Tuesday, February 25, 2014

Tight and Sticky Chuck

My three jaw chuck on the ML7 for some reason was becoming more and more of a fight to use with the T-wrench. I had no idea why other than swarf had entered into the gears, or binding the jaws themselves.
Neil had been around and used the lathe and  being one who works with them often he agreed. He quickly removed the jaws and cleaned out the worm drive and ways of the jaws it freed it up a little.

Some weeks later I had a small job to do and again the jaws were tighter than they should be to move. So the plan was to one day remove said chuck from the face plate and clean and service completely. We all know that's not what happened it took three days.

Removing the jaws then the chuck from the face plate no problem. .

Remove the back plate screws from the chuck easy, while doing so I noticed what appeared at first to be rust marks around the edge of the body and plate. Now even as a novice I know rust is not a good thing for a chuck. I scrapped at it and found it to be sticky ?????

Outer screws are retaining screws for T-wrench gear
Inner screws secure the back plate
Note:- Top of photo rust/goop














I removed the securing screws for the T-wrench pinion gears which Neil had pointed out were miss-matched in location, removed those and again I spotted a substance looking much like rust in the gear area.

Time to work out how to remove the back plate and worm drive. Using a brass drift and light taps in between each way gap there was movement. I continued going round each a little at a time, off came the back plate and what a mess. I then continued with the worm gear again some sticky rust looking gloop.

Then it dawned on me this wasn't rust it was wax a great dollop of it in one area around the inner edge of the body of the chuck and gears etc.
There was no sign of  any metal swarf of major worry at all.

Everything soaked in Kero to loosen up the wax and clean all parts even the screws.

Out came the brass wire brush and every gear was brushed to remove final traces of the wax which was caked on. This had the appearance of chain lube or real old thick axle grease but smell of ski wax.

Next  checking the jaws in the ways. On each side of all the jaws a ware mark had formed at the edge of the way and they were tight even without any worm and pinion gear driving them.
Each jaw was checked with vernier against the way it should be in and I found there was no difference to allow smooth movement or play.

I used the disc sander with 120grit holding each jaw verticle 90deg and removed the mark from each side until each one would slide with slight force through the ways. I then using a Diamond plate lapped them to a finish.  Each jaw was tested with all gears assembled as I proceeded with each jaw individually.
checking individual jaw movement

With everything clean washed of any grit again all was re-assembled with a light oil and tested all working much better.

I wonder if the chuck may have been dropped prior my purchase?? It certainly had never been maintained or cleaned of the wax or fine grit.

Arrows show wax deposit
Note: Dark area is where wax had been sitting around outer edge


Arrow showing wax



Ring Gear
Worm drive
  The ring gear and worm drive are one unit just reveres sides.

Worm, ring and pinion gear

Back plate and screws
 Above photo was prior cleaning.

After assembly and mounting back onto the face plate I did use the dial indicator to check for run out on the body of the chuck a reading of .0005" I then check run out on a known true bar and reading was .0002"


Always make sure dial indicator magnetic base is switched on or not near the edge so you can knock it off onto your lap and down to the floor. Dial indicator needed then some repair but is working well.


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