radius for quick reference.
Now you’ve got a way to cut all the wooden circles you’ll ever need!
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