In article , "K Ludger" wrote:
I've got a job coming up to drill around 300 x 25mm diameter holes in some
powder coated steel electrical enclosures. The metal is 1mm thick, probably
30 - 35 thou. Punching is out, I need to do this using my drill press.

I've done a bunch of holes in the past using a step drill, and then spent
almost as much time again deburring the holes. I'de very much like to avoid
using coolant or Trefolex due to the cleanup involved with the enclosures.

I'd like to drill the holes in one go (ie not pilot then change & drill) any
recommendations as to the best approach or tool that I should use?

The ideal thing for sheet metal is something that can remove a disk,
rather than having to chew out all or the material. I've never used a
RotaBroach, but if you can afford one, that may be your best bet. I'm
not sure how bad they are for burrs. If you don't like deburring, a hole
saw will probably be worse than a step drill. A trepanning tool might
also work if you can hold & support it well.

Actually, I'm surprised you have a problem with burrs with the step
drill. A good quality one (not a Chinese knock-off) has always cut a
pretty clean hole for me, and if you move up towards the next step, you
can deburr the top side in the same operation. For the backside, I use
soemthing like a Noga or a Royal with the "?" shaped blade to get the far
side of the hole.

With any approach, having a good hard backing surface will help with
burrs and safety. If the metal can flex, it can grab, expecially if you
you a single point adjustable cutter. A trepanning tool tends to scrape
more than dig in, so it's a bit safer.

Doug White