On Sun, 22 Apr 2012 20:20:11 -0700, "Bob La Londe"
wrote:

wrote in message
.. .
To all you folks who are actually making parts from metal,
I use form taps, AKA roll taps, as much as possible. I use them for
not just the easy to tap materials such as 6061 and mild steel. 304
SS, 17-4 SS, 4340 and 4140 steel are metals I have had good luck with.
Die cast aluminum alloys too, though I don't know what specific
alloys. I have also tapped sand cast aluminum parts but only a few
times and I don't know how well the threads held up. But now I'm doing
a lot more sand cast aluminum parts that are various alloys, 356 being
one of them. I would like to form tap all the cast parts and I'm
looking for advice from anyone here who hasreal world experience with
sand cast aluminum parts that have had form tapped holes. I want to
give the customer the best threads and even though formed threads are
usually better I know that sometimes the formed material can become
brittle from the forming operation leading to weaker threads. I have
contacted a couple tap makers with this question but they have not
given me any information beyond saying that I need to determine what's
best.
Thanks,
Eric


Makes some parts, tap them with a couple different processes and clearances,
then put a bolt in them and twist with a torque wrench to see when the
threads strip. Use the best compromise between machinability and real world
strength requirements.


I think that's a great idea. I'll ask the customer today for some of
the pieces cut from the castings and test them.
Thanks,
Eric