On 2012-02-09, DougC wrote:
On 2/9/2012 12:06 AM, DougC wrote:
........
I had assumed there would be taps & dies for this. I have found many
sources for cheap dies (pipe threading kits) but no taps yet, and the
dies are "long" because they are for threading pipe.... Is there any
'normal' taps & dies sold for this, at a /relatively/ cheap price? I
just need the one 3/8"-18 size, internal & external.


Well really, it looks like it is easiest & fastest to just order a
T-fitting and nipples already made off of McMaster,,, but I am still
curious.

The methods that I have seen for cutting tapers (or tapered threads) on
a normal lathe is to offset the tailstock, and spin the part between
centers... but you can't do that if you're cutting internal threads.

Yes, you can't.

And doing an external tapered thread without a taper attachment
can also be tricky, depending on the length of the pipe to receive the
tapered thread. If it is too long, you can't mount it between centers.
And you may not be able to get enough offset in the tailstock to get the
right taper, either. (BTW, turning between balls might be easier than
between centers for pipe. Make up centers which end in hardened balls.

So that is why I am wondering how to cut internal tapered threads on a
manual lathe without a taper attachment, or if it can even be done.

Yes -- with a tap made for the thread in question. They are
made and sold. I have some of various (small) sizes.

There are also matching dies.

And there are chasers for Geometric die heads to cut tapered
threads as well as straight ones, if you happen to have a bed turret for
the lathe.

Enjoy,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---