I tried milling a stencil mask for solder paste today with mixed results. I ended up breaking my only micro endmill (10mil) so that pretty much stopped me right away.
I was milling 10mil brass sheet. I used a helical cutting path 3.5 mil DOC, ~1 IPM feed, 2500RPM. I pretty much took a stab at the speeds and feeds.
It cut about 10 holes before breaking. The holes it cut were *perfect* tho! They matched with the pcb exactly and these are fine pitch SMD pads and some 0406 resistors.
I used the bare side of a pcb as the sacrificial material underneath the brass sheet. I used a test dial indicator to square the machine and flatten the bed to within 1.5mil over the whole board (near 0 deflection in the cut area though, so this wasnt a factor in the break.) The helical motion started above the copper so it wasnt trying to plunge.
I could see that clearage of the swarf is an issue but because its so small its hard to clear eve by forced air. I also had some tapping fluid trying to clear the swarf but I think that made it worse as it collected near the bit instead of getting kicked clear when it was cutting dry.
Anyone have any suggestions? These tools are about $20 each...so expensive for a trial and error strategy!
Colin