Myford ML4 change gear modification

[AJAXParticipant @ajax]

I recently acquired a Myford ML4 which came with a limited number of change gears. The final driven gear has an unused keyway, and the leadscrew is not keyed (it has a small flat) and relies on a bush (fixed with a setscrew on the flat) that has a small pin that engages with the side of the gear wheel. All the torque is transferred via this small pin. Maybe that's a good idea, maybe not. I would expect it to be a likely point of failure in the event of a crash.

I happen to have a collection of keyed Myford change gears that could easily be modified to work on the ML4 lathe by adding a small hole for the pin. However, I'm wondering whether it would not be more sensible to mill a keyway slot and fit a key to the leadscrew. By making this one modification I could then use any of the change gears at my disposal.

I would welcome comments.

[AJAXParticipant @ajax]

Continue using the pin or add a key?

[BazyleParticipant @bazyle]

The pin works ok on thousands of Drummonds and a smaller pin on thousands of RanAs. For most people drilling a hole is easier than milling a keyway. Take your pick.
If you need a safety feature fit a brass pin?

[not done it yetParticipant @notdoneityet]

Think about it. The lathe is very likely less than 500W.

How much of that available power is used by the lead screw drive?

Can you drill a hole without breaking a drill bit of that size?

Is that short pin, in shear more, or less, likely to break than a long drill bit, of similar size, waving around?

Do you have the skill to drill a small hole in these change wheels, at the appropriate position, bearing in mind that they all line up at the same distance from the centre line?

The answers to those questions may well lead you to the correct conclusion – as to whether the pin-drives are a cheap and practical drive option.

Edited By not done it yet on 16/05/2022 07:23:56

[DiogenesIIParticipant @diogenesii]

The pins work okay, I've never heard of one shearing in normal use.

You'll have to drill the keyed ones anyway, in order to be able to compound them with the pinned ones.

If you use keys in the drive, there is a danger that the small spindle drive pinion / fixing becomes the weakest link in the train..?

[Nick Clarke 3Participant @nickclarke3]

A reminder that the original Drummond/Myford pins were tapered and only fit from one side.

I would be tempted to not do this with your new pins but use parallel pins held in place with loctite or similar.

[Mike PooleParticipant @mikepoole82104]

In the event of a crash it is nice to only have to replace something cheap and easily replaced. Although Myford do not fit an actual shear pin in the leadscrew drive train there is usually a weak point that will let go first. The pin drive may well let go first on the ML1-4 and the fibre gears usually strip on the 7 series. Although the fibre gears may not have been designed as the drive train protection it is useful that they do fail before anything else. Some people claim that the quadrant for the drive train should be not tightened too much so under an overload condition it will move and unmesh the gears, I would think trying to judge this could result in an unexpected disengagement that will ruin the job. The fibre gears do make an expensive shear pin compared to the simple pin drive on the ML1-4 series.
Mike

[not done it yetParticipant @notdoneityet]

My Raglan LJ used pins to connect together change wheel combinations. Those I made, as I recall, were drilled only part way through at the pin size, so there was no chance that they could ‘fall out’.

I Also took the obvious precaution of completing the hole at a slightly smaller diameter, to enable easy removal of the pin, if required.

Pins were (sensibly?) derived from the appropriate sized shank of cheap/blunt/broken drills.

These pins have worked perfectly adequately for the last several decades. KISS Principle in operation, as usual, I expect. That, or the age-old adage “If it ain’t broke, why ‘fix’ it?” applies.

[Bill Davies 2Participant @billdavies2]

Ajax, assuming that you would want to key the intermediate gears, they would have to have bushes with a key, through each pair of gears, to bear on the non-rotating shafts on the banjo. There would seem to be little benefit in keying the final gear to the leadscrew, if the previous gears transmit their power via pins.

Bill

[Howard LewisParticipant @howardlewis46836]

When I helped a chap to get his ML4 up and running, one of the things that was needed was another 60T gear.

The only one available was from a ML7.

One of the existing gears was mounted on a stud and drill through to act as a jig for drilling the 3/32" hole into the 60T gear, opposite the keyway..

Once this was done, by using 20T gears as drivers, it was possible to arrange a fine feed, 20:60 / 20:65 / 20:60

The 20:65 intermediate Idler ensured that there was no clash between the 20:60 compound meshes..

With the 8 tpi Leadscrew, this gave a mechanical feed rate of about 0.004" per rev. This provides quite a good surface finish on finishing cuts.

Howard

[GeorgineerParticipant @georgineer]

Posted by Nick Clarke 3 on 16/05/2022 07:44:59:

A reminder that the original Drummond/Myford pins were tapered and only fit from one side.

I would be tempted to not do this with your new pins but use parallel pins held in place with loctite or similar.

I can't answer for the Drummond (though I have my suspicions) but the Myford used parallel pins of 3/32" silver steel. I have this in original Myford paperwork somewhere. Not Loctite – you want to be able to remove the pins, so nothing tighter than a sliding fit. .

The Myford way was to drill blind holes in the gears and collars, which trapped the pins in place. If you drill through-holes, the pin will work its way out and let go in the middle of a cut. Don't ask me how I know.

Ajax, I have used the pin drive system on my father's and then my own ML4s for over fifty years and it never caused the least problem that wasn't of my own making (see above!).

George

[AJAXParticipant @ajax]

Posted by Bill Davies 2 on 16/05/2022 11:07:17:

Ajax, assuming that you would want to key the intermediate gears, they would have to have bushes with a key, through each pair of gears, to bear on the non-rotating shafts on the banjo. There would seem to be little benefit in keying the final gear to the leadscrew, if the previous gears transmit their power via pins.

Bill

That's another consideration. Thanks.

[AJAXParticipant @ajax]

Posted by Georgineer on 16/05/2022 18:02:17:

Posted by Nick Clarke 3 on 16/05/2022 07:44:59:

A reminder that the original Drummond/Myford pins were tapered and only fit from one side.

I would be tempted to not do this with your new pins but use parallel pins held in place with loctite or similar.

I can't answer for the Drummond (though I have my suspicions) but the Myford used parallel pins of 3/32" silver steel. I have this in original Myford paperwork somewhere. Not Loctite – you want to be able to remove the pins, so nothing tighter than a sliding fit. .

The Myford way was to drill blind holes in the gears and collars, which trapped the pins in place. If you drill through-holes, the pin will work its way out and let go in the middle of a cut. Don't ask me how I know.

Ajax, I have used the pin drive system on my father's and then my own ML4s for over fifty years and it never caused the least problem that wasn't of my own making (see above!).

George

George (and others) thank you for the information.

It appears the consensus is to use pins and holes and not to bother with keys. I'm happy with that as it's the easier option.

I have some low-strength Loctite (about 6 unused bottles if I remember correctly!) so I will probably use parallel pins and the through-hole option.

[Nick Clarke 3Participant @nickclarke3]

Apologies – I was thinking of the Myford M-Type (a Drummond design) and not the ML series – but why might you ever need to remove a pin? – I thought each wheel had two holes in it one with the pin fixed in and another empty for the pin of another wheel to fit into when compounding.

[GeorgineerParticipant @georgineer]

Posted by Nick Clarke 3 on 17/05/2022 08:40:52:

… why might you ever need to remove a pin? …

Three reasons spring to mind. First, for convenience in storing unused wheels. Second, to allow idler wheels to rotate freely. Third, it reduces the number of pins you need.

The Myford pins, though tiny, had beautifully domed ends.

George

[HopperParticipant @hopper]

I have converted some keyed gears to the Drummond-style tapered pins on a number of gears that came in a box with the Drummond lathe. No problems at all. Just used an existing pinned gear as a drill guide. Never found the need to remove a pin. They stack easily because each gear has a pin and a hole set at 180 degrees so they fit together. For an idler gear, I always put another gear on the stud with it as a spacer anyway.

Making my own tapered pins was an interesting exercise but they worked well, as I had the correct reamer in the box with the gears. (And I even domed the ends in the proper way!) That said, parallel pins and Loctite is defo the easier way to go! And less likely to cause cracking in the very small 20 tooth gear where there is not much "meat" and the tapered pin can wreak havoc if tapped in too hard.

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