wrecking a 3-jaw?

J

jaychris

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I've seen some references in a few different places to "wrecking" or "ruining" a chuck, mostly in the case of a 3-jaw. Some of the cases I've seen mentioned involved a cutoff operation going bad or some other general machining operation that somehow ended up ruining the jaws or the chuck to the point where it was replaced. None of these cases involved the tool or post crashing into the chuck or anything like that and none of them really described what "wrecked" meant.

So ok, now that I've given a vague description, what would constitute "wrecking" the jaws on a 3-jaw chuck (or the chuck itself).

The first thing I'll mention is that I'm relatively new to lathes and machining in general. I try not to do stupid stuff and I have a lot of respect for the power of these types of machines. I own a 14x40 ChiCom lathe and so far, the projects I've done have come out pretty well.

The reason I am asking the question above is that I was parting a 2" piece of steel (303 SS). At some point, the cutoff tool caught, twisted, and snapped off. After that, my 3-jaw seems to have a lot of runout. I tested a ground test bar in the chuck jaws and came up with a little over .006", which seems like a lot. I've also noticed that the scroll seems to be pretty tight in the same place as I open and close the jaws, whereas before, it was very free and easy. I pulled the jaws (indexed marked first) and thoroughly cleaned the scroll drive and the jaws themselves, but it still hits a spot where it takes a fair bit of effort to turn the chuck key. I'm wondering if I may have done something to the jaws in the aborted parting operation and if so, how it might be fixed. Do I need to true up the jaws with a tool post grinder? Or do I need to start shopping for a new 3J chuck (and maybe upgrade).
 
You've pretty much answered your own question. If you can live with 0.006 RO, fine. If not, you have a new doorstop.

The jaws and the slots/grooves they ride in probably got deformed and, the uniformity of the scroll was probably damaged too.


BTW: This stuff happens. It's like riding a motorcycle... there are two kinds of riders -those who've never dropped a bike -and those who will.


Ray



jaychris said:
I've seen some references in a few different places to "wrecking" or "ruining" a chuck, mostly in the case of a 3-jaw. Some of the cases I've seen mentioned involved a cutoff operation going bad or some other general machining operation that somehow ended up ruining the jaws or the chuck to the point where it was replaced. None of these cases involved the tool or post crashing into the chuck or anything like that and none of them really described what "wrecked" meant.

So ok, now that I've given a vague description, what would constitute "wrecking" the jaws on a 3-jaw chuck (or the chuck itself).

The first thing I'll mention is that I'm relatively new to lathes and machining in general. I try not to do stupid stuff and I have a lot of respect for the power of these types of machines. I own a 14x40 ChiCom lathe and so far, the projects I've done have come out pretty well.

The reason I am asking the question above is that I was parting a 2" piece of steel (303 SS). At some point, the cutoff tool caught, twisted, and snapped off. After that, my 3-jaw seems to have a lot of runout. I tested a ground test bar in the chuck jaws and came up with a little over .006", which seems like a lot. I've also noticed that the scroll seems to be pretty tight in the same place as I open and close the jaws, whereas before, it was very free and easy. I pulled the jaws (indexed marked first) and thoroughly cleaned the scroll drive and the jaws themselves, but it still hits a spot where it takes a fair bit of effort to turn the chuck key. I'm wondering if I may have done something to the jaws in the aborted parting operation and if so, how it might be fixed. Do I need to true up the jaws with a tool post grinder? Or do I need to start shopping for a new 3J chuck (and maybe upgrade).
Click to expand...
 
I have to ask, how close were you cutting to the chuck? Answer this and you can pretty much tell how much damage you inflicted on that poor chuck. If you were close, not much damage and it can probably be salvaged. 3 or more inches out and as Dave said, nice Doorstop.
 
I was probably right around 3" out or so. I try to part as close to the chuck as possible, but in this case, I did not plan well enough.

Thanks for the advice and assessment though, I really appreciate it, even if it doesn't look good for me. I don't mind looking at a new chuck (it was in the back of my mind anyhow), but I would hate to waste a lot of time and energy trying to resurrect something if it's likely a lost cause.
 
It's always worth looking into. Maybe you can rotate the jaws to different positions (keeping them in the proper 1, 2, 3 order), checking them for flatness etc... At the very least, you'll learn about how to closely inspect something and learn about how important tolerances are. When all you have are lemons, make lemonaide. These things happen and I'd be lying if I said it never happened to me.

BTW: 3J's are more susceptible to damage because there's more space between the jaws for a piece to get wedged in there and really jack things up.


Ray
 
Jaychris.......Where you using the tail stock for support? I learned my lesson the hard way in high school many years ago.
 
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