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Thread: Freeing up 4 jaw chuck
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15th Mar 2014, 12:09 PM #1Golden Member
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Freeing up 4 jaw chuck
I got a 4 1/2" C&J (Coote & Jorgensen?) chuck with my Hercus 9" lathe. I am pretty happy with the chuck as it feels tight and I have been looking into how to properly centre these things, which shows accuracy can be very good:
I have an issue on 2 of the jaws though as they tend to bind at certain points in each of the screws rotation.
I took the whole chuck apart when I got it, cleaning it out with parts cleaner and compressed air and put it back together with some lubricant, however the binding is not gone and I suspect there may be some burrs on the screws that are binding on the chuck body as the jaws themselves appear pretty clean/clear:
Is it possible to take the screws out of the chuck body so I can check for any foreign bodies in the mechanism and look to deburr any metal if I find it? The screws don't want to seem to come out:
These blocks seem to hold the screws in but I have no idea how to remove them:
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15th Mar 2014, 12:17 PM #2
Hi Neevo,
It could be that the screws are a little tight on the jaws as they are sitting a little high. Can you take a pic of the back of the chuck? The dowels that hold the screws should just be a pressed in part, you should be able to tap them further into the chuck a bit with a soft drift and a hammer. If you go to far you can flip the chuck over and go the other way. You can always use a press and a dial gauge too for a bit more control.
Cheers,
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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15th Mar 2014, 12:42 PM #3Golden Member
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Ueee, I am pretty sure it's a binding issue on the screws as it binds with the jaws out (although binds more with them in).
Here is the back of the chuck:
Haven't noticed before but it looks like the holes on the back of the screw part are actually a different material which would maybe support your thoughts that they are pressed in:
Do you think its possible to press these out? If so I may get them in the vice with a stud to see if I can drive them out a bit. Seems like the holes are threaded, maybe this is so that you can pull them back in to the chuck afterwards?
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15th Mar 2014, 01:37 PM #4Golden Member
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Ew, you were right. The screw dowels are a press in part. I tapped them into the chuck and they moved. Only problem was I think they need to be pulled out of the chuck (out the back) so the screw part can be slid out of the chuck sideways. Now I need to work out how to do that.
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15th Mar 2014, 04:30 PM #5Senior Member
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Hi Neevo, you can remove the pins by tapping lightly on the retaining 'forks' which protrude to hold the screws in place. Just use a fine pin punch/ tap lightly from front of chuck - ensure there is a tube or something similar (maybe an old socket) on the rear of the chuck.
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15th Mar 2014, 05:27 PM #6Golden Member
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I went 1 better and decided to fashion a puller from an old hex bolt, some 5mm plate steel and a socket:
Made the steel plate big enough for a 22mm socket:
Managed to get it all apart:
The edges of the grooves where the jaws slide were a little cut up:
So I took to them gentle with a file and sandpaper, simply to knock the bumps off the edges. Also the edges of the grooves where the screw ran were a little rough so I did the same to get rid of any potential issues there also:
So, the verdict? Well I have 3 out of 4 jaws working perfectly. Turns out the screw on one of the jaws is a little bent in the middle meaning its never going to run true, so for the moment I have put it back together and will deal with the binding on that one jaw.
All in all, not a bad 1/2 days work... now back to the F1
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15th Mar 2014, 05:37 PM #7Cba
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1) Compressed air should NEVER be used to "clean" a chuck! You just embed chips and dust deeper into the innards. Never again use compressed air to clean a chuck.
2) When you say you "put it back with some lubricant" that worries me. Do NEVER use oil or grease to lubricate a chuck. Oil will just fling in your face by centrifugal force. Grease will just ensure that as many chips and as much dust as possible will stick to it and cause binding. To lubricate a chuck, use either good old plain dry cheap graphite powder, OR a special very thick and sticky purpose made and usually expensive chuck grease.
3) To properly clean your chuck, you MUST take it 100% apart. The screws and yokes must come out. Normally they are very easy to remove. But from the pics your chuck looks pretty old, little used if at all, and pretty gunked up. Use a pin punch from the screw side to drive out the yokes towards the rear of the chuck. Then carefully wash everything, if necessary use a solvent.
4) Under NO circumstances try to lap the sides of the jaws, these must be tight. Only cheap new chucks and worn out chucks have loose jaws. If there are still burrs from manufacturing, you can carefully break them with a fine needle file (aka Swiss file). But do NOT file surfaces or you loose the chuck's precision.
Sorry for the many "must" and "never", but there are certain red flag things when it comes to handling good chucks. Chris
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15th Mar 2014, 05:51 PM #8Golden Member
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Thanks Chris. I put it back together with WD40 so may need to clean that out and swap it for graphite powder. It's all back together now and working fine except for 1 screw which is not 100% straight and so binds at one point in its rotation. Tried to bend it back but couldn't so may have to live with that.
Cheers for the tips. Will bear them in mind next time I do some chuck work.
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15th Mar 2014, 07:18 PM #9Senior Member
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Well done Neevo. Chris's comments notwithstanding.
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