Cutting .020" brass??

[cnc_works]

I'm quoting a job to cut .020" brass sheet into very small parts, picture a rectangle 2.5" x .5" with a 1/8" hole in it and filleted corners. My test cut was at 20ipm, 15k with a 1/8" 0-flute up-cut Onsrud ramped with a .01" cut step. Held down with double sticky pretty successfully.

It came out pretty clean but had a little edge burr here and there maybe smeared or ???. Any input as to which direction to go for the next test?

Thanks guys
Donn

[Brady Watson]

Donn,
Be more specific about the edge - is it faceted like the edge of a dime or is there a little sharp sliver of metal sticking up somewhere? Explain the 'smear' - is it from the tape or are you referring to a metal smear?

-B

[cnc_works]

Metal smear Brady. Kinda like the burr you get when you sharpen a chisel. As far as the quarter $ milling effect, its fine.

[Brady Watson]

Smear usually indicates overheating. You can either increase the chipload or use a coolant. Increase the chipload by lowering RPM or speeding up move speed. You may not be able to speed up move speed if A) Your design is very intricate and there isn't enough room to actually run at that speed or B) Too much force is being applied to the part that it causes hold-down failure.

If running coolant, compressed air using a few brass fittings and a football inflator needle with the safety hole taped shut works well. Shoot it at the bit itself at 20 to 30 PSI. If you have a cold gun - even better. The other option is to manually mist on alcohol while it is cutting to cool things down. The key word here is 'mist' - don't flood it or you might make the tape fail. Denatured is best, with rubbing alky being 2nd choice.

-B

[magic]

Could also possibly be the upcut bit.

I usually use a 3/16 4 sided carbide at a slow feed

You can also use a hand-held deburring tool, if that's what the customer wants.