3-Jaw Chuck is Jammed/Frozen

ps15 · Nov 10, 2018

I bought an old (very old) Cushman 3 jaw chuck and I cannot back the jaws out. The jaws are in the closed position and they open smoothly for about a 1/8 of the way out and then they jam. I suspect a chip pack in the scroll or rusted chips?

I soaked it in mineral spirits and then took it apart with the jaws still in to clean it as much as possible. I have opened and closed the jaws repeatedly while washing mineral spirits through the chuck. Is it possible to take the scroll plate out while the jaws are in? Also jaw #3 can be tapped forwards and backwards much more than the other jaws, does this mean anything?

Next I will try to soak it in special rust remover that does not harm the metal. Would like to see this classic chuck working again. Advice much needed, thank you.

Mark Rand · Nov 10, 2018

Usually you can remove the back of the chuck and then take out the pinions and scroll. Have a very good look at the chuck for ways into it before resorting to chemical cleaners.

ps15 · Nov 10, 2018

Mark Rand said:
Usually you can remove the back of the chuck and then take out the pinions and scroll. Have a very good look at the chuck for ways into it before resorting to chemical cleaners.

You think it is likely that I can remove the scroll while the jaws are still in the chuck?

moonlight machine · Nov 10, 2018

It's easy to remove the pinions and scroll on a Cushman chuck. Just un do the back, remove the pinion retainers. They just unscrew, I have seen some that use a flat blade screwdriver and others that use an allen wrench. Then push the pinions out and turn the chuck over and the scroll will fall out.

lars66 · Nov 10, 2018

No idea if all Cushman chucks are alike but my old 12" 3 jaw has 3 locations on the back for pushing bolts to release the back plate.

michiganbuck · Nov 10, 2018

QT [#3 can be tapped forwards and backwards much more than the other jaws, does this mean anything?]

Perhaps it had a crash and #1 and #2 got whacked harder. likely a hone to the slot for perhaps .0002 removal would/might fix it good.
Perhaps you could turn the scroll clear on its clearance and knock out the stuck jaws with turning the scroll open as you go. I would likely use my brass slugger and tap with a smallish hammer.

With jaws turned to most closed you might JoBlock check the slots to find a tight place and hone.

scroll removed first would be best if possible.post #4 moonlight

JST · Nov 10, 2018

Even before you do that, you can likely look through the jaw slots, and see the scroll as you turn it with a pinion. If something is jammed in there, you may be able to pick it out with a scriber.

But it is a good idea to disassemble any chuck from time to time for cleaning, so you may as well if it is not on a machine. Normally that gets more crud out than is possible without disassembly. Chucks collect swarf like crazy, and if not cleaned, do tend to jam up.

Boring operations tend to crap up a chuck worse than most other operations. The swarf is thrown outward into the jaw teeth and scroll,

ps15 · Nov 10, 2018

moonlight machine said:
It's easy to remove the pinions and scroll on a Cushman chuck. Just un do the back, remove the pinion retainers. They just unscrew, I have seen some that use a flat blade screwdriver and others that use an allen wrench. Then push the pinions out and turn the chuck over and the scroll will fall out.

I had the back plate off and there were no retaining screws for the pinion gears, they just sat in a recess. I banged the chuck, scroll side down, on a wood work table a few times thinking the scroll would drop out. It did not.

moonlight machine · Nov 10, 2018

ps15 said:
I had the back plate off and there were no retaining screws for the pinion gears, they just sat in a recess. I banged the chuck, scroll side down, on a wood work table a few times thinking the scroll would drop out. It did not.

Are the jaws open enough to see the scroll? if so just use a wood dowel and a hammer, it went in, it has to come out.

ps15 · Nov 11, 2018

I managed to tap the scroll out. All but 2 of the guide teeth on jaw #3 had somehow broke off inside the scroll and were jamming it as well as keep the scroll from wanting to drop out. Now I just need to make a new jaw and this classic chuck will be alive again.

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