Breaking gears in a Myford ML7

[drnewcombParticipant @drnewcomb]

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. I just don’t want to be that guy who finds out. I’ve asked someone to 3D print a bull-gear lock for me, so I won’t have to. Thanks!

[alecsParticipant @alecs]

My ML7 came with a couple of teeth missing from the back gear thanks to previous owner using it to remove chucks. And I have seen other instances over the years. It very definitely can and does happen. The back gears are cast iron so those small gear teeth are more brittle than on steel gears. They don’t bend or deform like steel, they just crack right off. You are right to get a locking block made up. Use it religiously.

 

[noel shelleyParticipant @noelshelley55608]

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

[Robert Atkinson 2Participant @robertatkinson2]

As said, they will break. The plastic gear locks work because they are more compliant than the cast iron gear and spread the load over many teeth.

Robert.

[drnewcomb]

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.

 

[Andrew TinsleyParticipant @andrewtinsley63637]

Robert is correct! I trialled a free printed plastic gear lock, which a forum member provide a couple of years ago. They work well and don’t break the bull wheel teeth for the reasons Robert gave.

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. The plastic gear lock undid it with no problems.

Andrew.

[Andrew Tinsley]

On 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

[bernard towersParticipant @bernardtowers37738]

My S7 has a stop pin for just that job

[JA]

On JA Said:

On 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

[Clive Foster]

On Clive Foster Said

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

Page three of “Myford 7 Lathe Notes on Operation Installation and Maintenance also Pictorial Parts List” booklet says “DO NOT OPERATE THE LATHE UNTIL …….. The instructions have been carefully read, and the controls and adjustments are understood”. At least the Myford instructions are easy to understand compared with those for my camera.

If anything goes awry, push the big red button, turn off at the mains, shut down the workshop, fix yourself a coffee, better still a stiff drink, sit down in your comfortable chair and have a long think. Then start taking action or seek advice.

JA

[bernard towers]

On 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.

[alecsParticipant @alecs]

I drilled and tapped a 5/16″ hole in the side of my ML7 bull gear and screwed in a silver steel pin, with a bit of Loctite for luck. Then made a C spanner that fits around the spindle. The pin engages with a hole drilled in the C spanner and the spanner handle rests on the headstock casting.  Ive an idea the design was in MEW. And that disassembly of the spindle was required to drill the hole.

And as Howard found, Never Seez is essential on the spindle nose.

[JAParticipant @ja]

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

[alecsParticipant @alecs]

Ive never removed my chuck when not in use. And never had a stuck chuck, thanks to Never Seez doing exactly what it says on the label.

And that includes after doing some pretty ‘orrible interrupted heavy cuts on jobs that really should have been done on a bigger machine. But needs must…

[Howard LewisParticipant @howardlewis46836]

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

[Nigel Graham 2Participant @nigelgraham2]

I’ve often tried the block of wood and pulling the belt backwards trick… usually unsuccessfully.

I have the same problem on the Harrison L5 as on the much smaller Myford ML7. Both have screw-on chucks, and these fittings look unfeasibly large and heavy for the spindle.

I dodge I have used on the Myford is a bar between the head of the bull-wheel engagement-screw, and the rim of the headstock aperture, then a strap wrench on the chuck, or a long batten between chuck jaws.

That doesn’t work on the Harrison’s enclosed, all-gear headstock but my fitting it with a 3ph motor did result in a short stretch of accessible primary drive-belt.

 

I note Howard’s suggestion to use anti-seize compound, which is really designed to protect against galling and corrosion, but I will try it. My normal practice is to clean and oil the registers and threads.

[old martParticipant @oldmart]

The best way to break teeth is to use the chuck key and a hammer, the shock puts great strain on gears. We use a strap wrench to avoid the shock loading. The 3D printed gear holders are by far the best way to avoid damage to the gear teeth. When the very first 3D printed gear holders came on the market years ago, I decided to make a copy out of 20mm thick nylon on the rotary table, two actually, expressly for the Atlas 12 x 24 which has a zinc gear, even weaker than cast iron. My version has about 14 teeth and can be used for tightening as well as loosening.

[Andrew TinsleyParticipant @andrewtinsley63637]

“Why on earth did I do that” ?

Well I deliberately tried to jam the chuck on the mandrel to test out the printed bull wheel key.  I was absolutely certain that the printed key would:-   A/ remove the chuck without difficulty and B/ would not break any teeth on the Bull gear.

I was fully justified in my confidence. The only way to convince doubting Thomas’s, is to demonstrate in practice, that it is an effective solution to the problem of stuck chucks.

Andrew.

[old martParticipant @oldmart]

That was a severe test of the printed key, Andrew, it did show that the teeth had not been formed hollow.

With my nylon key, which fits on the zinc gear of the Atlas, I normally spin the chuck by hand through about 45 degrees up against the headstock and the inertia does the rest. That works with chucks from 125 to 200mm diameter, not for the 80 or 100mm ones. The weak point would be the fact that the gear wheel is keyed to the spindle. I would like to get my hands on a steel gear blank to use to make a copy of the original one.

The Smart & Brown model A has no easy way of holding the spindle like the Atlas and Myfords, I should look into ways of holding the belt pulleys, double ended to use whichever one is not covered by the belt. Drilling about four locking pin holes in each pulley of about 5/16″ would be easy to do since I can remove the spindle in 15 minutes on this lathe.

[alecsParticipant @alecs]

Made from 6mm aluminium plate, 6061 T6, to a design in MEW some years back. Handy if you don’t have a 3D printer.

[Speedy Builder5Participant @speedybuilder5]

best way – Get rid of an ML7 and get a BOXFORD

[Author]

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