As Alecs has said it will and does happen, so DO NOT lock gears to undo the chuck.  Noel.

On 6 June 2026 at 12:24 drnewcomb Said:

Has anyone ever broken a gear (Bull, back, etc.) on a Myford ML7 while removing a chuck? I had a discussion with my mentor about my concerns over using the back gear to lock the spindle to remove the chuck. He replied that it would take so much torque to break a tooth that he wouldn’t worry about it.

That’s a yes and no. If it was new and you were using the flat of your hand and not a hammer the bull won’t break. But consider an ML7 has had multiple owners by now and someone else may have swung the hammer already and that crack is just waiting to propagate.

On 6 June 2026 at 18:20 Andrew Tinsley Said:

…………………..

I have threaded the chuck on the mandrel nose by half a turn and then turned on the lathe at maximum speed! This really jams the chuck on very tightly. ………………………..

Andrew.

Why on Earth did you do that?

The S7 instructions given for freeing a tight chuck was to put a block of wood between a jaw and the lathe bed to stop the chuck rotating. Then, in back gear, try to rotate everything backwards by hand using the belt between the spindle and clutch shaft. This worked for me a couple of times.

Hammers and lathes DO NOT mix.

JA

On 6 June 2026 at 19:06 JA Said:

On 6 June 2026 at 18:20 Andrew Tinsley Said:

…………………..

I have threaded the chuck on the mandrel nose by half a turn and then turned on the lathe at maximum speed! This really jams the chuck on very tightly. ………………………..

Andrew.

Why on Earth did you do that?

The S7 instructions given for freeing a tight chuck was to put a block of wood between a jaw and the lathe bed to stop the chuck rotating. Then, in back gear, try to rotate everything backwards by hand using the belt between the spindle and clutch shaft. This worked for me a couple of times.

Hammers and lathes DO NOT mix.

JA

Probably because a jammed chuck is, generally, so rare that folk don’t read the instructions.

Always assuming they actually have the instructions.

Given the high frustration index when a chuck does jam its the tendency to do teh quick, dirty and obvious with stuff immediately to hand is understandable.

Clive

On 6 June 2026 at 19:16 bernard towers Said:

My S7 has a stop pin for just that job

Hmmm – I used the stop pin on my S7 to attempt to remove the stuck 9 inch faceplate that I had used to shape a large piece of 4 mm MS plate that had involved intermittent cutting on the OD.

I engaged the lock pin, fitted two clamps to the faceplate 180 degs apart near the OD, and heaved on a soft pine 2×4 engaging with the clamps.

Then I felt something give way, the brass/bronze gear/bush that is pressed into the ID of the CI cone pulley had turned in the pulley, the press fit is  the only thing that is holding it.

The condition of the brass gear teeth wasn’t good, caused by the previous meshing of the back gear assembly being too slack.

I bought in a new-old-stock pulley/gear from a company in the Netherlands.

Before fitting it all up, I drilled and tapped 3 equispaced M8 tapped holes down through the bottom of one of the pulley grooves through into the part of the gear which serves as the bush which the pulley/gear runs free on the spindle when in back gear, then turned the lock points off the ends of three long M8 socket grub screws and loctited them in to lock the bush/gear to the pulley ( I have another lathe an old ML7)

Now, before fitting a chuck or faceplate to the headstock spindle, I brush a little NeverSeez onto the spindle thread and location diameter and face.

On the later S7s such as the Big Bore the stop pin engages with the bull gear as Alecs’s arrangement. The pin is held in the headstock casting.

I try to keep the spindle nose and engaging chuck threads scrupulously clean and always store chucks etc working face downwards. Prior to fitting the nose is wiped and then oiled with ordinary ISO 32 oil.

A thought, perhaps the chuck, faceplate etc should be removed from the nose when not in use?

JA

It has been warned MANY times, not to engage back gear, with the pulley still locked to the spendle, so that a stuck chuck can be removed. Effectively, the spindle is in two different gear ratios, so will lockup.

The advice is also given, NEVER to wind the chuck on, under power; to prevent this problem.

Gear damage IS likely (A friend regularly used to do this, on his Myford, and broke a tooth off the gears almost every time!)

Putting a piece of wood, or bar across the jaws, with the spindle in the normal run position, and giving the end ot the wood /bar a whack with a mallet b/ hammer, one or more times, usually frees off the chuck.

Alternatively, grip a piece of hexagon bar in the jaws, fit a correctly sized socket, and give the end of a power bar a whack.

The inertia of the spindle, with the belts tightened, should allow the chuck to free off.

Howard