Help machining copper sheet

[fastturbovet]

I have a CNC router that was built from a CNC adhesive dispenser. I have a Rotozip as the power which runs at 30,000rpm.

I am trying to cut shapes in .020" copper sheet. The shapes are 2D but have some relatively complex curves and interlocking pieces. I would really like to use a 1/16" bit because that's the size my cutout pattern was designed for. I had a couple of 1/8" mills and a couple of 1/32 mills, but I quickly broke the 1/32" mills. I am going to get a 1/16th to try it out, but can anyone give me some ideas on how to do this effectively. What feedrate should I run? Should I try to cut through the whole .020" at once or is that too much? I tried a high feed rate for Aluminum and it killed the bit pretty quickly.

If it matters, it seems to have much more trouble plunging through the workpiece than actually doing the cutout. I broke the 1/32" bits that way, they deflected upon moving down in Z into the sheet and just snapped.

I am mounting the copper with sticky tape to a block of dense form (rigid) and sticking that to the table with tape. There is no apparent movement in the sheet when it's being machined and the cut lines are nice and smooth WHEN it works.

I think (guessing) the problem is the copper is so soft it's gumming up on the bit. Do I need a MUCH lower speed to do this right? If so, what RPM should I look at? A few times I seem to have gotten magical feed rates which have produced great cuts, but 99% of the time I dont get that. Is there anything I can put on the piece to help prevent the problems, some sort of lube?

Thanks!

[murphy625]

You need to cut at low speeds..

Yes.. copper is gummy.. I've done enough drilling and tapping on it.. Lots of coolant or oil and keep it slow.

I am no machining expert by any stretch.. But the problems your having seem to be the same mine were..

Keep the copper cool.. Not sure but I would bet the colder the better..

Keep the tool slow and make sure chips have a good exit. I would actually clean my drill after each hole because there would be a small build up of copper around the cutting edges. Probably a result of not being able to remove enough heat?

I think your on the right track..

Murphy

[psychomill]

Use coolant! .020 copper sheet is probable dead soft. Not necessarily though. Can you slow down the RPM? Depending on the model, I think you can at least get down to 12-15k with a switch. Be sure to use a 2 flute endmill with a standard helix (30 deg). The hi-helix will probably cause problems with the tape down set up and coolant. If you can't run flood coolant, at least get a good spray bottle or set up a mister with heavy flow. Take the whole .02 at one shot and start your feed around .0025 - .003 per tooth. Don't use oil though for your case unless you can thin it out a bunch. Oil tends to be thick which normally would be a good thing. Problem is that your chip thickness is small so it wads up on the cutter. If you can, get a TiCN coated carbide endmill. HTH