Thread: Pull Stud Broke - Brother Spindle Trashed

looks like a simple case of using a 30 taper to do a 40 taper job . It sounds like you got away easy with only a screwed up spindle ...

I have seen other posts about brother pull studs busting and even the shop I went and looked at a twin pallet brothers at the guy told me they had busted a pull stud and had to replace the spindle ... from what I have seen the 30 taper machines were originally built to be drill / tap centers and over time have been "PUSHED" into being milling machines ... Drill / Tap puts the load inline with the spindle and has vary little side load ,,, milling on the other hand puts most of the load perpendicular to the spindle. I think someone needs to rethink the loads the small 30 taper pull stud is seeing ...

Originally Posted by fmari --MariTool-

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.

That is the only stud that has marks like that and they probably came from being flung around inside the retainer. The other ones that we got from Maritool and Yamazen all look virtually new.

Is this a bash maritool thread, or a cautionary thread about pushing a machine to its limits?

Manufacturing is not a perfect science. Too many factors. The pull stud could have been defective. But I have used many items from maritool with great success.

I also have 2 brothers on the shop floor now and have broken pull studs on both (only one spindle replacement) from pushing my luck. Just want to make sure we take the right message away from this.

Originally Posted by Nerdlinger

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”)

I would be very surprised if this tool on this Brother machine had seen more than 2000 cycles. We primarily use the Brother for a family of parts that get 3rd op side holes in them. These parts with 4 or 5 tool changes on the Brother will run for about 20 to 25 seconds vs. 3 or 4 times longer on the big Okumas. Now the Okumas kick the Brothers butts in material removal and finish quality, each machine has a place in life.

Originally Posted by fmari --MariTool-

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.

When I called Maritool before ordering about $1500 worth of ER-20 and ER-32 holders, pulls studs and a face mill holder I asked the person about what studs were needed and was told that the standard non-coolant through studs would be fine on the regular and not high torque spindle. That is whey I ordered them.

Originally Posted by Mickey_D

I would be very surprised if this tool on this Brother machine had seen more than 2000 cycles. We primarily use the Brother for a family of parts that get 3rd op side holes in them. These parts with 4 or 5 tool changes on the Brother will run for about 20 to 25 seconds vs. 3 or 4 times longer on the big Okumas. Now the Okumas kick the Brothers butts in material removal and finish quality, each machine has a place in life.

I *think* every time an insert in the face mill is entering and leaving the cut that cyclical loading/unloading can get transferred up to the stud. Do not just the cycles from tool changes...I *think*!

Originally Posted by Nerdlinger

I *think* every time an insert in the face mill is entering and leaving the cut that cyclical loading/unloading can get transferred up to the stud. Do not just the cycles from tool changes...I *think*!

Don't the drive lugs take up most of the torque about the z axis?

Originally Posted by mneuro

Is this a bash maritool thread, or a cautionary thread about pushing a machine to its limits?

Manufacturing is not a perfect science. Too many factors. The pull stud could have been defective. But I have used many items from maritool with great success.

I also have 2 brothers on the shop floor now and have broken pull studs on both (only one spindle replacement) from pushing my luck. Just want to make sure we take the right message away from this.

I am not trying to bash Maritool, I have used their stuff for years and have been happy with it, but I am sharing my experience about a pull stud failure. This pull stud suffered a very quick brittle failure. No elongation, deformation, or give at all, it just snapped. I am going to dig in my junk drawer and pull out some old long and skinny Haas style through coolant studs from my Hardinge, put them in a vise and whack them with a hammer and see if they snap like these did or give a little before they fail. Some probably have over a hundred thousand cycles on them.

Originally Posted by Mickey_D

Part was still in the fixture but pried up a little where the insert had dug into it and the fixture.

So did the part lift cause the crash or did the crash cause the part lift?

BT30 pull studs breaking is not unheard of, but neither is improperly tightened workholding.

You might call T.J. Davies about pull studs ,,, I think that is the only thing they make and have been around for a long time...

Its sounding like the pull stud is just to small for the machine .. I have seen busted studs on 40 and even 50 taper machines but "EVERY" time is was from a CRASH ... Brothers seems to bust the studs and cause the crash ...

Originally Posted by Radar987

So did the part lift cause the crash or did the crash cause the part lift?

BT30 pull studs breaking is not unheard of, but neither is improperly tightened workholding.

The part was still in the fixture but one side (the side with the carbide insert and seat stuck in it) appeared to have been pried up by the crash. The tool was still partially in the spindle when the machine tripped out. We have worn out several of the fixtures over the years (make them out of CRS 1018) and when they wear parts get flung out. The worst that we have had from that are a few chipped inserts and chipped paint inside the machines.

Yikes,
Sounds like I need to slow the fk down. I'm new to this, and I've been running a 2" ripper mill .2" deep 1.8 step over at 120 ipm since I got my s500 in January. Spindle load meter is at 50% of scale (all green). I leave .02 for a finish pass and I can see my nose hairs in the finish. Having only used a hobby mill before the brother, the spindle would stall and fault before breaking a tool holder. Still a lot of learning to do.

It might be worth getting some hardness testing done on the pull stud remains at the cylinder and crack face, as well as on the ball seating cone. I do find it odd how dented the cone is, as well as dent placement, it's as if there was a force pulling the facemill and holder out of the spindle, drawing the cone through the drawbar such that the balls dug in.

If that's the case, something put an extra downward axial force on the toolholder, perhaps through engaging the workpiece due to poor seating or clamping in the vise, but that's just a guess. It would be worth examining the drawbar retention end to see if the ball socket holes have been dimpled or elongated from extra tension.

We don't see many signs of fatigue in the cracked area, it does look mostly like a pure tension failure. I'm thinking that the small dent in the bottom left of pic #3 in the second post is from impact after separation, but matching the two stud pieces and looking for a "dent mate" in the cylinder would clear that up - it wouldn't be present in the cylinder if due to impact after breakage.

This sucks for all parties, hope Mickey has business insurance that will cover the cost.

Here's a short article on the importance of the lowly pull stud: Pull studs: under pressure | Blog | Resources

And here's another thread on a 30-taper stud break: I killed my spindle...

Pay particular attention to post #20...

Originally Posted by Finegrain

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

...and check all your other holders ASAP incase there's any other pullstuds with this deformation in the 45degree face...

Ref these *little machines* and my experience FWIW...

I originally had 2x Robodrills (E models) 1x with BBT spindle, 1x standard spindle.
Talking ally here - A 40mm (3 tipped) dia Korloy facemill i'd run at 10k rpm, 2.5mm DOC and a feed of F5000. It was sweet.
A 16mm dia MA Ford (45deg knuckle rougher) would run (in a Maritol stubby sidelock) at 10k rpm, 20mm DOC, 30% stepover and a feed of F5000 on the BBT.
On the standard spindle, i dropped it to F3500 because it sounded too noisy.

Replaced the machines with 3x Feelers all #30 taper and BBT spindles.
The 16mm sounded better (more solid) but we swapped everything out so a 14mm dia was doing the hogging.
Machine was shed loads quieter - smaller circumference so there were always 2x teeth incut with the material - unlike the 16mm diameter where it was one tooth followed by the next tooth etc so was always vibrating "hammering".
Sound is vibration - if it doesn't sound *sweet* don't do it because they're baby machines which are awesome fast at metal removal, but the weak link is and always will be the pull stud.

Originally Posted by Hardplates

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.

I was thinking exactly the same. Grains look lot larger than what I'd like to see.

Doctors have a saying - when you hear hooves, go look for horses and not zebras.

On one end of the drive train, you have a broken pull stud, but on the other end of the equation, you have evidence that the workholding failed. You are also running a 2" face mill at a very high RPM - a hairy prospect that requires maximum process reliability in a BT30 machine because the risks of failure are extremely high.

I've seen lots of postmortems on Speedio/Robodrill spindle blow-ups. Not a single one has ever been attributed to outright pull stud failure. The most common one is workholding failure, followed closely by tool clearance plane issues leading to G00 collisions.

Personally? The only face milling I'll do on a BT30 machine is with a Sandvik Century with PCD inserts because I want the luscious surface quality. Literally a .005" DOC, at 16k RPM and a starting feed rate of 100ipm that I'll bump up to 200IPM after the process/workholding is very well proven. I've retired the 3" Century for a 2" and 1.5".

If I need to deck off a lot of material, my goto is a 1.5" Shear Hog mini modular head in a BBT30 Maritool screw-on holder with a Maritool high strength stud. The Shear Hog is very old-school and designed for taking big, chunky chips out on low speed machines. Using adaptive paths, maximum RPMs and moderate feeds per tooth, you get really solid MMRs while keeping the process reliability very high. The small diameter and adaptive paths means workholding failure has a lower chance of binding up under the tool and leading to stress on the spindle.

TL;DR- I think it is way too early in the diagnosis here to be throwing Frank/Maritool under the bus. Especially when a company with a sterling reputation for going above and beyond to stand behind their products has offered to do a complete inspection of the failed component. Perhaps let them do that and have an opportunity to help before jumping to conclusions?

A lot of interesting conversation going on with this, I am sorry for the damage but glad you decided to share. Frank is offering to have the stud checked by a professional, it would be interesting to see what that person has to say about it. I hope you decide to let him have a look at it and if you allow it, please share the findings here.

Charles

Originally Posted by CBlair

A lot of interesting conversation going on with this, I am sorry for the damage but glad you decided to share. Frank is offering to have the stud checked by a professional, it would be interesting to see what that person has to say about it. I hope you decide to let him have a look at it and if you allow it, please share the findings here.

Charles

Yes I have been reading with interest as well. Large amount of force on a small stud running a big face mill at heavy rpms.
But then again he says he's been running the same job for a while without a problem.

Now is it "has run before" a determining factor or has this process always been on the edge of failure...but this time a little less strength on the stud, maybe a little more force on the cutter...material not as easy to cut or a few thousandths heavier cut, maybe part shifted a hair, insert chipped or a chip on side of tool holder.

Something is always the weakest link...beef that link up and there is still a weakest link...although it may lay elsewhere.