how do i make a square copper plate round?

I need to end up with a piece of 3mm copper plate 4" diameter, flat. Obviously it needs to be done in the lathe but I cant think of how to hold it? Ireas greatly welcome.

Scrap ply or MDF on your faceplate, few bits of thin double sided tape for friction and then use a pressure pad to push the disc against the faceplate with your tailstock. Rough cut it first so les sto machine off.

Pressure pad can just be a bar end of say 2" dia, faced one side and Ctr drilled the other.

Edited By JasonB on 28/10/2017 09:42:34

Make two pieces od wood a little inder 4" diameter. One about 1" long with a centre hole drilled into one face. The other long enough to fit in the chuck with about 1/2" inch sticking out. Face the end of this piece when mounted in the chuck. Place the copper sheet between the two pieces of wood and apply pressure to the centre hole in the thinner piece using a LIVE CENTRE. Apply as much pressure as you think safe from the tailstock. Turn the square sown to a circle wsing a very sharp tool and taking light cuts. I would first cut the corners off the square to make it into an octagon. You could also put some double sided adhesive between the wood in the chuck and the metal.

Les.

Edited By Les Jones 1 on 28/10/2017 09:49:06

Hold it in the four jaw chuck with the jaws reversed and cut a disc out of it using a trepanning tool - a piece of HSS ground like a short, thin parting tool with extra clearance on one side to allow for the curvature of the cut.

But copper can be kind of grabby, so maybe try one of the above ideas first.

All of the above will work - but another variation would be to drill holes in the corners, screw it to a wooden plate (which is bolted to the faceplate) and trepan the piece out.

Regards,

IanT

If you can, saw it as close to a circle as possible first. If it is later going to be drilled (for tubes etc) then drill these holes first if they might help you to grip it (e.g. using screws into a wooden faceplate). IanT's approach sounds good, might be safer if you use double-sided tape or superglue to hold the centre portion in place so it doesn't spring off the lathe as you cut through.

I cut a 4 inch circle out of 1/8 aluminium by making a trepanning tool adaptation of my big boring head, then using it on my mill, clamping the ali on a bit of MDF with strap clamps. As ali is similarly "grabby" to copper this might also work (also indicates that it would work on the lathe faceplate).

Re suggestion from IanT about holding the copper onto a wooden plate with screws. Idea works but use 8 rather than 4 screws. Double sided tape underneath helps too. Also make sure the wood is nicely flat. Ex kitchen cabinet or similar MDF (preferable) / chipboard is better from the flatness point of view.

I use similar methods a lot for sheet metal jobs on a pillar drill and milling machine. Pays not to under-estimate the tendency of the material to grab and climb away from the backing plate. Anything much over 1 1/2 inches between fixing points can be risky. No idea of the proper engineering considerations but I've never had problems with that sort of fixing spacing but I have sometimes hit trouble with them further apart. Much easier to add a few screws than to start over! With the close spacing holding just round the outside is will be fine.

Clive.

https://youtu.be/0DrI5B4hui0

If you click on this link it'll demonstrate the ideas put forward of holding the square piece into the lathe, to turn it to size, it also demonstrates the dangers of doing such work. There's two ways to do it, so I'll leave it to you to watch the video and decide on the safest method. To me removing as much material first and taking the piece to final dimension on the lathe is by far the safest than a jagged piece of metal flying out the lathe.

Edited By Jon Cameron on 28/10/2017 11:08:05

Why on the lathe; what's wrong with marking out and sawing/filing to shape?

Andrew

I'm with Andrew, electric jig saw with a fine tooth blade. Set on workmate with small gap between jaws to support the plate and away you go.

If you have a horizontal/vertical band saw, use the saw in the vertical possition, cut close to the line, very little finishing should be required.

Ian S C

If you use JasonB's method I suggest sawing it to near net shape first. If the part is trepanned out of the square while on the lathe you would have the outer part flopping around when you cut through. Kind of dangerous.

Thanks all

I had intended to experiment with the clamping method, cutting very close to shape first. I cut a lot of copper sheet on the bandsaw for boiler end plates and contrary to what one would expect have found on my band saw that fine tooth blades very difficult to work with whilst coarse tooth blades work very well. By fine I mean 18 tpi and course 6tpi but I guess its all down to the speed of the cut and thickness of plate. Thanks everyone for their valuable input.

Nigel (Pendle Steam Boilers).