Hardened shaft slips in lathe chuck, help?

[rsr911]

Today I needed to turn down the ends of a piece of hardened and ground 1" precision shaft. I chucked my 6" 4-jaw into my big 4-jaw and dialed everything in nicely. Even though I had the chuck tight the shaft wanted to slip into the headstock. Even taking light cuts didn't help. Finally I was able to combine light cuts with the lathe's top speed of 1800 RPM and basically burn the metal off with a carbide insert (it was coming of in cherry red strands) still had slippage though. Tommorrow I have to do the other side, any suggestions on keeping it from slipping in the jaws? On this job I could put a small tack weld on the large OD so it's can't slip but in the future what are my options? What about putting some soft brass between the shaft and jaws? Clamp type shaft collars? Magic dust? What's the secret LOL!

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-Christian D. Sokolowski

[Evan]

Put a single wrap of silicon carbide sand paper on the shaft, abrasive side in.

[rbregn]

You can use a piece of paper out of your note book also.

[rsr911]

Guess I should have tried the sand paper trick on the outside of the little chuck

I got all set up and dialed in to cut the other end of the shaft today and spun up the lathe. I went to touch off the tool and set my DRO when I suddenly saw the chuck and stock working out of the big chuck. Instinct took over and I got behind the headstock smacking the E-stop as I jumped back, milliseconds later the crash was heard throughout the shop as the chuck collided with the compound before crashing into the floor. Result: One perfectly good 6" 4 jaw cracked in half! Thank God I'd taken refuge behind the headstock, I'm perfectly OK just a bit depressed. Guess I'll have to look for another chuck tommorrow but this time it's getting mounted to a back plate and not in the jaws of a bigger chuck. I've heard it suggested before as a quick way to mount a smaller chuck but my gut told me it wasn't a good idea yet I tried it anyway, I'll stick with my gut next time.

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-Christian D. Sokolowski

[hoffman]

Good Lord man, glad you're alright!
You say it broke it in half?
Sounds like you're lucky it didn't bust the compound or do more serious damage.

[This message has been edited by hoffman (edited 01-08-2006).]

[Derek13]

Eeeesh :S sounds like quite a crash... Glad you're ok!!

So if i take it correctly, a simple piece of paper wraped around a part will help prevent slippage in the chuck?

[rsr911]

Yup, cracked in half when it hit the floor. I don't know about the paper trick yet as I hadn't even taken a cut yet when I saw the chuck start to ride out of the big chuck. I'm gonna bring me digital camera to the shop tommorrow and take a few pics. I'm halfway tempted to make a new steel body for it, they are rather simple after all. To give an idea of the crash, one of the jaw screws was found over 30 feet away! Still searching for one jaw screw retainer. The chuck appears to be cast iron and split right down the middle of the jaw slots. Thankfully the lathe is substantial enough that nothing seems damaged on it and it completely missed the ways, glad the cross-slide is so large I'm sure it's what protected the ways.

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-Christian D. Sokolowski

[BillH]

Cross slide hit? ooooh

[.RC.]

Why not just use the big 4 jaw instead of chucking a chuck in a chuck??????

[japcas]

If I were you I would inspect the 4 jaw chuck that you were holding the smaller chuck with. Sounds like it could have sprung jaws and not holding properly or maybe the smaller chuck wasn't chucked tight enough. There is no reason why the big chuck can't hold a smaller chuck safely like you had it. The chuck doesn't know the difference between it and another piece of stock, so why should it throw it out in the floor?

[JRouche]

Glad yer instincts for survival kicked in and flight took precedence over fight....

Chucking a smaller chuck up with a larger chuck should not be a problem. No difference than chucking up any other job. I would suspect your setup, just based off the story...

A four jaw should grab a smaller chuck, its not a hardened piece, only cast iron, semi steel (whatever the heck that is) or mild steel. I dont think the bodies are hard?

Have you ever had any other work, similar in size, slip out? Maybe just one-a them fluke chuck-ups that just wasnt right.

I am not a machinist but have chucked up plenty of metal and been around many lathes and I have not seen a premature dismount from a four jaw. Been close though with a three jaw due to the work being cocked slightly.

Well, bummer re: the chuck, cool yer reflexes are still functioning...JRouche

[speedy]

Small chuck in big chuck, 1800 rpm. Yikes!!
thats a no no.
You didn`t use a tailstock centre either?
Don`t take my comments wrong; we all cock-up at times.
I`m glad to hear that you are still about to tell the tale Christian.


ken

[rsr911]

Bill, it hit the compound and I think the cross-slide, no damage to either.

Ringer, My large 4-jaw only goes down to 1.25" I was trying to turn 1" stock.

japcas, I though of that but I've turned lots of stock with the big chuck and never had a problem, I'm thinking the hard body of the little chuck against the hard jaws cause the same problem I was having with the hardened shaft. Also the little chuck was flat against the body of the big chuck and the jaws of the large chuck held it almost comletely. While it is entirely posible the jaws sprung a little I'm still not gonna try it again. Between the cost of replacing this chuck and the damage that could have been done not to mention personal injury this is somthing I simply will not do again. Back plates cost less than the cost of the destroyed chuck and D1-8 camlock chucks are easy to change with a lift. If I'd been using the tail stock things would have been different. I bought the lathe more for length and power than swing over bed, the largest thing I've turned so far was only 8" OD. The longest was 54". I'll be doing a lot of work in a 8"x64" envelope as well as a lot of through the headstock work cutting bearing recesses in the ends of thick wall tubing.

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-Christian D. Sokolowski

[rsr911]

J, speedy,

I would have used the tailstock except I couldn't fit my insert tool holder close enough to turn the 3/4" OD I was after. Only way I'll ever try this again is if I bolt the small chuck to a strap of metal and bolt that to the big chucks t-slots. Still with an unfinished backplate on the way it just makes sense to hold off and set it up the right way. It's one thing for a piece of stock to come loose (not that I want to see that happen) but it's so much worse when you destroy a nearly new chuck like I did.

The other bad thing I did was not check the material of the small chuck, I know the big 3 and 4 jaws are steel and rated for the lathes RPM, it's likely the little cast chuck was not and perhaps that contributed to the problem. Everything happened so fast it's possible the little chuck was cracked before is slipped out, all I know is I was out of the way in a hurry.

What do you guys think of machining another body from steel? Aside from holding tight tolerances it really doesn't seem like all that much work and the jaws and screws all seem fine. Might be a fun project even.


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-Christian D. Sokolowski

[This message has been edited by rsr911 (edited 01-08-2006).]

[mark61]

Hard stuff in hard jaws and or making jaws close a little closer to each other is well delt with by wrapping copper or soft brass around the jaws. We have 100's of small pieces of copper or brass laying around the lathes at work. Keep you from chewing up stuff with diamond patterns on chuck jaws too.

mark61