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Bent Lathe Chuck Repair Ideas?

kuksul08

Aluminum
Joined
Sep 21, 2011
Location
CA
Hi all,
I goofed up. I was parting some 2.5" OD aluminum stock in my lathe with a 1/8" HSS tool. Got about halfway in and it climbed up the tool, snapping the tool and getting the material loose in the chuck. I've had this happen once before, and while frightening, nothing happened other than a broken tool.

However it seems that this time, since the jaws were extended so far out, it managed to bend one of the channels in the chuck body. The chuck was still able to be opened & closed by hand, but was very stiff. I deduced this by using an indicator and dragging it along the length of the channel. The other 2 jaws slide freely in and out with about .0005" wiggle, but this one jams once it's halfway in.

The jaws are hardened pretty well, my files don't really touch them. But the body is softer. Do you have any suggestions for how I might fix this and still have a usable chuck? I could file away .002-.003 of material on the underside of the channel, but I'm wary of removing material and how to even do this accurately.

Thanks for any tips.

sIZ3Coz.jpg
 
I think the only thing you could do is grind the bent area and make a new master jaw with a smaller groove.

Probably easier and cheaper to buy a better chuck.
 
I think the only thing you could do is grind the bent area and make a new master jaw with a smaller groove.

Probably easier and cheaper to buy a better chuck.

I think this jaw is pretty nice, just not really intended to be abused like this. Beginner error...

What are your thoughts on jamming a wedge into the end in an attempt to bend the outside of the channel back upwards? I could probably do this with reasonable accuracy.
 
That's only a small chuck, .not worth repairing, .........I can't see a name on it but it looks like a cheapie, .........yes it can be repaired, but it is a hell of a lot of very skilled work, I've not heard of it being done for over 30 years, and even then it was only done on large very expensive chucks.

No offence intended, ........it's one of those jobs that if you're asking the questions you are, ....then it's out of your league.

Scrap it and write it off to experience, .it's called life.
 
Those are bolt on style jaws so keep that chuck and make/buy loads of soft jaws for it and start looking for a replacement rather than try fix it with any sort of precision. It could still come in handy for random parts on the lathe or even as a mill,slotter etc etc "clamp"
 
It might never be accurate again, there will be a tendency for that jaw to tip when tightened, so you'll only get contact with the work at a single point near the base jaw. Workpieces will always be going cocked, and that will be pretty frustrating.

I wouldn't file the tongue as such, I'd scrape it with the tip of the file, only in the affected area. Or maybe lap it a bit with a flat piece sized to fit, backing up a piece of abrasive cloth. This should help determine where it needs scraping. Nonetheless, you're removing metal where none should be removed, creating extra clearance in an already ruined chuck. Like others have said, that chuck could still be great as a welding fixture, etc., but you'd want to loosen it up.
 
Guess I might grind a piece of tough to hard stock to fit the pocket for full width and with about 1/16” high to intersect 1/16 x 1/8" and just clearance the outer most 1/16 edge of the bent leg. Then with pocket well greased add a .001 shim and whack or press it through and try the jaw. Next a .002,.003 till you get it. The 1/8 so the shim portion will pass the tight place .. not just keep getting tighter so having control and go lose once passed....likely set it on an oak block to not damage the other side.

Yes the pound stock well beveled so less chance of shrapnel and a mild heavy hammer for slow heavy whacks.

Still it looks like only .0005 or less ..file-off that amount would not be a deal breaker for the chuck..likely the new specs are that wide. If you can chuck wrench the jaw through it likely is only .0002 or less.

A hone swipe or a blue-up would tell if it is just a bug... and where the tight place is.
 
I would remove the scroll, insert the jaw, and rap it with a hammer or press it in an attempt to bend it back the other way. Perhaps take care to block it up from the underside to limit the deflection to the area you really want bent.
 
WOw! I can't say I have ever seen that before, thanks for posting, it would be the last thing I would even think of. I would not use it for Turning any more, but there are a Million different uses for it, even if one jaw is wonky. Hu's advice is sound, but as long as you are aware of that one jaw's shitty attitude, you should be okay to hold round parts for other stuff.

.0045" is a lot, I think I would also be checking the backside of the slot in the Tee for bend too. But it also seems like one direction, have you run the indicator at different orientations 120º and 240º? Is there a .0045" ding on the backside of the chuck? I would think the taper and back face would have more damage than that part of the chuck.
 
What is the zero? .0725, .076, .077... how does it check nearer to center?

if the outer got bent to tighter .. then logical one could bend it back to more open...
looks like about 3/8 x 3/8 section to whack straight.. that is a lot of stock to whack back.
 
As you can see, toward the center bore of the chuck it is flat all the way until about 3/4 the way down where it starts to tip downwards (3rd photo). I checked the other channels of the chuck and they are all perfect across their entire length, no perceptible change on the indicator.

I will use a different .0001" indicator to check the underside and see if it agrees.

The rest of the parts look fine. The spindle taper on this machine has seen better days as it looks like someone dropped something on it at one point. But I see no damage as a result of this accident.

I like the idea of putting the jaw in the channel and hitting it. This would let me move it the minimum amount required to get it to move freely. Then again, that's some serious steel to move.

It looks like the consensus is what I knew, but didn't want to face. The real answer is a new chuck. Any recommendations for a reasonably priced 6"? I am a hobby machinist, nothing pro level here but I do like to count on the machine to be reasonably accurate.
 
kuksul08: As you have found out, parting off in a three jaw chuck is a no-no. Please use a four jaw independant chuck. I have seen a nice Monarch 16" lathe ruined when a piece crawled upon a parting tool and broke the headstock housing.

JH
 
if a malleable steel body I would bash or file and continue using for regular turning ... if a brittle cast body.... I would only use it as a fixture of things. 3 jaw chucks are very handy mill fixtures, especially on rotary tables.
 
Parttnig off I like to have my tool holding device well centered to the cross and saddle.. often I see one set far to the left so when push goes to shove any slack to tilt. will tilt.. and bang goes the part.

Lucky i have had good luck parting.
 
Get a parallel or other straight edge that fits and actually see how much it is.

The jaws should by feel close fitting where very small amount will fowl it.

It your actions cause damage the chuck may be of type not allowed to discuss but no more there.

With the straight edge you can use a flashlight to back light the meeting of the two to see really what is going on.

You may be able to get a chunk of tool steel (say 1/2 square) and rest it in the slot and after placing some pennies or other soft metal on that soak it gently with the heaviest hammer you have one tap at a time between checks to see if it can be restored.

Otherwise file or stone to fit then knurl effect the rest via center punch to make it not wobble.

Chuck is likely no longer good for good work but still could be servicable while you look for a good one.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk
 








 
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