Dull drill bits - throw them out

[travis]

In thin gauge Al, I start every hole with a #40. This is not only the smallest practical bit in my opinion, it is also the hole size for a 3/32 rivet (and the associated cleco clamp).

The middle of your standard 118° chisel point twist drill does not so much cut, as mush metal out of the way. The chisel point is also the first part of the bit to dull. The only bit that has to do difficult center cutting is the pilot, so you might as well use a small one to limit the force required. After that you can generally chase the hole with your desired drill. If you are drilling a particularly big hole, measure the web thickness of your finish bit, and select an intermediate bit that is larger. This wil ensure that only the best cutting geometry of your bit is put into service. This can be a little chattery with a hand drill, but takes less dangerous effort.

Drill sets are a waste of money and space (I bet you use that M bit 50 times a day). If you design your own robot, you can keep fastener type count down, and only need a few bit sizes.

My bit of choice for hand drilling Al is jobber's length, 135° split point, HSS, bright finish. HSS is less brittle than cobalt and plenty hard and heat resistant for Al. Bright finish (no coating, just polished) is fine at preventing chip welding in Al, much better than any import-grade coating. The split point helps with wandering, but if you start with a #40, you almost don't even need to center punch. That configuration is also about the cheapest there is, so buy from a nice name brand made in USA/Switzerland company and get a zillion #40s. Good tooling doesn't cost money, it makes money (and prevents doctor visits).

If you are still breaking bits, get a faster drill, like a <=3/8 chuck air drill, which is also lighter and easier to control. The recommended RPM for drilling an 1/8" hole in Al is about 12KRPM, or around 5 times faster than your average battery powered drill. Screw length bits are about half as long as jobbers, and thus less likely to snap in twain.

travis "drillbit" taylor