G’day; difficult, but well worth a try if you have the right taps and
tapping drills. Right then, we will assume that since you are making
’blind’ holes, you will have a taper, medium, and full (bottoming) tap
of the right size and thread. The first and third are essential but
the medium is a great help. Whilst a lathe and Slocum Centre bit are
the best way to go, it can still be done without. Firstly make a
conical hole in a suitable piece of wood, plastic, whatever, using a
countersinking bit (as for screw heads) Place the ball in this and
using a fine centrepunch, make an indentation in the judged centre of
the ball. To hold the ball in place whilst drilling, make a hole in a
bit of transparent lucite or perspex a little smaller than the ball,
and use it to clamp the ball in place. Now, with a drill press holding
the tapping drill (leave only about 1.5 cms of the drill showing to
provide less chance of the drill breaking) well lubricated (I am El
Cheepo, and find my spit works fine and is always readily available)
Drill with light pressure, and lift often to clear the swarf. If the
threading tap is a small one, DON’T use the usual tee type tap wrench.
After starting the tap true by turning the drill press BY HAND, take
the tap out and put it in a pin vice, tighten well, then complete the
threading with very frequent backing off and lubrication. Be aware of
increased restriction against turning the tap; taps aren’t all that
expensive, but there is no need to see how easy it is to break them.
Repeat this with the medium, and then the bottoming tap. After
removing the last tap, get yourself a beer or a sherry, gin and tonic,
or whatever as reward for a difficult job well done. Warning:
don’t attempt to do this with a hardened STEEL ball bearing: it won’t
work unless you anneal it first. The ‘ball clamp/holder’ will work
well for drilling pearls too. It can all be done without a drill
press, but even more skill is needed. Cheers and happy tap
dancing,-- John Burgess; @John_Burgess2 of Mapua Nelson NZ