What to use to cut 12" circles?

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What kind of tool can I use to cut a 12" circle from plywood? These need to be as close to perfectly round as possible. I have quite a few of these to do.
I don't have a disc sander or a bandsaw for this. I have used a fly cutter for smaller stuff, but I wouldn't want to use a 12" fly cutter if they even make one.
Brian Elfert
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<< What kind of tool can I use to cut a 12" circle from plywood? >><BR><BR>
Router with a circle cutting jig.
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Brian Elfert wrote:

with a 1/4" sprial cut bit. Measure form the outside of the router to a spot 6" away on the plexi and screw it to the center of the circle.
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You can do it with a jigsaw, scrollsaw or a router. You could probably get a nice clean circle using a beltsander on it's side and a jig (after rough cutting them). Maybe you could toss a stack of them on a lathe. Table saw might work ok if you cleaned them up afterwards. What tools do you have?
JP
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Brian Elfert wrote:

http://www.woodworkingtips.com/etips/etip102000sn.html
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It depends a bit on the tools that you have. The easiest tools with which to work accurately would be a table saw or a router. Both of these will require a small pivot pin hole in the center of your finish disk.
Table saw method: If you already own a sled, great. It does not matter whether it is one sided or on both sides of the blade. The center of the disk that you want to make needs to be the radius distance away from the blade. Square cut all your disks first. Install the sled. Tack the piece to the sled with a pivot pin ( I usually use a #4 finish nail on 3/4" material) Turn the square's corners off the edge of the sled and cut them off, repeat until you have an extremely rough beginning of a circle. Turn the disk in a circle where the high corners are just bumping the blade, move the sled forward slightly and repeat until you get to the full diameter. You will get really true circles with reasonable finish. This method is faster than working with a router in my opinion, though I have both.
Router method #1: Mount the router to a scrap of material. 1/4" Plexiglas or plywood comes to mind. You can remove the router's plastic base and reuse the machine screws to hold the base on the ply strip. Run the router bit you intend to use through the ply. Measure out the radius amount and tack onto your disk material at its mid point. You will have to adjust the router's depth of cut 3 or 4 times for 3/4 material, but you can get extremely accurate disks.
Router method #2 If you have a router table, combine the thoughts from 1 and 2.
Hope this helps.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Keep the whole world singing. . . . DanG

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DanG wrote:

Finish with a stationary belt or disk sander, with a similar jig, for a sweet-looking finish.
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http://pages.cthome.net/edhome
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Brian Elfert wrote:

It would help if you said what tools you _do_ have.

--
--John
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I have a router, shaper, table saw, drill press, and scroll saw.
Brian Elfert
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Rough cut the circle oversize on the scroll saw. Drill a hole in the middle of the piece the same diameter as the arbor on your table saw and mount it on the saw arbor. Lower the blade height adjustment until the entire workpiece is below the table. Take a sheet of 36 grit sandpaper and lay it grit-side down over the blade slot. Back it up with a piece of 3/4" plywood. Now turn on the saw and slowly raise the blade height adjustment. The sandpaper will grind the edge of the workpiece into a perfect circle.
OK, so it's not a very good way, but I'm in a strange mood this morning :-)
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For one thing, I can't have a 5/8" hole in the center of the circle. A small hole would be fine, but not 5/8".
I'm thinking about a Dremel or Dewalt cut-off tool with a circle cutting guide. About $80 total.
Brian Elfert
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In case it wasn't obvious, I was only joking. What I described is an entry for the Darwin Awards, not a technique I was seriously suggesting you try.
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Roy,
LOL You had me going there for a moment. I could just picture a piece of plywood spinning four thousand RPM's and out of bounce.
Gary
writes:

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Ooops, make that out of balance. (No problem with it bouncing, all over the shop.)
writes:

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writes:

Unless you have other uses in mind for either the Dremel of DW imo a circle attachment for your existing router would be a better buy.
As I have a router table with a miter slot I have a scrap miter bar with small screw that sticks up as a pivot, I put a stop at the requred radius for the bar and then I can feed the work into the router.
You didn't say what thickness of ply you are working with but I found the Dremel and similar size tools under powered for most any wood working job unless using very small bits and/or very light cuts.
Bernard R
Bernard R
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Brian Elfert wrote:

Somebody already mentioned a circle cutting jig you can make out of scrapwood to use with your router, so there is no need to shell out $80 for one. If you don't want to put any holes in your circular pieces, you could temporarily glue on a scrap block that would hold the pivot hinge. I made a rough drawing showing what I mean. It's not to scale, and you'd probably want to include some washers and glue up a strip of sandpaper between the pieces to keep it from slipping, but should be good enough to give you an idea:
http://www.skunkduster.com/woodworking/circlejig.gif
Good luck! -Rick
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On Mon, 10 May 2004 19:58:56 -0700, Rick Nelson

Why not make a larger cutout from scrap, for which you can use a center point. A bit of careful sanding, then use that as an outside template for the router.
Bill.
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Brian Elfert wrote:

Router's the obvious choice. Quick and dirty, find a scrap of something long enough to serve as the circle guide and not too thick (piece of 1/8" Masonite for example). Pull the plastic shoe off the base of the router and use it to mark where you need holes in the new guide. Drill the holes including the center hole (hole saw or Forstner is handy for that), countersink the screw holes, screw the guide onto the router. Measure from the edge of the bit however far you need to go to put your pivot hole--if you're making a disk then measure to the inside edge of the bit, if you're making a hole then remember to subtract the diameter of the bit. If you can afford a hole in the center then drill one and drop a drill bit or nail or whatever into it to act as a pivot. Cut--if you're cutting a disk go clockwise, if a hole then counterclockwise. You may need to make several passes.
If you can't afford a hole in the center then use a piece of scrap and stick it down with double-sided tape.
From here you can get as fancy as you want.
If you've got the edge guide for the router you can make a piece that clamps down on the guide-rods and has a projection that fits in your pivot-hole.
The Rotozips and the like work very nicely for plaster and drywall, but the bits they provide for wood aren't all that good--they cut slowly and tend to flex, not to mention they're down-spiral not up-spiral, so they tend to push the dust into the groove instead of pulling it out. I haven't tried a quarter inch spiral cut router bit in the Rotozip--if it's got enough power to swing it it might work nicely.

--
--John
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Router with a circle cutting base.
John

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