Advice needed for cutting copper

[johnm]

Folks -

Okay, next! Still don't have the material to cut the branding iron job, but had another one project come my way... Copper!

I have a prospect that wants us to cut out jewelry bangle blanks with engraved lettering. I am using some scrap sheet copper, I don't know what gauge it is, it's just shy of 1/32" thick.

Anyway, what would you recommend for cut feed speeds and a bit? I need to cut out an oval approximately 1" x 2" and I am going to * try * using the vacuum hold down for it. How much should my stepdown be on each pass? From my earlier post re machining aluminum and brass, .4 to .7 is what I was going with for feed speeds, and .1 .2 for z moves. I was going to use a 1/4" end mill for cutting and a 90 deg vee bit for the engraving. If any of this is a huge red light, please holler! I'd really like some idea of a prudent step-down rate.

As always, thanks in advance, at the time, in arrears....

John & Rose

[paco]

Lube (not flood), low RPM, conservative (cautious) feed, not too enthusiastic stepdown (try 0.02" first). The above feed sound good to get started. V bit might be the challenge; don't chuck in the one you prefer... No HSS tooling above 5000-6000 RPM. Blow the chips from the kerf often. Keep the S key handy!

Keep us post on the results.

[johnm]

Paco -

Hey buddy! Well, *parts* of this worked... We used a 60 deg Vbit for the lettering and a 1/4EM for the cut-out.

Our feed metrics were .5 X/Y and .1 Z with a .010 stepdown at 10k rpm for both engraving and cutting. Initially, I tried a vacuum hold on the part, but the vacuum surfaced area was just too darn small. We used carpet tape and it worked fine.

I removed the dust shoe for better access, and gave the surface of the material a spray of WD39... it was a *really* old can... but was careful to keep the spray off of the carpet tape.

The engraved text was just too small to be legible at .010 deep, even at .005... The copper becomes proud around the engraved area - with a larger text or image, it would probably be okay.

Cutting the part out went well. The edge was resonably clean and another squirt of WD39 released the adhesive without any gumminess on the component.

In evaluating things, I think we could cut the parts out, but don't think engraving such a small image would work.

John

[paco]

V tool bits aren't really meant for metal, check for engraving bits... generally smaller (1/4" CED) but well sharp up to the point. You can choose 'em true point or flat point/tipped off and have a wider choice of angle.

[johnm]

Paco -

Perhaps a pointy engraving bit would do it - we have the one we got with SB's bit package and it has about a 1/8" diameter tip on it.

Got a part number?

TX

John

[bleeth]

John: For a great conversation and all you will ever need to know about engraving bits for your bot call bits and bits in Oregon (1-800-972-7081).

Dave