I've had 2 break.. One was many many many many moons ago.. It was on a tool holder
that came with the machine, and we just used it.. And then all of a sudden it wouldn't come
out of the spindle. Had to push the button, and it took 2 guys on 2 pry bars to get her out.
The culprit.. OVER TORQUEING!!!
What broke??? The flange.. And when the flange disintegrated, the stud didn't have
any tension in it, and it got a lot shorter.. I really wish at the time I had put that sucker
up on a granite plate and measured how much shorter it was than it was supposed
to be...
Solution, we pulled all of our studs, and had them mag particled, 140 or so tool holders.
Not a single crack found in any of the other studs.
My second failure was just a few years ago.. 3/4" holder, with a really long 3/4" ball
mill in it.. It was on a Fadal VMC15, so it was just piddling along doing something
stupid, I might have just been piloting for a .754 reamer or something. The tool
came back up to the tool change position, and the tool holder fell out, without the
end of the pull stud attached..
First, I must say, that I do have some cheap shitty e-bay pull studs kicking around, I
REALLY thought I had them in only ER16 holders, holders that aren't going to get
worked hard.. I was WRONG!!!!!!!
It was a cheap shitty e-bay pull stud from years ago. It was cracked, it had been
cracked, you could tell by a little bit of rust and some discoloration, it was hanging on
by maybe a square millimeter of real metal.. I think I still have the threaded section
floating around, if I can find it, I'll post a pic.
I consider myself one lucky bastard that that pull stud let go when it did. I ate up a
lot of karma that day.
My pull stud thoughts.. DO NOT BUY CRAP!!! and if you do buy crap, put it on
tool holders that don't get a lot of stress. Small drills, little endmills, those kinds
of holders..
If you are nervous, have them mag particled.. Quality pull studs aren't free, I'm
pretty sure getting them mag particled is cheaper than buying new. If you are that
nervous, buy new ones.... GOOD ONES!!!!! not from E-bay.
And last, but not least. Install and torque them properly. Tighten until it starts to
loosen and then back off a quarter turn does NOT work for pullstuds. I don't even
think you need a fancy pull stud installing torque wrench, any machinist(mechanic) worth a
nickel can gauge it pretty good, and again, if you are nervous, double check your
feel with an actual torque wrench.. If you don't trust yourself to get it close by feel,
then buy the fancy adaptor, I'm not saying that there is anything wrong with that, because
there isn't. If I ever get a quarter million dollar machine, I'm buying the fancy adaptor.
Also look up the proper torque specs, its a LOT less than you think it should be.