Reposted from my work blog.
Drilling Aluminum – How not to break drills.
OR Rebonded Aluminum
Machining Aluminum is great, right? It’s easy to work with, cuts easily, and is inexpensive to buy mail order because it’s light, which cuts down on shipping costs.
It has nice material properties and is generally a favorite in machine shops.
So why is it so terrible to drill small holes in? Why do tiny drill bits even exist? They’re like an exercise in frustration. They break super easily, it’s hard to spin them fast enough, etc.
How does aluminum drilling go wrong?
Column bending and buckling. The drill goes in part way, some chips come out, and then for some reason the chips stop coming out as well and the drill bit just snaps right off. This is due to inadequate chip breaking. In order to move the chips up the flutes of the drill, you need to make them smaller pieces. This is done by a quick retract of the drill so that the chips move out of the hole.
Rebonded Aluminum This can be caused in two different ways. Very small, powdery chips are produced by drilling with a low feed rate. Those chips are hot due to friction with the cutting tool, and they’re small, so they get close to their melting point. Those melty chips stick to the steel or carbide tool, and weld themselves on there. Now the tool is a steel/aluminum system instead of the original steel, so it doesn’t cut as well. This is often the cause of broken tiny drill bits in aluminum.
So what are some solutions?
First – proper speeds and feeds. If you’re running a manual machine and controlling the feedrate by hand, you need to match your feedrate to the drill RPM to get a proper feed per tooth. Even drills as small as .050” will still take a chip as thick as .001” per tooth.
For a quick reference on how fast to turn drills, consult fswizard.
Second – Cutting oil. It will lubricate the flutes of the drill so that the chips will move out of the hole.
Third – when drilling deep holes with a manual machine, it can be difficult to control the peck distance. Control the peck distance by moving the quill stop at every peck. The increments on the side of the stop are .001”, which is probably too fine for most drilling operations.
Last – Use a “sensitive drilling attachment.” It’s a drill chuck that spins with the spindle but will extend with hand pressure. This tool only allows you to control the peck distance if you use it at the end of its travel, which is unusual. Typically you just push lightly, feel it make a chip, and then retract the drill.