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Broken live center in lathe crash

wmpy

Member
We had a crash today that broke the shank of a MT4 live center. I was hoping to get some help figuring out what happened. It appears that the live center loosened up and was hanging out of the tailstock when the drill came in and smacked it. I just can't figure out how the live center could have loosened up. We've made probably thousands of parts since this center was put in the machine. There's a bolt used to eject the center from the Morse taper. I thought it might have loosened up and pushed the center out, but it's tight. The machine has been holding close tolerances without issue. If the center was even a little loose, I would have expected sizes to be moving around. I'm stumped on this one. Pics are below.

IMG_0493.jpgIMG_0494.jpgIMG_0495.jpgIMG_0497.jpgIMG_0498.jpg
 

mmurray70

Member
Morse tapers will do that sometimes. When you want them to come out they will stick like crazy. When you need them to stay put they tend to fall out, usually at worst possible time too.
 

wmpy

Member
Morse tapers will do that sometimes. When you want them to come out they will stick like crazy. When you need them to stay put they tend to fall out, usually at worst possible time too.

Thanks. I had never seen it happen before, but I was afraid of that being the case. I had considered using some retaining compound to keep it from coming out. I don't think I could ever remove the center without heating it up, though. And I don't think I could heat it up without cooking the grease in the bearings.

Surprisingly, the center still spins fine despite being nearly broken in half. Just stick it back in and run it, right? :)

Also, props to Riten for giving me a discount on a replacement by sending my broken one back. Their trade-in program is a nice deal.
 

wmpy

Member
You better check your machine. That takes some serious force to break that in half like that.

Yeah, I'm about to go do an alignment on the machine. I expect the turret and the tailstock to be have moved. Thankfully, the Morse taper socket where the center plugs in to doesn't show any signs of damage. That part must have been hardened.
 

Milland

Active member
Yeah, I'm about to go do an alignment on the machine. I expect the turret and the tailstock to be have moved. Thankfully, the Morse taper socket where the center plugs in to doesn't show any signs of damage. That part must have been hardened.

What I'm wondering about is the fretting damage (or whatever that is) on the surface of the live center Morse taper. That alone might have been a cause (or result?) of a poor fit to the tailstock, and could have directly contributed to the loosening prior to the crash.

Was that center used on other machines, or did it live in that specific lathe?
 

wmpy

Member
What I'm wondering about is the fretting damage (or whatever that is) on the surface of the live center Morse taper. That alone might have been a cause (or result?) of a poor fit to the tailstock, and could have directly contributed to the loosening prior to the crash.

Was that center used on other machines, or did it live in that specific lathe?

I did notice the marks on the shank. They didn't look that bad to me. I wouldn't expect the shank to look pristine, so I don't know... I chalked it up to normal wear marks. You might be on to something. I'm just not sure how to investigate it further.

The center was not used on any other machines, but we do take it out if we don't need it to avoid crashes.
 
Check the Morse taper in the tailstock with another tool and Prussian blue to ensure it has full contact.

A precision Morse taper master would be ideal but in the real world; anything in good shape should work.
 








 
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