Which Technique to Cut Circle?

[Mike Gottlieb]

I have to cut a 30" circle from glued up boards. I plan to use a circle cutting jig with my router. My question is which technique is better: 1. Use a 1/2" upcut solid carbide spiral bit and take progressively light cuts until the circle is completely cut through; or 2. Use a jigjaw to remove excess wood close to the edge and then use a flush cutting bit to bring the circle to the desired size? I am somewhat concerned about chipout. Any advice would be appreciated.

[Angie Orfanedes]

I just use a router with a compass jig and take about 1/8 inch to 3/16 inch at a pass - this has always worked well for me. I have heard others take one light pass with router (say 1/8 inch ), and then cut in the groove with a jig saw, and then finish off with router.

[Mike Henderson]

I always rough cut with a bandsaw or jigsaw first, but I leave enough that it may take me two cuts with the router to bring it to size. I usually use a spiral upcut bit. If you're going to keep the circle (like a table top), there's the issue of the center hole.

I have a MicroFence jig and really like it.

Mike

[Myk Rian]

How thick is the glue-up? If it's more than an inch, do what Angie said. A light pass with the router, jigsaw it, finish with the router. Otherwise, just use the router.

[Jim Kountz]

If you dont want a hole in your finished piece, use double sided tape and fasten a small block of wood the workpiece. Drill your center hole in the block. You will have to also tape a block of the same thickness on the arm of the compass jig somewhere near the router so it doesnt want to tip. After you make your cuts just pop the block off and you're done.

[Joel Goodman]

Rough cut with a jigsaw and then use a jig and a router with a straight or spiral bit. You can make one with scrap plywood which replaces the router base (use the orig as a template to locate the screw holes) and then extends long enough to act like a compass. If you put the hole for the pivot on the bottom of the tabletop (or whatever you're making) and don't drill the hole all the way through your top you're in business. The quality of the cut is excellent -- obviously take normal precautions as to how much depth you cut --- take a few passes. Takes longer to describe than to do.

[Grant Vanbokklen]

Do you not have a band saw? I would suggest using a circle cutting jig on the band saw.

[Philip Duffy]

When I did mine several years past, I did it from the bottom and the router compass hole it still there, I suppose. Make it an easy job and do 3 light passes. Phil BT

[Guy Belleman]

Watch this video. This method is much quicker and safe with the sled. http://www.metacafe.com/watch/432752/circle_cut_on_a_tablesaw/

main website for this gent is: www.woodguy.com

[Joe Scharle]

I use your method 1. Eliminates registration difficulties, gives a clean edge on both grains. However, it is dusty without good DC on the router. I've never had anyone look under the top and say, "What's that hole?"

[Prashun Patel]

+1 Compass jig and router. You can make a jig out of 1/8" hardboard screwed to the base of yr router. Plunge through the board with yr spiral bit.

If done it with a straight bit, but the cuts can get squirelly around the end grain. I found it best to do the end grain quarters as climbing cuts (clockwise) if you use a straight bit.

If you use a good spiral, you should not have this issue and you can do the whole thing counterclockwise and safe.

I also wouldn't worry too much about upcut or downcut if you're planning to ease the edge after anyway.

[pat warner]

Near zero risk?
Make a templet of said diameter out of MDF first. Verifies all your arithmetic and method.
Clamp templet to work and plunge rout the sample in stages.
No holes to drill in the work.
You can also avoid the pre-jig/bandsaw step with templet approach.

[Michael Panis]

Watch this video. This method is much quicker and safe with the sled. http://www.metacafe.com/watch/432752/circle_cut_on_a_tablesaw/

main website for this gent is: www.woodguy.com
Hmmm...Seems like an easy way to lose a few fingers. I'm sure the Wood Guy knows what he's doing, but I wouldn't want to try that technique myself.

[Jim Kountz]

I've never had anyone look under the top and say, "What's that hole?"

Thats assuming its for a table top. The OP never stated thats what this was for. Ive had the occassion where the said circle would be seen from both sides so therefore a hole wasnt an option.

[Chris Padilla]

Jasper circle cutting jigs are sweet...I own several of them. For a 30" disc (circle), you'll want their #300.

Just google "jasper circle cutting jig" or "jasper jig 300" and you'll be on your way.

These use a plunge router.

Also, if a pivot hole is a bother, get Japser's pivot plate (part #350) and you can carpet tape it and buzz away.

[Mike Gottlieb]

Many thanks guys. It will be for a table top, so pivot hole won't be a problem.

[Greg Crawford]

Spiral bits work well, but there are some differences. A down-cut bit gives the best finish on the side the router is on, but won't clear chips very well, so very light cuts are a must. An up-cut bit is agressive and clears chips well, but leaves a rough finish on the side that is up during routing. If you're doing the table top upside down, an up-cut bit should be great. I'd use a 1/2" shank, and at least 3/8" diameter to handle the workload. Take shallow cuts at first to see what the bit will handle. Most bits should never be used for more than about 1/2 of their diameter in each pass, but I've found that in most cases an up-cut can easily handle a depth equal to it's diameter. A plunge router works well by using the turret stops for successive passes.

[Joe Scharle]

Thats assuming its for a table top. The OP never stated thats what this was for. Ive had the occassion where the said circle would be seen from both sides so therefore a hole wasnt an option.

Jim, I stand corrected. At 30", I assumed table top.

[Jim Kountz]

Heck Joe you may be right, we still dont know for sure yet!!

[Chris Padilla]

Heck Joe you may be right, we still dont know for sure yet!!

Yeah, we know for sure I think:


Many thanks guys. It will be for a table top, so pivot hole won't be a problem.

[Jim Kountz]

Well now there ya go.

[Rich Wedler]

Thanks Mike. Our Circle Jig features the micrometer dial which provides a means of measurement and/or adjustment. This makes the jig unique for producing even the most demanding of cuts like those required when cutting mating radii (as in the case of a surround of solid stock around a plywood or composite table top). We also have several accessories for the Jig which increases your options.

A few links that might help for cutting circles:

Cutting Large Radii (http://microfence.com/large-circle-projects-i-22.html)(a look into how we use the jig to make a circular bookcase and a composers desk)
Circle Jig Video (http://microfence.com/video-i-6.html#circle_jig)