On Sun, 11 Oct 2009 14:04:36 -0500, John Fields
wrote:

On Sat, 10 Oct 2009 22:58:26 -0700, Archimedes' Lever
wrote:

On Sat, 10 Oct 2009 10:11:16 -0700, Jim Thompson
wrote:

1/4"-20 tap calls for 0.201" tap drill (13/64")

Into a steel 1/8" panel, tap is hard enough to turn that handles flex
:-(

Is that normal, or do I need to go up one or more drill sizes?

...Jim Thompson

1/4 - 20 through a mere 1/8 hole is too coarse a thread for that little
thickness. Use a #10 or a metric.

Also, tapping a hole has a bit of art to it. If you do not know the
limits of the metals the handles and taps, etc. are made of, you will not
know the tricks of performing the task, like the one where you only turn
a 1/4 turn or so at a time, and then back off and then go back in, and
you slowly work the tap, not attempt to make the turns all in one fell
swoop, and yes, some sort of lube is needed.

If you insist on the 1/4 - 20, then you can use the edges of the drill
to open up the hole a little bit. Makes the tapped hole a bit looser as
well, however.

Ideally, a panel that thin for a hole and subsequent bolt that size
should get a boss welded onto the back side of the hole so that the
number of threads is increased You should tap the boss first as it will
harden up when welded, and then you chase the tap back down through the
hole again after it has cooled.

---
These work fine without welding:

http://www.pemnet.com/fastening_products/pdf/cldata.pdf

Drill, press, done!

JF

Well, a drill press, and usually a special press block to swage the
union together.

But yes, I mentioned PEMs in this thread elsewhere. They are great,
and the most common current solution employed.

Above a certain size though, you will still see welded bolsterings for
holes. You can remove the temper by re-heating it with a torch after the
weldment is done and letting it cool slowly.