On Fri, 09 Jan 2009 15:54:38 GMT, Norm Dresner wrote:

I confess that it's been 50 years since I took shop classes in college and
while I've done some things regularly since then both professionally and as
part of my hobby work, I've had very limited experience in certain areas.
SO ...

I've got a bar of aluminum that I had to drill and tap several 1/4-20 holes
in. The bar is roughly 7"x1"x1.25" and drilling and tapping the holes
through the thickness (1") was a good refresher course, but the hole through
the height (1.25") has me stumped. Without thinking it through, I drilled
the hole and started tapping. But the tap's cutting length is only 1" and
the shaft behind it is too thick to pass though previously tapped metal.


Do you need the whole length of the hole threaded?

If not, drill a clearance hole for the tap and keep going.

If you do, you could grind the shank of the tap for the extra quarter inch;
a cheap carbon tap in aluminium should be ok, especially if you have a good
sized tap hole and some wd-40 with which to lube the tap.

I presume you don't have a lathe - single-pointing with a boring-bar works.