Best way to cut a circle from sheet?

ProfessorGuy

ProfessorGuy

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I've tried several methods to cut a circle from a sheet, all are unsatisfying. What do the pros do?

I've tried a jeweler's saw, but my 1/8" stock is way too thick for that. You should have 3 teeth in the thickness of the stock, but my coarsest sawblade puts about 12 teeth in 1/8". The sawing is thus very, very slow. After cutting 15 degrees around the circle, I calculated that a full cut would take over 2 hours. And the circle would still need finishing afterward.

I have tried milling 3 shallow blind recesses on the back of a square piece so as to accomodate the 3 jaws of my chuck. Then I mount the piece on the lathe, spin it up and cut with a simple RH cutter. For 3mm thick stock, this does not work well. With my tiny lathe (a Sherline 3"), it took most of an hour to cut a 2" circle from 1/8" thick aluminum. The tool must cut on only one side (or it stalls), so a long series of widening cuts had to be made.

I tried the same trick to mount the piece (on a chuck) on a rotary table on the mill. I can bring the mill up to the edge, then turn the entire piece. Again, 1/8" thick is too much metal to turn through. If I take 0.07mm per pass (this is what my machine seems to like), then 3.2mm takes 46 complete rotations (3312 full turns of the rotary table handwheel). This would be multiple hours to cut a 2" disk.

If the disk is thin, then these procedures would be very easy, except then I'd have no thickness to make the 3 jaw-holding recesses on the back. I guess I'd have to superglue it to a glue chuck.

Please explain to a complete noob how to make a circle out of (relatively) thick stock. Thanks.
 
ProfessorGuy said:
I've tried several methods to cut a circle from a sheet, all are unsatisfying. What do the pros do?

I've tried a jeweler's saw, but my 1/8" stock is way too thick for that. You should have 3 teeth in the thickness of the stock, but my coarsest sawblade puts about 12 teeth in 1/8". The sawing is thus very, very slow. After cutting 15 degrees around the circle, I calculated that a full cut would take over 2 hours. And the circle would still need finishing afterward.

I have tried milling 3 shallow blind recesses on the back of a square piece so as to accomodate the 3 jaws of my chuck. Then I mount the piece on the lathe, spin it up and cut with a simple RH cutter. For 3mm thick stock, this does not work well. With my tiny lathe (a Sherline 3"), it took most of an hour to cut a 2" circle from 1/8" thick aluminum. The tool must cut on only one side (or it stalls), so a long series of widening cuts had to be made.

I tried the same trick to mount the piece (on a chuck) on a rotary table on the mill. I can bring the mill up to the edge, then turn the entire piece. Again, 1/8" thick is too much metal to turn through. If I take 0.07mm per pass (this is what my machine seems to like), then 3.2mm takes 46 complete rotations (3312 full turns of the rotary table handwheel). This would be multiple hours to cut a 2" disk.

If the disk is thin, then these procedures would be very easy, except then I'd have no thickness to make the 3 jaw-holding recesses on the back. I guess I'd have to superglue it to a glue chuck.

Please explain to a complete noob how to make a circle out of (relatively) thick stock. Thanks.
Click to expand...

Is there a center hole? If so you could clamp it between two disks and mount the assembly on a mandrel. Otherwise I'd glue it to a block of wood.
 
Rough it out with a bandsaw or jigsaw, then finish turn the edge with the lathe or rotary table.
 
Could you use something like a flycutter in a pillar drill? I was going to suggest a plumbers tank cutter, which is used for cutting large round holes in copper sheet

http://www.handytools.co.uk/acatalog/Handytools_Catalogue_Tank_Cutters_536.html

But then I realised I did not know whether you wanted a circle of material or a sheet with a hole in it, and as the tank cutter leaves a circle with the pilot hole in the middle, I reasoned that you could use a tank cutter or fly cutter in a pillar drill with the centre pilot drill removed.
Does this help?

Phil
UK
 
If you have a drill press, You can use a common hole saw, you can even do it without the pilot drill, as long as the work is securely clamped down. The cut out disc will be about a ¼" in diameter smaller than the hole saw size. You can clean up the edge of the disc on the lathe.
You can also use an adjustable circle cutter they work well but can be a little tricky to adjust to a high degree of accuracy. Also Be sure to clamp down securely, go slow with the speed/feed and back up the cut with the same material so if it breaks through unevenly, it won't grab the work.
 
FanMan said:
Rough it out with a bandsaw or jigsaw, then finish turn the edge with the lathe or rotary table.
Click to expand...

I don't have those, but isn't a bandsaw blade about the same width as a hacksaw blade? Because my hacksaw blade is way too wide to turn in a 2" diameter saw cut. Maybe at 4 or 5 inches I could bend around the curve. I could rough out increasingly smoother n-tagons, but again, that adds lots of time.
 
How large is your mill? I regularly use my Rotary Table to cut circles out of plate. A good roughing bit can remove a lot of material in each pass.
 
ProfessorGuy said:
I don't have those, but isn't a bandsaw blade about the same width as a hacksaw blade? Because my hacksaw blade is way too wide to turn in a 2" diameter saw cut. Maybe at 4 or 5 inches I could bend around the curve. I could rough out increasingly smoother n-tagons, but again, that adds lots of time.
Click to expand...

My bandsaw is smaller, about a 1/4" wide blade, so it can cut reasonably small radii... of course it's broken right now...
 
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