Strategy for cleaning drilling / slotting copper bus bar

Hi Guys,

We make various little bus bars that go in our products. 10's per year of about 10 different part numbers. Normally something like 1/4" thick 110 copper and we need quarter inch clearance holes (0.257" diameter) or slightly slotted holes (0.257 hole elongated 0.125"). Occasionally we have tapped 1/4"-20 and 3/8"-16 holes.

This is the only copper I have ever machined and it has always comes out a mess when drilling. Terrible burrs. Once I get rid of the burrs, no problems tapping.

I have good VMC with flood cooling and 12k spindle. What sort of strategy would you recommend for tools and tool paths / and speeds and feeds to make a clean hole? Since low volume, I don't really care too much if it takes 2 seconds or 1 minute per hole.

Thanks for your advice,

-Jim

An update:

I've previously made these parts on a CNC knee mill with mist coolant. They were always a gnarly mess. Hence the reason for my question.

Read through a bunch of previous posts and there were a few that mentioned just doing it like aluminum. So I did. Just used the default cutting conditions for aluminum. Helical bored (Mazak "tornado" cycle) the holes with a 3/16" 3 flute carbide end mill at my max spindle speed of 12,000 RPM. Flood coolant using Trimsol at 5%. Holes came out beautiful. Little flap of aluminum at the bottom and little edge pushed up at the entry. Both easily clean off with a the deburr tool while the next part runs.