[daleman]

we recently bought a brand new vf2 with the gearbox option my question is has anybody ever had a pull stud break whilst the machine is in motion .
We were spot drilling a hole when there was a noise no machine alarm and the machine kept on going.
But without the tool in the spindle the tool had been ejected mid cycle whilst spot drilling and haas are now claiming it must have been a faulty pull stud.
now I've been using cnc machining centers for the best part of 20yrs and have never know a pull stud to fail ever .
has anybody known of one failing in this way ????

[Machineit]

Yep, bad pull stud. They should never break in the machine. If you bought a bunch of them, I would get rid of the rest and replace them.

Mike

[daleman]

the pull stud was at least 12 months old and I've never seen one break when just spot drilling

[Machineit]

the pull stud was at least 12 months old and I've never seen one break when just spot drilling

Well, now you have!

Up to you, but you were not putting any side pressure on the tool which would tend to try and pull it out of the spindle, only pressure back into the spindle from drilling.

So, you can choose to decide it must be a defective machine which puts enough pressure on the stud to pull a nearly .400" diameter hardened stud apart, yet is still able to do normal tool changes, or you could assume that it is the stud itself that was damaged or defective.

If you decide it is the machine, I guess you could pull the spindle off and remove a few of the Belleville washers to reduce the pressure, or if you give up on the VF-2 you could give it to me and I'll arrange the shipping. On second thought, not from the United Kingdom. On third thought, it is a new machine, maybe I can invest the money to ship it across the pond!

Good Luck----Mike :wave:

[haastec]

we recently bought a brand new vf2 with the gearbox option my question is has anybody ever had a pull stud break whilst the machine is in motion .
We were spot drilling a hole when there was a noise no machine alarm and the machine kept on going.
But without the tool in the spindle the tool had been ejected mid cycle whilst spot drilling and haas are now claiming it must have been a faulty pull stud.
now I've been using cnc machining centers for the best part of 20yrs and have never know a pull stud to fail ever .
has anybody known of one failing in this way ????

I will agree that this is extremely rare, but I do believe that it was probably a bad pull stud.

If you are still worried about the machine having a problem, find someone to test the drawbar with a drawbar force guage.

Good luck!

[Geof]

I think 'probably' can be upgraded to 'the only logical conclusion is a bac pull stud'. The drawbar tension is a bit less than 2000 lbs and the force needed to break a pull stud is many times this, the machine simply could not exert enough force to snap a pull stud in good condition. Which introduces a question: was it a new pull stud? If the answer is yes then I would suspect it had a crack from the heat treatment, if the answer is no I suspect it had developed a fatigue crack. Either way you should be able to see evidence for this on the broken surface.

[Ydna]

I've seen the results from fatigued pullstuds before. Never been there when it actually happened, but seen the tools and workpieces afterwards. Or should I say what was left of tools and workpieces. Granted, it was never during a drilling operation...but hey weird stuff happens.

We replace all our pullstuds about every 2-3 years or so. I inventory them when purchased to keep track of it. (the manuf is nice enough to already engrave serial numbers).
Some people have suggested swapping them more often but it's likely not necessary unless you're performing heavy duty cycles continuously.

It might be a bit overzealous but I don't personally have *that* many holders so I'm fine with it after running the numbers. I'm not the type of person that is likely to go for an "insurance" route, but I'm okay with loosing a couple hundred moneydollars in pullstuds for some extra protection against annihilating a spindle bore.