Center Drill Drill Depth

[bowersjack]

Does anyone know of a chart or formula to help me find drill depth for KEO combined drills and countersinks to give me a finish countersunk hole in my programming? Or do you use spotting drill instead? Thanks Jack

[Geof]

Originally Posted by bowersjack Does anyone know of a chart or formula to help me find drill depth for KEO combined drills and countersinks to give me a finish countersunk hole in my programming? Or do you use spotting drill instead? Thanks Jack

They call them 'combined drills and countersinks' but they have a 60 degree taper on the 'countersink' part which is not correct for a flat head countersunk screw. Right now I can't remember exactly, but the angle for a countersink is 87 or 89 degrees so even a spotting drill at 90 degrees is not exactly correct. I have been told it is possible to get spotting drills with the correct angle but have never seen them; for non-critical work the 90 dgrees is often okay. Using a spotting drill also gives the advantage that you can spot for the hole location to stop the drill wandering on entry, and go deep enough to leave the countersink at this step; saves a bit of time on multiple holes.

[mixdenny]

Originally Posted by Geof They call them 'combined drills and countersinks' but they have a 60 degree taper on the 'countersink' part which is not correct for a flat head countersunk screw. Right now I can't remember exactly, but the angle for a countersink is 87 or 89 degrees so even a spotting drill at 90 degrees is not exactly correct.

The SAE standard is 82 degrees. Aircraft standard (thin panels) is 100 degree, although you don't come across these very often. Metric flatheads are 90 degrees. I have lots of 82 degree countersinks, but only a few 90 degree for the occasional metric job.

Dennis

[Geof]

Originally Posted by mixdenny The SAE standard is 82 degrees.....Dennis

Thanks, I try reciting that to myself a few times .

[cnc-king]

Originally Posted by bowersjack Does anyone know of a chart or formula to help me find drill depth for KEO combined drills and countersinks to give me a finish countersunk hole in my programming? Or do you use spotting drill instead? Thanks Jack

may be this will help. this is a table i created when i first started in the trade before the days of excel