Best drill type for copper
We machine alot of copper, not sure what grade, I know some of it is Class C. i have been using brite finish drills and black oxide drills without a whole lot of success. The diamaters are 1/8th, 3/32nd and 7/64th. Anyone recommend a drill type and SFM for drilling copper?
I have been using the cobalt split point drills for drilling copper. Plenty of coolant, using a short advance and back out to clear the work. If the drill should make any noise, stop and install a new drill. The drill used is a 3/16" and going about 1-3/4" deep. Other holes are a N0. 50 drill and drilling 3/8" deep. I use about a drill diameter for each step in depth.
It's a matter of combatting the tendency to bind because of the gummy material combined with the abnormally high rate of expansion with increasing temperature. Coolant is obviously crucial, as noted by the first respondent.
You need higher than normal relief angle, bright finish not black, and (if you can) thin webs and narrow margin lands. Definitely go with slow speed and heavy feed regardless of drill geometry.
Another thing which helps if drilling from the tailstock of a manual lathe, where excessive backlash can present a problem with grabbing: slow-helix drills (ie straighter flutes than usual).
If you can't source such drills and have grabbing problems, it could be worth stoning an axial land (equivalent to zero top rake in the lathe tool analogy).
It doesn't have to be very wide to make an appreciable difference, but does need to be very smooth.
Well, this may not be the most orthodox method, but if the tolerance doesn't matter that much on the diameter of the hole, I just grind the drill off center a little. Deep holes are awful in copper, but they are often just for water passage. Grinding the drill off center will make it walk just enough to keep the hole from squeezing up on the drill.
Regal13 nailed it.
I do the same thing when drilling Aluminum-Bronze.
Make the drill a little offcenter, so the hole won't bind.
I never thought about doing that for aluminum bronze material--I always just stoned my drill to ease the sharp pressure angle to keep it from trying to bite into the material.
I have had a fair bit of luck on gummy materials by dulling the drill edge just a bit. Usually I will take a 400 stone and just hit the egde a few times till i see it break over.