Pull Stud Broke - Brother Spindle Trashed
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  1. #1
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    Default Pull Stud Broke - Brother Spindle Trashed

    We had a major crash on our fairly new (under a year old) Brother S500X1. The machine was doing a light facing operation with a Mitsubishi 2" 45 degree ASX 4 flute face mill - 10,000 rpm, .025 DOC, 150 IPM, on a 1.48" x 2.48" 6061 part. We had run about 10 parts on this run (300 plus with the same program and tools last month and over 12,000 over the last five years on at least 5 different machines - so not a new part), everything sounded fine, finish was great, and then BOOM! The machine made a bang and grinding noise for about a second before erroring out. Jogged the spindle up and noticed that the facemill was laying on top of the part with an insert stuck into the part (still clamped into the vise). I then noticed that the pull stud was broken at the base, looked for it in the machine and could not find it and did not until I looked into the spindle and noticed that it was still clamped into the spindle. The inside spindle was trashed at the spindle mouth and at the top of the taper where it spun on the tool.

    Called Yamazen to get service scheduled (this was Tuesday afternoon and they got a spindle shipped in and a service guy down and had it up by Thursday evening) so many kudos to them for prompt service. I then called Maritool support and told them that one of their 30 taper (not coolant through) studs (not more than 6 months old) failed and ate my spindle, tool holder, and facemill and that it looked like a possible problem with either material or heat treat process and they should trace the studs from our order and check any that they had. The response that I got was "they can break" and if I wanted to I could send the broken one back and they would inspect it. I have bought a lot of stuff from them over the years and have been happy but I am not now. Yamazen has gotten more aggressive on stud pricing so we are going to switch to their studs from now on - I don't like surprises.
    Attached Thumbnails Attached Thumbnails stud1.jpg   stud4.jpg   stud3.jpg   stud5.jpg   stud2.jpg  


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    Here are some more pictures.snap_003.jpgsnap_004.jpgsnap_002.jpgsnap_005.jpgsnap_006.jpgsnap_003.jpgsnap_004.jpgsnap_002.jpgsnap_005.jpgsnap_006.jpg


    There is no deformation at the break, just a clean snap.

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    Well it is true... They can break.

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    I saw the whole scene Thursday morning. Very cringe worthy. So the stud was the right shape and most probably the correct material. So either a material defect or improper hardening. Not sure what else it could be....

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    Quote Originally Posted by as9100d View Post
    Well it is true... They can break.
    That is not a "it wore out break", this is a bad heat or material break. We do somewhere between 5,000 and 10,000 tool changes a day across all the machines and have done so for at least 10 years and have never had a stud break. I replace them if they show any wear, but have not broken any. Our 40 taper machines run around 1500 pounds of retention force, the Brother with the standard spindle around 400. This is not a normal failure.

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    The shading in picture snap_002 looks to me like it had a pre-existing crack. The other pics are not clear enough to confirm that thought.

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    I agree with you and my comment was sarcasm. I would be furious as I'm sure you are.

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    It's very difficult to tell in the pictures but the grain structure at the break looks kind of large......maybe. A metallurgist or heat treat expert could likely tell with a quick glance in person. I could be wrong and say this cause in the past I have played around with heat treating and then breaking the samples to examine the grain structure. It is my understanding when you have the correct heat treat process the structure is very fine. IIRC quenching to quickly can cause a large grain structure. I also would guess the shadow is something with the lighting as I have never seen a crack propagate completely around the perimeter of a cylinder and then work its way in. Not that it couldn't happen but I don't think its likely.

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    Mickey_D,

    I spoke to you. I certainly did not just say ya they can break. I asked you about the application and I also mentioned they we sell high strength retention knobs that are much stronger and better suited for large face mills such as what you are using. A 2" cutter at 10,000 rpms is very fast. That application demands a high strength retention knob. Yes I offered to have my heat treater do an analysis. I stand behind all of my products.

    Not sure what else you want me to do? Send you a $10,000 check? It's very interesting how right away I am the guilty party. No possibility it was taking more than .025" deep. No of coarse not. Impossible. Part slipped out. Any chance 10,000 rpms is too fast for a 2" cutter. Any chance an insert broke off from centrifugal force?

    I just calculated 10,000 rpms on that cutter is 5,000 sfpm. Don't you think that would call for a high strength retention knob? I wouldn't call that a conservative application.

    Did you take advantage of our balancing service? That kind of mass at 10,000 rpms can really generate a lot of force. I have seen assemblies like this have a 50-80 gmm imbalance. This should be balanced as a whole assembly. Cheap insurance and will improve tool life and surface finish.
    Last edited by fmari --MariTool-; 11-06-2019 at 08:47 PM. Reason: spelling

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    The pics aren't good enough to judge the grain size, but I don't see any fatigue in the break- it just cut loose.

    That divot may have happened when it failed, or it could have already been there- a good look with a SEM would tell. Independent lab analysis might be worthwhile. Check the chemistry, heat treat, and microstructure.

    It looks like a heavy tool to push hard on a 30 taper, but if it's rated for 10K it should be able to run there. I don't understand that spacer/mounting arrangement- it seems kind of funky. If it's not integrated into the holder, it can't be good for the balance...

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    The only problem with 30 taper machines is they're not 40 taper, mostly with the way some are pushing them.
    We had one thread here a year or 2 ago where it 3-4 guys all had busted spindles around the same time due to pull studs breaking in their brothers, pretty sure they were various brands/manufacturers.

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    I'm intrigued by the depth of the divots from the retention balls, looking at photo #5. They seem much deeper than what I see on any of my many Brother BT30 pullstuds. Any chance your machine's drawbar is set too high, or there is something janky with how the drawbar meets up with the pullstuds? Do your other Brother pullstuds have deep divots like the ones in photo 5?

    Regards.

    Mike

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    Is this the first 30-taper machine that cutter/program has run on? I know this goes without saying, but is the uncut portion of the part the proper thickness for facing or did someone maybe get off a spin on the calipers??? I had excessive chatter pull a tool out of a dual-contact 30-taper but never brake a stud.

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    Quote Originally Posted by Finegrain View Post
    I'm intrigued by the depth of the divots from the retention balls, looking at photo #5.
    ^^^ Good catch Mike, I hadn't noticed that. It does look pretty sketchy.

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    The way those ball detents are so deep it really looks the the retention knob held on for dear life!! Some ball witness marks are perfectly normal. Those marks are very deep.

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    Don't know if this might take some of the sting out - but does your insurance policy have any coverage for stuff like this? I never considered it in the past, but my current provider put it in the policy for a very reasonable cost.
    Very sorry to see this.......

    I'll be taking a look at all my pull studs the next couple of days. Those divots do look interesting.

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    I am in no way taking sides and have been pleased with every Maritool product I own. I do find it interesting that it didn't fail at the smallest cross section. I was under the impression that tension failures occur across the smallest cross section?

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    Quote Originally Posted by Hardplates View Post
    I am in no way taking sides and have been pleased with every Maritool product I own. I do find it interesting that it didn't fail at the smallest cross section. I was under the impression that tension failures occur across the smallest cross section?
    Theoretically, yes! Especially in single-application ultimate failure testing....like just pulling until it breaks. This may have been more of a “fatigue failure” in which case there are several variables that can cause the part to fail differently than in single-application failure. Perhaps a rough transition in the area where the pull stud goes from being turned to ground (if it even IS ground?) That could act as a stress riser and be the weak link over several thousand or hundreds of thousands of cycles, even though it is not the smallest cross sectional area. I’m not implying that is what I think happened...it’s just an example of how a part does not necessarily always fail in the smallest cross section is all.

    Oh yeah, the crack can propagate from the OD towards the core if the failure is from cyclical *rotational* forces, which would be a reasonable consideration given the machine’s knack for applying cyclical rotational forces. Given how close most of the shadow is to the OD I would bet a Coke that it happened pretty quickly (i.e. “high stress”)

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    So how'd the divots get so big? If it just let go, you'd think they'd be normal size as the defect was below. If they whole thing was soft, that could explain it.

    Yes, insurance can cover this. It covered replacing my first spindle which was 100% programmer/operator error.
    Last edited by CosmosK; 11-07-2019 at 04:14 PM.

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    Quote Originally Posted by Nerdlinger View Post
    Is this the first 30-taper machine that cutter/program has run on? I know this goes without saying, but is the uncut portion of the part the proper thickness for facing or did someone maybe get off a spin on the calipers??? I had excessive chatter pull a tool out of a dual-contact 30-taper but never brake a stud.
    This was the third batch of about 400 of these parts that had run on this machine and we had run about 10 pieces in this run when this happened. Part was still in the fixture but pried up a little where the insert had dug into it and the fixture. That little Mitsubishi facemill is (or was) rated to either 16 or 18,000 rpm (I am at home now and can't look at it) and we run them in our Okuma 560s at 12,000 and 14,000 rpm regularly and they give an incredible finish. They even give a good finish in our tired Hardinge GX480 with 8,000 plus hours on it. As for the line that looks like a crack on the stud, it is oil/coolant residue from when it ejected from the spindle when I swapped it into an empty tool pot.


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