ATM Re: How to make accurate holes with hand drill?

[Bill Abbay <b.abbay@humboldt1.com>]

This is a bit of slant on the original question but it might be of use
to some.

When assembling aluminum parts together using screws, some sort of
fairly precision alignment is needed between the pieces while holes are
being drilled and tapped.  It may not always be practical to clamp
things. As an example, let's use a popular Crayford focusser design
which uses a short piece of 1/4" aluminum angle "bearing carrier" that
is attached to a base plate by screws from beneath.  What I do, after
throughly cleaning all the parts, is simply 5-minute epoxy the two
together, being sure they are set accurately to their desired position. 
When set (I allow 30 min.), carefully locate and drill the tap holes all
the way through the base into the angle.  Next, drill the screw body
hole just through the base, then tap the holes that you've drilled into
the angle.  The body hole helps tremendously in keeping the tap
accurately aligned.  When all done, take a butane torch and carefully
heat the parts till the epoxy melts.  It needs a fair amount of heat but
nothing like what will harm your work.  Let the parts cool, clean of
residual epoxy with a dull razor blade and you're done.  The parts will
now reassemble perfectly and small variations of hole position won't
matter.

Bill Abbay