Removing a stuck chuck.

No apologies for the rhyming title!

As some of you know, I have been repairing a broken back gear on a Mellor lathe that I am restoring. After looking at the evidence, I think the damage has been caused by locking the back gear to remove a stubborn chuck.

I haven't used a lathe with a back gear and threaded chuck before so my question is, is there an accepted way removing a tight threaded chuck or alternatively, stopping it locking in the first place?

Many Thanks, David

Anti seize compound on the thread will go a long way to stopping stuck chucks. As will cleaning swarf out of the internal chuck thread with the spring part off a paperwork "bulldog" clip, sharpened to a point on the ends to get into the thread V.

Don't use the backgear to lock the chuck when unscrewing it. Not familiar with your lathe,but with Myfords it is common to drill and press in a stud into the bull gear then make a special spanner out of flat plate that engages with the stud and butts up against the casting. Was one for a Myford in MEW a couple years back.

As for turning the chuck to get it undone, chuck key is ok if the chuck is not jammed on. If it is tight, I use a length of wood through the chuck jaws for leverage.

Gentle heat ! may be boiling water. DO NOT use the back gear ! Noel.

A block of wood on the lathe bed will hold the chuck

Then apply steady pressure via the spindle or backgear

Do not whack anything, that's why things break

If you find a non damaged part of the backgear, rig up something to keep a decent steady pressure on the spindle nose unscrewing, and go for a cup of tea

(A bit like with releasing a car balljoint, put it under pressure and let nature take its course)

Edited By Ady1 on 15/01/2023 11:15:33

The (more recent?) Super 7s have a spindle lock built in that seems to be little known.

A bit of hex bar of a size for which you have a long spanner, held in the 3 jaw, or square bar for 4 jaw, is an easy and safe way to apply torque to the chuck with the aforementioned spanner. Maybe an impact driver couyld then be used to loosen the chuck without having to lock the spindle?

As it's all coming apart.

Use wood to jam the bull gear and a bar across the jaws to loosen the chuck.

FWIW

Tighten the belt, as much as possible, in the lowest speed position.

Put a medium sized hexagon bar (about 25 mm ) and apply a close fitting socket with a long bar.

Hit the end of the bar hard

Repeated, this may shake things loose

Alternatively, if you have access to an air impact wrench and sockets, use those.

The suddenly applied torque, against the inertia of the motor and drive train, to slacken the chuck, should, eventiually shake things loose

HTH

Howard

Thank you for the replies and the ideas.
I’m afraid that I might not have been clear with my request. The chuck is not on the machine at the moment. My request was how to stop it happening in the future.

Many Thanks David

David from the above, just do not do it up toooo tight and DO NOT use a reverse gear ! Noel.

On my lathe I have a notch for a C spanner which if hit with a small mallet removes the Chuck. As it is in the back plate it dosn't alter the chuck which a spanner on a jaw or on a piece of hex bar can if as like my chuck it is screwed on with 6mm screws. No load on the screws just directly on to back plate and less leverage on the spindle. Do not in any way use the back gear as the gears will be damaged. Just hold the spindle pully etc and a sharp tap on the C spanner will get it free.

David

Edited By David George 1 on 15/01/2023 13:47:32

Just for information I recently went through such a problem on an old Drummond that had maybe been unmoved for 10+ years. Spindle was out and only backplate left stuck on the thread. After the obvious methods failed I first made an adaptor on the backplate for an air impact wrench and heated the plate on the gas ring while trying to keep the spindle cold. This didn't succeed.
Knowing the problem is often rust that needs to be 'fractured' I fairly gently hammered round the backplate boss radially for five minutes, and also end on to it. This potentially cracks the rust and stretches the metal, yes even cast iron can stretch as we are talking thou only. Then warmed only with a paint stripper and while the spindle was held in wood chops in the vice a bolt through one backplate hole provided a point to apply tangential hammer blows. This worked after only a few blows. I can now see the rust problem was primarily on the back face of the plate register.

As a preventative I am in favour of dry graphite powder as I think it remains as a layer that cannot flow out like grease does. However it might not have the rust inhibition power for a machine left in a damp shed. Also always best to loosen the chuck a tad before going to bed,

Don't forget. If it is easy to come off, then it will if you use reverse!!

Bob

I recently bought a 3D printed gizmo that comprises part of an internal gear that engages with the ML7 bull-wheel. Another part of the gizmo (sorry, no photo at the moment ) rests on the head-stock casting. Any torque applied to the spindle nose is passed to the bull-wheel via the woodruff key, then via the gizmo's many teeth to the head-stock casting, not via the back-gear teeth.

I haven't yet had to use it in anger but it looks like it would do the trick.

Of course, the ML7 bull-wheel profile is more commonly known (to 3D printers ) than is that of the Mellor bull-wheel.

Best regards,

Swarf, Mostly!

All the above are really helpful.

Thank you, David

..never let the left hand engage the spindle drive before the right hand has told the brain that the chuck is fully home on it's seat..

Routine maintenance. Maybe once a month loosen the chuck a few turns and do it up again. Maybe once a year take it off completely and clean and re-oil the thread.

They jamb because cutting forces tend to overtighten the screw, after which a little rust or gummed up old oil holds it even more firmly. The longer a screw on chuck is left undisturbed on the lathe, the more likely it is to stick.

Dave

Whilst I agree with the first part of this, the backplate must make firm contact with the spindle shoulder before the lathe is started ie don't tighten it under power.

If the chuck is correctly seated it should be possible to use reverse for some purposes eg winding off a die or returning to start position when screwcutting.

I had several lockups on my s7, and even with the spindle lock I was worried about damaging. So since then, which was few years back, oil the nose before fitting and a thin paper oiled washer stops any problems

Some time ago I had a bout of chuck sticking and I was advised to use a copper washer (cut from sheet in my case) between the end of the chuck thread and the spindle face. I also use copper anti-sieze and have had no trouble since. Can anyone suggest why the copper washer would be effective? The chuck gets removed and swapped with a 4J chuck every few days.

Chas

I would be wary about using a copper washer on one of the register surfaces of the spindle nose, my concern would be whether the accuracy would be compromised as the chuck backplates and faceplate are turned in position and inserting a washer may change that reference. Copper being quite soft does tend to compress and spread although in this application I doubt it will be tight enough to squash the copper. It may be worth doing some checks with and without the washer to see if this is an issue. Copper washers and gaskets certainly spread when used on sump plugs and head gaskets.

Mike