Minor problem to solve 

I didn't ever expect to be able to contribute anything mechanical to this channel, but here's a try: - There are spot face drills with a replaceable guide tip. Imagine taking a hole saw and replacing the guide drill with a smooth rod. The set I had BITD was matched to Allen head screws. So first you drilled for the major diameter of the thread, then you picked the appropriate spot face drill and used the guide tip to center up on the hole.Then you drilled for the flat bottom hole and you'd be done. Naturally, I soon found a reason to extend the use of this very special set, so I made new guide tips which allowed me to use the drills in off size combinations. This allowed me to ues this set originally intended specifically for Allen heads to trill clearance holes for hex heads and sockets etc. Making new guide tips was an easy lathe operation, and you're pretty much free to pick your own tolerances. Unless you're doing a production run, getting it good enough wasn't much of a problerm.

I've had the odd misfire thx to those little doohickeys working loose..

All hail the Algorithm!

If you are anywhere near Monmouthshire, I could whack it on my CNC and helical interpolate the spot face 😇