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.
making just a few. Screw a piece of plexiglass to the bottom of a router
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.
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?
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. . . .
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
OK, so it's not a very good way, but I'm in a strange mood this morning
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.
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.
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:
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
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.
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