Myford ML7RB backgear cluster

[ianjParticipant @ians]

What a bad day ! Managed to strip some teeth off the 17 tooth gear of the 17/53 tooth back gear cluster on my ML7RB lathe.

Is it possible to remove and replace the cluster with out the hassle of removing and replacing the spindle. I live in hope!!

Ian

[ianjParticipant @ians]

[Mike PooleParticipant @mikepoole82104]

Here is a link showing what you need to do, I don’t fancy your chances of getting that apart with the spindle in situ unless you are a gynaecologist, and getting the gear cluster out doesn’t look as though there is enough room to get it passed the spindle. It may be possible to unbolt the whole headstock and drop it out but I think that could well be more trouble than taking the spindle out. Don’t forget the screw hiding down the back gear lever top detent hole.

**LINK**

Mike

[ianjParticipant @ians]

Thanks for the utube link Mike, it confirms what I really thought. Looks like I'm going to have to learn how to reassemble the spindle and bearings, I may be back !!

Ian

[Brian WoodParticipant @brianwood45127]

Hello Ian J,

I had just the same misfortune and I'm afraid the only way of getting to it for access is to strip the lathe spindle.

One reassembly tip I think is worthwhile is to put a scratch mark across the lever and boss of the eccentric that swings the back gear up into engagement. It makes correct alignment a breeze when you come to put it together again later. Also, be aware that there are two grub screws that lock the lever in place on the boss.

And finally, another bit of future proofing maintenance which I have incorporated is to run an end mill down the pivot for the combination gear itself to cut a shallow oil groove rather than rely on the drilled hole to provide sufficient lubrication over the length of the close fit of the two components

I hope the repair goes well for you

Regards

Brian.

[egaParticipant @ega]

Unfortunate indeed! May we know what caused the problem?

[HopperParticipant @hopper]

Posted by ian j on 23/02/2019 09:09:32:

… Looks like I'm going to have to learn how to reassemble the spindle and bearings, I may be back !!

Ian

They are not terribly complicated. Mark the bearing caps so they go back on the way they came off. Four cap screws and the whole shebang can be lifted out. Be very careful on disassembly to capture and note the small shims between top and bottom bearings on each side so they go back in the same place they came out of.

If you measure your spindle play up and down before disassembly you might even be able to tighten the bearings up a notch by peeling off one layer of the shims, if yours has the laminated shims fitted. Not all do.

And put oil on the bearings and shaft before final assembly so the bearings do not start up dry.

Not much to it really. Pulleys and gears and thrust bearings etc can all stay in place on the spindle.

Edited By Hopper on 23/02/2019 12:13:29

[Brian WoodParticipant @brianwood45127]

Ega,

I think it was down to a session of fairly heavy cutting to reduce a rough 4 cornered piece to round, one tooth from the 17 T gear disappeared completely and presumably fell away into the space below the headstock. The cluster gear is 16 DP but made in cast iron and the hammering effect was evidently too much for it. The break was clean with no sign of fatigue.

I have a new one from Myford fitted now, but the materials used are still the same and I am in the process of cutting a new 17 T pinion on a short shaft in phosphor bronze to salvage the old component as a spare.

Regards

Brian

[HopperParticipant @hopper]

Here's one way of smoothing out impact on the back gear when taking interrupted cuts. Credit to LH Sparey for this idea. Crude but it works. Takes up the backlash between gear teeth etc and keeps chuck rotation more constant.

[Brian WoodParticipant @brianwood45127]

Hopper,

Thank you, I'll remember that for the next time; a neat trick. I don't like abusing machinery and I don't recall any unusual added noise when the tooth broke off, but it's absence was very soon apparent as the next tooth along took the additional impact from the gap left by the missing tooth

The drive gear from the V belt cluster is in P. Br and I query the design concept regarding the strength of a 17 T cast iron gear in the chain with the anticipated loading that back gearing might be expected to handle; hence my planned salvage with a P Br alternative. Change wheel gearing of that sort of tooth count is usually in steel, much better able to handle the loading per tooth.

Brian

Edited By Brian Wood on 23/02/2019 12:36:14

[egaParticipant @ega]

Brian Wood:

Many thanks for the cautionary explanation.

I am reminded of GHT's Small Rotary Table:

"After a lot of clonk, clonk, clonk, the base was eventually machined and I believed then that an ML7 would turn anything!"

He didn't say whether he used back gear or Hopper's dodge.

I take your point about the use of cast iron but wonder whether the pressure angle has a bearing on the strength of the 17T gear.

[ianjParticipant @ians]

.

Thanks for the replies.

Hopper.The ML7RB is basically a super 7 with the ML7 cross and top slide so its the bronze bearing etc type headstock.

I damaged mine by turning a boss on the face of a piece of 1/2"x2"x4" EN1 MS so similar to Brian it was an interrupted cut and maybe a bit to heavy1

Ian

[Jan BParticipant @janb]

Hello Ian J,

The same happened to me last weekend.

I also came to the conclusion that I have to remove the spindle to get access to the back gear. I am thinking of making a new 17 tooth gearwheel in steel instead of cast iron and fit this to the 53 tooth gearwheel. Does anyone know what pressure angle Myford used, is it 14.5 or 20 degrees? I guess it is DP and not Module. Can I use a module gear cutter? The evolvent profile must be the same, or am I wrong?

Jan

[Mike PooleParticipant @mikepoole82104]

Stripping the myford spindle seems daunting but is fairly straightforward once you understand how it works, the method is explained in a number of places and once you have done it you will wonder what there was to be worried about.

mike

[Brian WoodParticipant @brianwood45127]

Jan B,

The gear size is most definitely 16 DP and I would imagine the pressure angle will be 14.5 degrees.

To my knowledge, the only time Myford deviated from that was with the Super 7 spindle and reversing gear complex, all 4 of those are 20 degree to cater for the tooth loading.

Regards

Brian

[ianjParticipant @ians]

Just doing a bit of reading on removing and replacing the spindle. When I replace it are the rear bearings still correctly set for the preload and I only need to adjust the threaded collar on the left to set the front bearing clearance?

Ian

[Brian WoodParticipant @brianwood45127]

Hello Ian,

You will have to draw the spindle out of the bearing cluster to remove it over the bed, so I'm afraid you will need to go though the whole set up procedure when you put it all back again.

If you have Myford's handbook with the instructions for setting pre-load and bearing clearance, just do exactly as it says and all will be well. The job is made so much easier if you have a hook wrench to set the bearing cluster collars correctly

Regards

Brian

[ianjParticipant @ians]

Thanks for that Brian.Yes I have the hand book, hook spanner and even a peg spanner for the LH adjusting collar. Just need to buy the new gear cluster and get on with it!

Ian

[Brian WoodParticipant @brianwood45127]

Hello again Ian J

Last word if you need it.

You do know about the method of holding down the oiling wick in the bronze bearing against it's spring during spindle re-fitting and how to get access to do so?

Good luck with fitting the replacement gear. They are much more utilitarian in appearance now without the six nicely shaped lightening slots in the 53 tooth part; I was rather disappointed to see that.

A silly notion I know and had I made it as a spare part I would have done the same, but it is another example of a quirky little bit of the overall design process in creating the lathe cast aside in the name of progress!

Regards

Brian

[ianjParticipant @ians]

Brian thanks for the reminder about the needle trick to hold the wick in position.

Yes I noticed the new gear cluster now don't have the lightening slots, I suppose before fitting a new one they could be milled out.

" I am in the process of cutting a new 17 T pinion on a short shaft in phosphor bronze to salvage the old component as a spare. "

How do you propose to secure it to the 53 tooth gear?

You don't fancy making two while your at it ?

Ian

[Brian WoodParticipant @brianwood45127]

Hello Ian J

The non gear end is going to be inserted into the 53 tooth wheel [after turning off the damaged tooth] as a shrink fit and further secured with a two small pins drilled axially into the joint interface. Then the bore will be carefully sized to fit the spindle it runs on.

I note your smiley!

If it was a financially sensible operation I would make another for you but I had to buy the cutter just for this job and then of course the section of P Bronze; taking those outlays together with all the machining work including cutting the gear you could easily afford to buy at least two more spares from Myford even if I barely charged you for my time.

If you have the resources it is not too difficult, it just isn't cost effective to make one offs when you aren't fully equipped to do so.except just for the satisfaction of making your own expensive spare part!

Regards

Brian

[Brian WoodParticipant @brianwood45127]

And I have just remembered another little thing–when you have your new gear cluster fitted and the mandrel back in position, ready to test the back gear in other words, it will sound noisy and you will wonder at what you have done!.

Lift the eccentric lever to exceed the upper stop drilling and with the lathe running at slow belt speed hold the eccentric hard up to bed the new gear in . It will very quickly run quietly again as all the new edges are smoothed off and settle down with the existing gears.

This was the method used by Raglan of Little John lathes fame to bed in the screwcutting gearing on new lathes by no less a person than John Stevenson when he worked for them as a young man. After that short running in period with the selector levers hard up beyond their stops, the oil was drained, fresh oil added and the lathe was added to the stock for sale

Regards

Brian

[ianjParticipant @ians]

Just an update,Fitted replacement back gear cluster this afternoon.All went well once I remembered the grub screw (H26) which locks the back gear eccentric screw(H71).

I get the feeling there may have been a missing tooth ever since I've had the lathe as it was always noisy/rattling when in back gear and now not.

Thanks to all for the advice, tips and encouragement for me to replace it.

PS I managed to purchase a new old stock original part.

Ian

[Mike PooleParticipant @mikepoole82104]

Glad it went well Ian, a bit of a heads up on the pitfalls makes any job less daunting. You tube and relevant forums are great for getting info on anything that needs fixing and what was initially a mystery can end up being straightforward once you know how.

Mike

[NICHOLAS ELLISParticipant @nicholasellis10828]

Has anyone found a way to improve the back gear key, which is so fiddly to get in and out..might be the reason your tooth broke?

[Author]

Posts