# Best way to cut a circle from sheet?



## ProfessorGuy (Feb 12, 2015)

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.


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## John Hasler (Feb 12, 2015)

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.
> 
> ...



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.


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## FanMan (Feb 12, 2015)

Rough it out with a bandsaw or jigsaw, then finish turn the edge with the lathe or rotary table.


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## hermetic (Feb 12, 2015)

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


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## Eddyde (Feb 12, 2015)

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.


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## ProfessorGuy (Feb 12, 2015)

FanMan said:


> Rough it out with a bandsaw or jigsaw, then finish turn the edge with the lathe or rotary table.



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.


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## kd4gij (Feb 12, 2015)

This is what I use.
http://www.ebay.com/itm/NEW-NIP-GEN...440?pt=LH_DefaultDomain_0&hash=item19fb453228


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## buffdan (Feb 12, 2015)

Ditto on what Hermetic and Eddyde suggest.
Google trepanning tool:  https://www.google.com/search?q=tre...=X&ei=xxXdVMKaK8GcNsrCgNAL&sqi=2&ved=0CCcQsAQ
I use a Valcut tool, works fantastic for a hole, or for cutting out for a disc, depending on the cutter.

Dan


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## Pontiac Freak (Feb 12, 2015)

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.


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## FanMan (Feb 12, 2015)

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.



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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## raven7usa (Feb 12, 2015)

Another thing you could try: Use double stick tape on a faceplate to hold your part. If you don't have a faceplate, use a piece of wood in the 3 jaw chuck a backing plate then use the double stick tape. Use a small object held in place by your center in the tailstock to put pressure on part to hold it tight against the tape. Cut out your part to size. The thickness of the tape should give just enough clearance for your tool not to hit anything it's not supposed to. This way you'll not have a hole or any marks in the center of the part.


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## mattthemuppet2 (Feb 12, 2015)

if you can fit the sheet into a 4 jaw on your lathe, use a trepanning tool (look up some pics online for how to grind one). I've managed 3/8in (or 1/2in, can't remember) on my tiny lathe without too much trouble. It's not fun, but it works


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## kwoodhands (Feb 13, 2015)

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.
> 
> ...




Several ways will work.Cut the piece out with a holesaw that is oversize. First remove the pilot bit if you do not want a center hole.Then glue the piece to a piece of 3/4" mdf that will go in the chuck.I would use hot hide glue because it will hold and a heat gun removes the piece in a few seconds.Yellow carpenters glue will work too with a piece of brown Kraft paper between the mdf and the work.When done turning the edge to dimension the work will pop off with a screwdriver.If you have hot hide glue it is easier to clean up ,just warm up the work and scrape the residue off.Hot water removes the gummy residue that is left.
Trepanning will work too.Glue the piece the same way as the above method.
Your lathe should be able to handle either method.

mike


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## Luminast (Feb 13, 2015)

ProfessorGuy said:


> 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.



Using the lathe seems to me like the best solution.  The motors on those lathes are really small, but something is wrong if your lathe will not cut aluminum without stalling.  Are you sure the cutter was sharp, and properly ground? Did it have enough end relief to prevent the bottom edge of the tool from dragging on the outside radius of your cut?  I'm not handicapped by such a small lathe motor, but I've cut many circles out of aluminum by hot melt gluing the stock to a face plate made out of plywood, or MDF, and turning the circle on the lathe with fast and easy results. Or make an aluminum face plate that is slightly smaller than your finish diameter. 

I would grind a 1/16" wide cutting tool out of a piece of 1/4 x 1/4 steel so that the end looks rather like a 3/16" or 1/4" long parting tool.  As you probably know, the end relief angle you would need depends on the diameter of the circle being cut.   If my math is right, you need at least a 25 degree end relief angle, if there is no side relief.  Side drag on the cutting tool can also rob your lathe of scarce power, so you can grind it with a tiny bit of relief behind the cutting tip, if needed.  Feed straight in.  If that's still too much load on your lathe, you can try narrowing the cutting tool even more to perhaps 1/32".  If the tool is fed straight in, it should still be plenty strong enough to cut aluminum.  I've bored the inside of tiny and shallow holes in steel with such a dinky cutter.  To cut aluminum, you don't even need HSS.  You could grind a functional cutter out of a piece of 1/4" key stock.

You might also try using a cutting fluid.   A good cutting fluid for aluminum is one part of any light weight machine oil, like 3-in-1, or any 10W oil, thinned with 3 parts of mineral spirits.  That might help a little.


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## Fabrickator (Feb 13, 2015)

I found myself faced with a similar problem some time ago on a project that I was working on.  I needed to accurately cut 4 - 3" OD X 2" ID circle plates out of .060" thick aluminum. I started by rough cutting the OD's on my floor standing band saw. I trued and finished sizing the OD's by making a disk/sandwich jig to run on the lathe.  I then cut the ID's on my woodworking Jig Saw sandwiched between 2 pieces of hardboard.  It was like riding a mad bull trying to keep control of them bouncing around when the blade would catch, but I muddled through at my neighbors expense (noisy). I rough finished the ID's with a large sanding drum on my drill press. Then I finished sizing the ID's by holding the parts individually on my lathe by the OD.  I tried using hole saws for a couple of these operations but all it wanted to do was burn it's way through. 

It was a lot of work and I remember thinking how there must be a better way, but I couldn't figure out any other way to do it.  Thin stock is hard to work with anyway you try to do it short of plasma, flame or CNC.


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## Bakkskive (Feb 13, 2015)

I made some round plates for an IED housing (yes, the dangerous type, for scientific use) when i was an apprentice and my master taught me a method that i like to use.

He used two aluminum discs cut from round stock, one set up in the chuck and one loose with a center hole drilled. Both with smooth, dry surfaces and an OD close to the desired measure, as big as possible in other words.

Sandwich your plate to be cut between them, clamp them securly together with the rotating centre and turn to diameter.

Im not at my shop now, but i can take pics later if you want.


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## RJSakowski (Feb 13, 2015)

[FONT=&amp]You didn't say if your piece has a central hole in it  or how true the finished circle had to be.  Since you were initially cutting with a jeweler's saw  it sounds like you had to do some cleanup work.  There are two methods to rough out a circle that I have used. one is to cut out a square using a hack saw or band saw, then cut the corners off to make an octagon.  If you want to get closer yet, you can cut the resulting eight corners.  That should bring you fairly close to your desired circle.  The second method is t scribe a slightly larger circle  on your workpiece and drill a series of not quite intersecting holes on the scribe line.  With a 2" circle, you could rough out the part with about 25 holes.  You can then use your jeweler's saw to connect all the dots.  I have also used an old drill bit in a hand drill to complete the parting by angling the drill bit in the holes to connect them.  Either way is fairly quick.  I have used both on steel plate  over 1/2" thick..[/FONT]


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## pdentrem (Feb 13, 2015)

Bakkskive said:


> I made some round plates for an IED housing (yes, the dangerous type, for scientific use) when i was an apprentice and my master taught me a method that i like to use.
> 
> He used two aluminum discs cut from round stock, one set up in the chuck and one loose with a center hole drilled. Both with smooth, dry surfaces and an OD close to the desired measure, as big as possible in other words.
> 
> ...



I use something similar. The driving surfaces are covered in cork and using the tailstock to sandwich the part to turn the OD. Look at videos showing metal spinning. Same way of doing it. 

Remember that you can not take heavy cuts. Doing so will either stop the disk turning or the tool will cam it out. Use lots of lube at the cutter to prevent the chip sticking to the tool.

Since the part is Al, do you have a table saw to rough it out? Use a Non-ferrous metal blade to at least cut off the corners. I usually shear off the corners or if it is a casting and rolled to size, I use a round mold and roll it down to size while rotating the part 90 degrees at every pass.
Pierre


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## Bakkskive (Feb 14, 2015)

Hi, i decided to make a youtube-video of my way: 




If i feel brave at the moment i dont bother rough cutting it first and just turn it down from a full square, but it sure makes a lot of noice.

Tommy


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## shorton (Feb 18, 2015)

Tommy, Nice how-to.  Agree, screaming success.  For the larger diameters, I assume you change the "clamp" on the chuck side, too.


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## Bakkskive (Feb 19, 2015)

Yes, i use a larger clamp piece too. As close as possible to the diameter to be cut.


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## Gerry (Feb 24, 2015)

I stick the sheet metal to my faceplate with double sided tape then cut the disc with a sharp lathe tool


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## ProfessorGuy (Feb 26, 2015)

Thank you for your suggestions.  I didn't realize there would be so many answers!

 I ended up milling around the edge on the rotary table (mounted from the back in a chuck on the table).  Then I cleaned up the edge and put in a 45 degree camber on the lathe.

I used an endmill to put on the design (the initials V.C.), painted, then sanded the surface.  I filled the 3 indentations on the back with magnets, so this is a fridge magnet that can hold 10 pounds.


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## jdedmon91 (Jul 21, 2019)

It depends on the thickness of the sheet and can it have a center hole. I’ve put center holes in flat sheet and stop signed the OD and turned it round off of an arbor. I actually used this method to do a steel plate to mount to a backplate to make an drive dog plate a while back


Sent from my iPhone using Tapatalk


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## Latinrascalrg1 (Jul 21, 2019)

jdedmon91 said:


> It depends on the thickness of the sheet and can it have a center hole. I’ve put center holes in flat sheet and stop signed the OD and turned it round off of an arbor. I actually used this method to do a steel plate to mount to a backplate to make an drive dog plate a while back
> 
> 
> Sent from my iPhone using Tapatalk


Check the date on the thread.....
Dont think the op is still stuck on this project although I could be wrong!


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