Myford Super 7 Tumbler reverse lever not engaging

[julianjParticipant @julianj]

Fellow engineers,

Could anyone offer any help with my Myford Super Seven please?

The tumbler reverse lever does not move far enough down to locate the plunger in the bottom detent.

The tumbler gears engage correctly & drive the lead screw in either direction, & the plunger locates in the ‘up’ and ‘neutral’ position. When I move the lever to the bottom position I have to manually hold the lever in place to keep the tumbler gears engaged, the lever just doesn’t move far enough down for the plunger to locate & lock the lever in place.

I’ve enclosed some photos, to my untrained eyes the tufnol gears appear to be fitted correctly & I cannot for the life of me work out what the problem is.

Any advice or opinions would be most welcome. Thanks in advance for taking the time to contribute any information.

Regards,

Julian

[bernard towersParticipant @bernardtowers37738]

Is this a recent thing?  if so whats changed?. Dirt, debris, swarf etc. gear positions are fixed so will not be that. suggest blow out plunger register hole and make sure plunger is being withdrawn enough to be lowered to reverse position.

[Andrew CrowParticipant @andrewcrow91475]

I can only reiterate what Bernard has said about cleaning, especially the gear teeth. Get an old tooth brush and spray the gears with WD40 or similar and give the teeth a clean. If necessary remove the tumbler assembly so it can be cleaned more thoroughly, on re-assembly lubricate with a drop of light oil.

Andy

[Charles LamontParticipant @charleslamont71117]

I agree with Bernard and Andy. For cleaning I would go for a bath of paraffin and a toothbrush. Use oil, not grease. Very unlikely, but is the plunger bent? Is the hollow grub screw that retains the plunger coming loose?

[noel shelleyParticipant @noelshelley55608]

If it used to work but now does not something has changed ! Muck in the gears = need cleaning. Muck in the plunger hole = needs cleaning. Bent or damaged plunger = repair as need be. Has the acorn knob screwed on to far ? Are the tumbler gears in their correct places,their different sizes ? It will be something simple. Study how it operates and it will hopefully be obvious.  Good luck.   Noel.

[peak4Participant @peak4]

Does Tumbler Reverse Stud (38) have an eccentric section to vary the engagement?

Locked in place by stud 40

Bill

[Neil WyattModerator @neilwyatt]

Is it possible the 28T and 30T should be swapped over?

Edit: A look online suggests they are the right way around.

This is the sort of thing that usually requires a close look at the problem, but is often a Doh! moment when you realise what’s wrong.

Neil.

[Clive FosterParticipant @clivefoster55965]

Julian

Could it be banjo adjustment.

The drop train gears look to be rather tightly meshed. tweeting the banjo down and opening up the mesh on the gears might make just enough room for the tumbler lever to reach its detent.

Try setting the gears and banjo with the tumbler in reverse.

Clive

[ChrisLHParticipant @chrislh]

The original Myford tumbler gears are made from a grade of Tufnol synthetic material. The gears that you have look to be made from metal, the small slot headed screw in the end of the tumbler shaft is not original (which is hex) and the 24 tooth gear engaging with the rest of the train has a decidedly square, un-involute appearance. It all looks as if the original set up has worn out or suffered a bad failure and has been repaired with home made parts. In that case cutting teeth with incorrect cutters to non standard depths and blank diameters would give the effects you are suffering. Straightforward cure is to obtain genuine spare parts. All rubbish of course if it has only just started happening !

[julianjParticipant @julianj]

Firstly, thank you all for taking the time to share your knowledge, this is my first post on this wonderful forum & I’m bowled over by all your helpful postings.

I should add, I’ve had this issue with the lathe ever since I purchased it 20 odd years ago!

Since my first post, I have removed the lever and change wheels, cleaned/inspected everything thoroughly. The plunger is not bent & neither is the lever shaft.

The tumbler gears are Tufnol. (thanks ChrisLH)

The lever shaft does not have an eccentric section. (thanks Peak4) When I read your post I was really hopeful this would be the case, but alas no…..

Interestingly, I tried swapping over the Tumbler gears. With the gears swapped to the wrong position, the reverse lever detent would correctly lock in place and the tumbler gears would correctly mesh with the 30 tooth headstock gear H37. However with the tumbler gears the wrong way around, both tumbler gears would mesh with the sleeve gear assembly causing the gears to lock against each other.

I should also add, with the tumbler gears in their correct locations, & with the lever locked in the top indent, the mesh between the tumbler gear and the headstock gear is very loose, and if I release the detent I can lift the lever another 1/4” resulting in a perfect mesh.

It’s almost as if the three detent holes in the headstock casting are drilled 1/4” too low.

To my eyes, the only fix would be either an eccentric reverse lever stud (38), or a modified lever casting, neither of which seems feasible….

Is it possible the wrong lever has been fitted at some point? I note the levers are still available new from Myford.

I’ve enclosed some more photos for your consideration.

Thank you all for your continued support.

 

Kind regards

Julian

[Neil WyattModerator @neilwyatt]

It’s almost as if the three detent holes in the headstock casting are drilled 1/4” too low.

Which is quite feasible!

Personally, given how you describe it, I’d fill the existing detents with epoxy steel putty, then use the lever with the detent taken out as a guide bush to drill detents in the right places for the gears you have.

Taking a couple of photos and writing a few words about it and sending them to me as a short article, while you are at it!

Neil

 

[John PurdyParticipant @johnpurdy78347]

Julian

Just out of curiosity measure the diameter of the two tumbler gears over the teeth. They should be 1.600 and 1.500, at least that is what they are on my lathe and the lever engages normally.

John

[julianjParticipant @julianj]

Hi John,

 

Thanks, yes, I’ve measured the diameter of the tumbler gears at 1.5″ & 1.6″ respectively +/- 0.010″….

I’m completely flummoxed by this issue !

 

Cheers!

Julian

[Neil Wyatt]

On Neil Wyatt Said:

It’s almost as if the three detent holes in the headstock casting are drilled 1/4” too low.

Which is quite feasible!

Personally, given how you describe it, I’d fill the existing detents with epoxy steel putty, then use the lever with the detent taken out as a guide bush to drill detents in the right places for the gears you have.

Taking a couple of photos and writing a few words about it and sending them to me as a short article, while you are at it!

Neil

 

Thanks Neil,

Well, yes, it’s a consideration… might be more feasible to modify the lever instead….

Cheers,

Julian

[Clock polisherParticipant @clockpolisher]

Good evening Julian,

I keep going back to your photos and can’t get away from the fact that the tumbler gears are two different sizes. One is a 28 tooth and the other is a 30 tooth.

I don’t have much experience with lathes but both the gears on my ML10 are identical 28 tooth.

Just a thought.

regards,

David

 

[bernard towersParticipant @bernardtowers37738]

We’ve got to be missing something as the lathe cannot have survived this long without the ability to select reverse travel and according to the spares list the tufnol gears are correct(unlikely to be wrong as they are a press fit job)

[Andrew CrowParticipant @andrewcrow91475]

I also had the same thought as Clockmaker, but I have just checked my S7 manual and the gears are correct as shown.

Is it possible that at some time the lever has been changed for one maybe from another Myford model eg ML10.

Do you know anyone else with a Super seven that you could check it against?

Andy.

[duncan webster 1Participant @duncanwebster1]

The 28/30 might be an attempt at hunting tooth so you don’t get the same pair of teeth coming together every time. As they are both idlers their tooth count doesn’t affect the ratio. The input and output gears should be the same tooth count, it might be worth checking

[Clock polisher]

On Clock polisher Said:

Good evening Julian,

I keep going back to your photos and can’t get away from the fact that the tumbler gears are two different sizes. One is a 28 tooth and the other is a 30 tooth.

I don’t have much experience with lathes but both the gears on my ML10 are identical 28 tooth.

Just a thought.

regards,

David

 

This is correct according to the manual (as has already been said). Never having needed to touch mine in the 50 years I have had the machine, I had assumed they were all 30T.

[Nigel Graham 2Participant @nigelgraham2]

My thought too, that they should be of the same diameters, probably the smaller, so examined the good books for my own Myford. I’d never even given it a thought but as John points out the lathe does use differently-sized tumbler wheels.

I have the manuals for both the ML7 and the ML7-R. These prove different wheels by 2 teeth on both machine editions; but the tooth-counts also differ between the two editions.

They are:

ML7: 20T on left, 18T on right, looking onto the end as in your photos.

ML7-R 30T left, 28T right.

So the two wheels on your lathe seem the right way round: the larger by 2 teeth on the left.

Also, at that rate, the Super 7 uses the same tumbler reverse as the 7-R.

So a replacement lever? One for another Myford “number”?

 

 

Modifying other parts and drilling new holes is too drastic. Given that your lathe has suffered with this since you bought it, I had wondered if a previous owner has either fitted wrong-size replacement wheels or has fitted the right ones for the lathe but the wrong way round. It seems you have investigated these and been able to discount them.

So to Julian’s idea: wrong replacement lever. Does it show a part-number? None is visible in any of the photos above but there may be one hidden by the other components.

 

Contact Myfords – as I did only yesterday with a query about the spindle nose thread, eliciting a helpful reply quite quickly.

=====

 

[For the record, I want to make a nose adaptor to hold my much smaller EW lathe’s 4-jaw chuck on the ML7, but the Myford thread is not standard BSW or BSF. The helpful Myfords chap said it’s of Whitworth form but the only standard match for its 1.125 X 12tpi is UNF. The Tracy Tools chap told me they have sold quite a lot of that size UNF taps and dies, precisely for making Myford tooling!

Why the little chuck on the big lathe? ‘Cos the galumphing great big Myford 4-jaw, so heavy and bulky it would be better on the Harrison L5 lathe, can’t close down enough.

Use the EW chuck on the EW lathe? Ideally, yes, but the EW’s headstock is badly worn, yet to be refurbished, and I don’t want to risk more damage by the intended task’s interrupted-cut turning.

Buy a Myford back-plate for the chuck? I don’t want to separate chucks from their beloved back-plates.

Errr… Myford plate and a small chuck dedicated to that? To use what I already have… though buying the taps and die might be not much cheaper an option.]

[Grindstone CowboyParticipant @grindstonecowboy]

The lever is an interference fit on the pivot shaft – it’ll have got moved round at some point by accident. Just needs pressing off and putting back in the correct position (probably easier said than done, I know).

Rob

[Grindstone Cowboy]

On Grindstone Cowboy Said:

The lever is an interference fit on the pivot shaft – it’ll have got moved round at some point by accident. Just needs pressing off and putting back in the correct position (probably easier said than done, I know).

Rob

I had a look at mine earlier; pre-widebed S7
Without pressing out the pivot shaft, it does appear that all the rings on it are concentric.

Bill

[peak4]

On peak4 Said:

On Grindstone Cowboy Said:

The lever is an interference fit on the pivot shaft – it’ll have got moved round at some point by accident. Just needs pressing off and putting back in the correct position (probably easier said than done, I know).

Rob

I had a look at mine earlier; pre-widebed S7
Without pressing out the pivot shaft, it does appear that all the rings on it are concentric.

Bill

Ah, okay – back to square one 🙂

[John PurdyParticipant @johnpurdy78347]

Julian

I have taken the tumbler unit off my lathe and mounted it on the milling machine to take some measurments of the spacing of the various parts. I centred the 5/8″ dia pivot under the spindle and orientated it so the centre of the dedent pin was on the same line as the centre of the pivot pin. The readings were by eyeballing the centre of the gear pivot pins so may be +- a little, but should give you an indication of if perhaps the the lever has been changed at some point.

John

[John PurdyParticipant @johnpurdy78347]

Julian

Here is another dim. you might check. On my lathe, 1976 S7B, the distance from the bottom of the front lathe shear over the top of a 17/64″ drill shank in the top dedent hole (it’s a nice snug fit) is 2.740″.

John

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