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On Tue, 24 Apr 2012 10:01:09 -0700, "Bob La Londe"
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On Mon, 23 Apr 2012 16:57:13 -0700, "Bob La Londe"
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news On Sun, 22 Apr 2012 22:18:09 -0700, "anorton"
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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

If thread strength and durability in aluminum is really an important
issue,
you might want to ask your customer to modify the design to use
helicoils.
Many of the castings I machine do get thread inserts. In fact, that's
part of the reason I got some of the jobs. I convinced the customer
that I could install the hundreds of heli-coils faster and cheaper
than they were doing them.


*** I use a tapping head to install them. ***

Now that is something to remember. I could make an insert tool to
install
them out of drill stock pretty darn quick too.




I use a Procunier head because it does not self feed. The install
depth of the inserts varies less than .005"


I just have a cheap no name tapping head, and the self feed does cause me
headaches sometimes. I just can't afford a Procunier head. Still, if I
take the time to do a setup properly and set my drill stop with some
experimentation I can eliminate most of my troubles. Not convenient for
one
or two holes, but worth it when I have to do 20-30. I read your comment
and
thought... a reason to buy another tapping head and another drill press.
LOL.

If you try it you'll like it. I have bought all my Procuniers on ebay.
Except the first one I bought. I got that one at a flea market. It was
in pieces in a coffee can. The cork lining for the clutch had come off
of the aluminum hub. I epoxied it back on and it has worked fine for
the last 25 years or so. And the tapping head itself was made before
WW2. I never paid more than 60 bucks for one by the way.
Eric

You know, my dad has an electronic variable speed reversible drill press he
bought from Sears atleast 35 years ago. I've often thought if I had that I
could make a simple spring centering lockup tapping head without all those
fancy internal gears. I always thought it was "cheap" and light duty, but
when I asked he sais the only thing he ever had to do to it was replace the
speed control pot when I broke off the shaft as a kid.