Avoiding stuck chuck - intermitterent cuts

A picture of the Drummond system I use

The block of wood sits on the ways and catches a jaw a 3 O'Clock while the thin bar in the pulley oil hole can be seen

With backgear engaged the bar turns the chuck backwards(clockwise) and the chuck easily unsticks from the spindle nose

Take great care when using any method of locking the bull wheel on a Myford Super 7 whilst using force to free a stuck chuck as there is only a small woodruff key (item H22 on the exploded diagram) that secures the spindle and bull wheel together. Keyways, especially in cast iron or heat treated steel are stress raisers and excessive force or shock loading could easily cause serious damage.

Take precautions to prevent the chuck getting stuck e.g. lubricate the spindle end with anti seize compound and never "spin" the chuck onto the spindle at speed or with any undue force.

Lambton:

Good point - although my understanding (and reading of the diagram in the S7 manual) is that it is the bullwheel that is keyed to the spindle by the woodruff key (H22); the pulley is connected to the bullwheel by the backgear key (H5).

So, ideally should we be looking for a method that doesn't involve the pulley, the bullwheel or the backgear? Perhaps by gripping the spindle tail in some way?

Incidentally, the manual does stress the need for cleanliness and to oil the spindle register.

The Myford Super 7 has already got a spindle lock, at the left hand end of the headstock, at the rear, a "bolt" that slides in. Part no A2751 - Pulley lock assembly item H32 in the diagram

Ega,

I clearly stated the key connects the spindle to the bull wheel.

Robbo,

The pulley is only connected to the spindle through the same key in the bull wheel. The pulley is free to rotate on the spindle until the back gear key ( item 81 part number A2002/2) is engaged which is the normal position.. So when the spindle lock is deployed the back gear key and the woodruff key both take the load. No problem with this under normal conditions of chuck changing but neither keys are designed to cope with brute force .

Lambton:

My apologies; I clearly misread what you wrote. Needless to say, I agree with what you say to Robbo.

Thinking about this I wondered whether the spindle lock is or should be engineered so as to give way before either the backgear key and the woodruff key.

This is an area where prevention is very much better than cure.

Thanks for the replies and discussion.

Ega thanks for the photos and spanner idea - I will investigate how that might apply to my lathe

A friend used to have a very early, cantilever bed Myford, and he used the backgear method to lock the mandrel for chuck removal.

He soon had a selection of gears with missing teeth, or split from the locking pin hole into the bore of the gear.

My lathe (Engineers Tool Room BL1 2/24 (Warco BH600 or Chester Craftsman are virtually identical) has screw on chucks, with two safety dogs for reverse running. Both chucks are large enough to be able to drill a radial 8mm hole into the backplate. A piece of 25 x 8mm flat bar, about 250mm long, has a boss welded onto the end. This boss is drilled and tapped to take two grubscrews. The grubscrews clamp a short piece of 8mm dia. Silver Steel in place.

Once the safety clamps have been removed, with the belt tight, inserting the Silver Steel into the 8mm hole, the first smart smack on the end of the flat bar, (wide face vertical) with a Copper/Hide mallet, usually slackens the Chuck. Tthe same system is effective for the ER collet chuck backplates.

This relies on the inertia of the mandrel, without putting any load onto keys, gear teeth, or chuck jaws.

Howard

Typo edited out

Edited By Howard Lewis on 14/12/2015 15:52:23

Back when I had an old Brit. lathe with screw-on chuck I just put a length of wood, say 2"x2", crossways in the chuck, and wacked the timber, use a hammer or another bit of wood. This always worked and put no strain on any gears.

I understood everything except this bit.

Can anyone fit these safety dogs to any chuck ?

Are they pins that connect the chuck to the headstock to prevent it unscrewing ?

Can't find anything useful on google - dogs just give turning between centres. Any other keywords I can search on ?

Bill

Edited By Bill Wood 2 on 17/12/2015 08:16:19

Oil setting like glue? Well, almost all lubricating oil is made of mineral oil, which has been lying around underground for millions of years. Anything which could oxidise has done it eons ago and turned into tar. If you use vegetable oil such as castor or linseed, then eventually it can harden, which is why such oils are not used in ordinary cars, etc. Racers who renew oil every meeting are different.

The reason that chucks stick in this way is friction. The application of repeated loads from an interrupted cut (etc) knocks the chuck tighter and tighter. The finer the pitch of the chuck thread, the more this will happen, but fine threads do stay tight longer if the chuck is turned backwards.

Hope this helps

Cheers, Tim

It may not be possible to fit the safety dogs , as I call them, to every lathe.

On my lathe, Engineerrs Tool Room BL12/24 (similar to Chester Craftsman, /WArco BH600 / BH900 ) the chuck backplate has a short parallel portion which butts up against the flange on the Mandrel. This parallel portion has two, diametrically opposed, tapped holes, each of which is used to secure an angle "bracket" , one end of which locates behind the flange on the mandrel. In this way, if the chuck tries to unscrew when running in reverse, the dogs prevent the chuck uncsrewing far enough to come off.

If I knew how to post, I'd take a picture and post it on here!

If this can be applied to the OP's lathe it will only prevent the chuck from unscrewing.

The problem here is that, currently, it WON'T!

If you have a mandrel handle, you could try putting a wood block, as shown in the picture at the start of this thread, under a chuck jaw, and using the mandrel handle, turn the mandrel briskly backwards, so as to hit the jaw hard against the block . After all, this is the process that hammered the chuck up tight, so a little low speed hammering in reverse may loosen it. I would not suggest doing this under power, unless you have a VFD with a JOG facility, which still leaves you able to remove power immediately.

Howard

Using the motor to spin the chuck backwards in direct drive runs the risk of damaging the mechanism that locks the pulley to the spindle. I have not stripped my pulley down to know how strong it is but it may be less strong in reverse than forward. Damage here may be more trouble than broken back gear teeth. If I had a really stuck on chuck I would find a way to lock the spindle where it sticks out of the back of the headstock to avoid stress anywhere inside the headstock.

Martin

If the chuck sticks due to friction rather like the way a railway locomotive wheel sticks to the steel track then all you need are some wet leaves..........

Thanks for all the help.

Have got some rotten wet leaves in the compost bin and will coat the threaded headstock nose prior to mounting the chuck in future.

Bill

Never-Seize on the mandrel threads works for me. Less mess than wet leaves too! All I need to do to remove the chuck is put a pice of wood between the jaws as a handle and give it a good yank.

Also, when taking heavy interrupted cuts (currently making a toolpost out of a 3" square block of steel, yikes) I use an old trick from LH Sparey's seminal book "The Amateur's Lathe". Take a two-foot length of wood, say 1" x 2" in cross section and use it as a brake by jamming the lower end of it behind the bed below the chuck and then push upwards gently on the other end so the side of the wood rubs on the chuck. Watch out for chuck jaws that stick out and keep the wood on the headstock end of the chuck body. This acts as a shock absorber and stops the chuck from rattling too and fro as the cutting pressure is released and then taken up again. Works well for me.

For Myfords, Sparey's other book, "A Man and His Lathe" has drawings in it for a simple C spanner spindle lock. The C spanner is cut from 1/8" flat plate and has a pin that sticks out sideways to engage with a hole in the drive pin plate/bull gear. The C spanner handle bears on the headstock casting. So no stress on backgear teeth.

Merry Christmas to all. Got to go eat turkey now!