I've used an M4 drap on nominally 3/16" tk. Al and don't ever remember breaking one. I did it to save on tool holders--what's your excuse? I spot drilled with an engraving point but a center drill or real spot drill would work also. I wasn't concerned about location as much as a burr-free, countersunk top surface. I drilled through the part at high rpms, then called a G84 which was ridgid tapping mode. This was a very slow operation since the spindle was always changing speeds or direction. You have to use a drap in a hand fed drill press and a tapping head or in a CNC machine with ridgid tapping! A floating tap holder is not going to be ridgid enough for drilling in a CNC and you can't use a ridgid collet or tap holder in a CNC without ridgid tapping. |