How to remove side effect caused by drilling holes on aluminum?

[Snoopy]

Hello, after drilling holes on aluminum plate, I found that the other side of the plate became unflat because there are new circular edges developed on the other side of the plate. How can we prevent this problem from happening? How do we remove those newly developed circular edges to make both sides of the plate flat? When I was drilling holes, I put wood/metal underneath the aluminum plate. This did not stop the issue from happening. Thanks.

[jwatte]

Hello, after drilling holes on aluminum plate, I found that the other side of the plate became unflat because there are new circular edges developed on the other side of the plate. How can we prevent this problem from happening?

First, this is a machining question. I've found "practical machinist" and "cnczone" to be good forums with lots of machinists helping out.

Also, doing metal working on a wood drill press is not a good way of getting high precision. If at all possible, find a knee mill, or even a small CNC mill (not router) of some sort.

To answer your question: You use sharp cutters (drill bits in this case) intended for the job (no Home Depot Chinese wood drills coated with golden fairy dust.)
Typically, you'll want a wider tip angle (> 130 degrees) or even a center cutting end mill.
You also must plunge slowly -- let the drill cut the metal without poking into it too much.

In the end, you may still get exit burrs on the other side; those should be removed through regular de-burring methods (anything from a hand file to a vee bit from the back to a sand shaker.)

If you're using metal plates to help, you need a very flat piece of metal, with heavy clamping forces, to keep the sheet flat. Ideally, you create a jig out of stainless steel with the exact holes you need, at which point you can push as fast/hard as you want (without breaking bits) because it will work like a punch if you go too fast :-)
You need the jig to have both a top and a bottom bit, and as I said, it needs to be very flat (as in: machined.)

[tician]

Basically, the aluminum is too soft and the drill bit too dull. As the center of the bit pushes through the back side, the thin bits of aluminum around the circumference deform instead of getting cut by the bit. Not much you can do other than use a deburr tool to remove them during a finishing stage after drilling everything.

6061 and 6063 aluminums tend to drill very cleanly because of their relatively high stiffness, but they do not usually bend safely without heat treatment. 5052 aluminum is a bit softer so tends to produce more burrs, but it can be reliably bent at room temperature without breaking.

[Peter_heim]

There are ways to grind the drill bit for soft metal but unless you are good with sharpening drill not try just use as flat a drill bit as you have
in the photo you are using to much pressure and drill to blunt. My day job is aircraft engineer I drill lots of holes in alloy a nice fast air drill sharp bit with the job clamped to a flat surface (wood) is all you need when the drill starts to break through back off the pressure and let the drill bit do the work the wood on the back is to stop the drill from pulling through on the flutes. If you dont get 2 nice swarfw tails when you drill you bit is to blunt

peter