Thread: Counter Sink Bits,

From my experience of production laser cut steel parts, I suspect that you may be up the creek.

There are two issues that I see causing problems.

1. The laser cut holes are extremely unlikely to be round or have a decent smooth wall, particularly in 5mm dia. The cutting process uses a huge amount of heat from a finely focused light beam to melt the metal in the arranged pattern, but the metal has to flow out through the kerf before solidifying again. More often than not, it doesn't, leaving a joining segment holding the core in place. Even if the hole is fully cut and the centre is cleared and removed, the walls won't be parallel as the process normally produces undercut.
2. The local heating in the cutting process will significantly harden the metal around the hole making countersinking with a decent countersink difficult. We used to run 8mm holes in 10mm plates, often had to tap the cores out with a hammer and punch and clear the holes with a cobalt drill. To countersink, we used a bastardised 13mm cobalt drill (short about 10-15mm of flute left) sharpened to the correct angle. While we had a good selection of zero flute countersink bits available, only one newcomer ever used them on laser cut holes, stuffed three bits on a single hole, a very expensive lesson. The bastardised drill at least was resharpenable.

For your job, I suspect that you would be better off settting out traditionally and drilling and c/s with a decent drill press, sharp drill and a zero flute c/s bit. If you need to do a lot of these, then a fence and stop setup would be suitable for production quantities.

Piloted counterbores are available, but these make flat bottom holes. I've never seen a piloted countersink, maybe because they aren't considered necessary as they are self-centering to some extent? A tool & cutter grinder could make any type of specialised drill or counterbore I think, if you could access one.
Jordan