3 jaw scroll chuck - how to dismantle

[RichardG]

I've been given a little vintage 80mm 3 jaw scroll chuck for my simat 101 lathe. It's made by a company called cushman, however, I can't open the jaws. The knurled ring moves about a sixteenth of a turn and I can see the jaws start to open but then it stops, and it's a definite stop as if it's hitting a metal stop. I don't think soaking it in oil is going to help?

Any ideas? Is it a reasonable chuck and worth saving?

 

[TFrench]

I've been given a little vintage 80mm 3 jaw scroll chuck for my simat 101 lathe. It's made by a company called cushman, however, I can't open the jaws. The knurled ring moves about a sixteenth of a turn and I can see the jaws start to open but then it stops, and it's a definite stop as if it's hitting a metal stop. I don't think soaking it in oil is going to help?

Any ideas? Is it a reasonable chuck and worth saving?

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Never played with one like that, but I've pulled a lot of regular 3 jaw chucks apart. Hard to tell, but does it use a key or does the outer ring tighten it, like a keyless drill chuck? If it uses a key, you should be able to get the pinions out - which is probably what's binding. If it's keyless, my normal approach if I'm taking something unfamiliar to bits is to just start undoing stuff and see where it goes. Never failed me yet

 

[okeydokey]

This might sound harsh but if its never going to move I would try the following.
Put the smooth body part in a vice put a long stilson wrench on the knurled part and turn anti clockwise (most likely direction) and it should undo or if you don't have a tough enough vice then two stilsons will do. Or a local garage will have a big vice take you stilson with you and they will probably slacken it off for you - should only take a few seconds. Good luck

 

[Inspector]

I would soak it in kerosene, Varsol, mineral spirits, diesel, 50/50 mix of ATF (automatic transmission fluid) and acetone. After a day or two I would then try it and see what happens. If it moves a little back in the juice and keep working it until it is loose. If it doesn't move then go on to the graunching tools.

Pete

 

[RichardG]

I think it's a write off Soaked overnight then kept going backwards and forwards until if moved a bit more and then suddenly it free'd but quite rough. Taking the jaws out I find the jaws are damaged. Something fell out and disappeared under the bench, I suspect it was a bit of tooth.

Now I've cleaned it up it does work but keeps jamming, the chances of finding a spare set of jaws is almost zero plus it may have damaged the scroll plate as well. Oh well...

 

[jonn]

I think it's a write off Soaked overnight then kept going backwards and forwards until if moved a bit more and then suddenly it free'd but quite rough. Taking the jaws out I find the jaws are damaged. Something fell out and disappeared under the bench, I suspect it was a bit of tooth.
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Now I've cleaned it up it does work but keeps jamming, the chances of finding a spare set of jaws is almost zero plus it may have damaged the scroll plate as well. Oh well...

With something like that I use the one solution I think best when keeping it will be a continuous annoyance: See if it can swim in very deep water! Alternatively put it in a metal scrap bin.