Hello folks.

I've recently had the situation to need to counterbore many holes in a 2000 mm (78'') part for screw heads. The through hole is ф6,5(1/4 '') and then we need to counterbore to 13 mm(0,51 ''). The depth was originally 5 mm but I later decided to give one more as screw heads weren't getting enough in so it became 6 mm(0,23 '').

The problem is that I cannot seem to find the proper cutting mode. I started much higher having some 3000 RPM and 220 mm/min (8,66 '' / min) because I truly don't have experience in this process. The sound and vibrations which resulted from the first trial were very noisy and I pulled things down.

By trials, I reached the following:
RPM = 1000
Feed = 30 mm/min (1,18 '' / min) which seems very slow to me. I mean, it is the only mode that the machine doesn't seem to have problems with. And for my great surprise, the RPM seems to be very important as well.

My co-worker was very little slower than the machine by doing the counterbores manually on a drilling machine with fixed Z coordinate.

My CNC is a self-made router with rigidity above the average. We designed it for extensive use with aluminium and so far it satisfies our ideas. The spindle power is 1.2 kW.

I would be interested in getting some raw data which has worked for you. I wasn't aware the counterboring process requires so much spindle power