Myford Super 7 Tumbler reverse lever not engaging

[JasonBModerator @jasonb]

To me the gear teeths narrower than the other teeth and narrower than John’s, could they be homemade replacements that are a bit off.

If there is another 30T in the gear train take them both off and compare, particularly the diameter across the root of opposite gaps.

 

[duncan webster 1]

On duncan webster 1 Said:

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

The 30T is an idler when the lever is up. However when the lever is up the 30T drives the 28T so I would have thought you get a small difference in ratio

[Adrian R2Participant @adrianr2]

Press out the pivot shaft (38) and make an eccentric replacement with a slight offset?

Once reassembled no-one would ever notice.

[Martin of WickParticipant @martinofwick]

Given the tumbler gears are all correct and the lever is not distorted, if distance from front shear to lower detent checks out correctly and the headstock spindle gear truly has 30 teeth, then it is a genuine mystery!

Clutching at straws, it might be worth checking the plunger mechanism in case something is pushing the pin off centre slightly. Only say this because I sometimes have a bit of trouble engaging the lower detent that usually requires a bit of ‘twiddling’ of the detent pin to fully engage while holding the lever down, but it is not as far out as 1/4 inch!

Perhaps you could ‘borrow’ an S7 reversing lever and see if that improves matters.

If te detents ae actually in the wrong position, then fill and drill as previously suggested.

 

[John Purdy]

On John Purdy Said:

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,

Thank you so much for taking the time to share the dimensions. I borrowed your technique (I’m learning so much from this forum!) & measured my lever in comparison to your drawing. My dimensions are in red & look to be very similar apart from the distance from the end of the plunger and also the offset of the bottom left tumbler gear shaft…..

[John Purdy]

On John Purdy Said:

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

Thanks once again John,

Apologies but I’m a little unsure exactly where the ‘bottom of the front lathe shear’ is. I’ve enclosed some further photos but it’s quite hard to see in the images….

[julianjParticipant @julianj]

Thank you all for taking the time to help me out, I’m bowled over by the generosity of the forum members.

I’ve enclosed an image of the location holes & the witness marks made by the plunger demonstrate the issue.

I’m resigning myself to either ‘just living with it’ or possibly modifying the lever in some way…

[JasonBModerator @jasonb]

Plotting the red dimensions in CAD there is very little difference between the pivot point and the PCDs that will mesh with the gear below so I doubt the 4thou would account for your problems unless as I said the gear has not been cut correctly

[noel shelleyParticipant @noelshelley55608]

Ah ! That’s interesting, the witness marks on the headstock. I wonder whether when the lathe was delivered to Julian it was clouted, bending the lever ? Where abouts are you Julian ?    Noel.

[Robert Atkinson 2Participant @robertatkinson2]

Could someone have fitted the lever from a ML7? As this uses smaller gears it could fit the fault.

Robert.

 

[duncan webster 1Participant @duncanwebster1]

In one direction the 30 is an idler between in and out, in the other both 30 and 28 are idlers. The overall ratio in to out is not changed.

[julianj]

On julianj Said:

I’m resigning myself to either ‘just living with it’ or possibly modifying the lever in some way…

I think I would fix a thin strip of stainless steel over the three holes and make three holes in the strip at the appropriate locations. If necesary, the existing holes in the casting could be elongated to allow the plunger to engage to adequate depth.

[duncan webster 1]

On duncan webster 1 Said:

In one direction the 30 is an idler between in and out, in the other both 30 and 28 are idlers. The overall ratio in to out is not changed.

Sorry it was too early for me.

[Dave HalfordParticipant @davehalford22513]

Ring or visit Myford either in Mytholmroyd or one of the shows, they still refurb old machines. The lever may have a stamped part # under the paint.

[Graham MeekParticipant @grahammeek88282]

From my days designing the Screwcutting clutch for this lathe I would like to make a few observations.

The central shaft which the tumbler reverse pivots on is ground concentric throughout, ie there is no eccentric portion.

The tumbler gears look as though they are the wrong tooth form. Judging by damage to the teeth on the sides of each gear.

The outside diameter might be correct but if the tooth form is not correct the gears will not engage properly. The Gear on the Lathe Spindle could well be running on the bottom of the Tufnol gears tooth form.

To check these gears are correct. Measure across 4 gear teeth with a vernier callipers then measure across 3 gear teeth. Take the smaller dimension from the larger. The reading should be 0.1476″ which is the base pitch for 20 DP 20 degree Pressure Angle, (PA). (Or pi x Cos PA/DP).

From the photographs they do not look deep enough to me.

From memory when visiting Myford’s at Beeston, the holes in the Headstock were drilled using a drill jig so I doubt these would be wrong.

Regards

Gray.

 

[peak4Participant @peak4]

Peter, If you have access to Facebook, there’s a chap who was selling the gears @ £25 a pair, though inflation may have put the price up a bit. Nominally half Myford price

https://www.facebook.com/groups/917590484920210/posts/6172753329403873

Bill

[John PurdyParticipant @johnpurdy78347]

Julian

This is how I measured the 2.740″ distance from the bottom of the front bed shear to the top of the 17/64″ drill shank.

John

[julianj]

On julianj Said:

Thank you all for your continued support.

I

 

Kind regards

Julian

Above and slightly to the right of the bolt the is holding outer gearbox cover is a line. Is this a casting mark or is it a crack? If the latter, is it poossible that that the entire geabox cover has been pushed upward and is now fouling the tumbler gear lever?

[ChrisLHParticipant @chrislh]

It looks as if the Tumbler Reverse Lever travel between correct meshing in forward and reverse could be OK – it’s just that the lever doesn’t engage in the holes.

If this is the case then it would point to the lever locking pin being in the wrong position in the Tumbler Reverse Lever. Maybe this corresponds to the item intended for the ML7 Connoisseur which lists a different part number for this item  (73/1208) from that for the Super 7 (A1948/1). Frustratingly I have been unable to check that the Connoisseur uses the 28/30 tumbler gear combination. Somebody confirm or otherwise ?

[Nigel Graham 2Participant @nigelgraham2]

Really, the best bet here is to find what is any part-number is marked on the lever and the tumbler-gear cluster, and ask Myfords! May be an idea to note the lathe’s serial number, too.

Examining the various replies and the photos I suspect more and more that a previous owner has fitted Myford replacement parts but the wrong ones for this version.

The detent can’t be in the wrong position in the lever, but the lever might be the wrong one for the Super-7!

The lever and tumbler frame will be Myford but might the gears be non-Myford? I don’t know if that would make a difference.

[ChrisLH]

On ChrisLH Said:

It looks as if the Tumbler Reverse Lever travel between correct meshing in forward and reverse could be OK – it’s just that the lever doesn’t engage in the holes.

If this is the case then it would point to the lever locking pin being in the wrong position in the Tumbler Reverse Lever. Maybe this corresponds to the item intended for the ML7 Connoisseur which lists a different part number for this item  (73/1208) from that for the Super 7 (A1948/1). Frustratingly I have been unable to check that the Connoisseur uses the 28/30 tumbler gear combination. Somebody confirm or otherwise ?

That is quite possible. The Connoiseur has the tumbler reverse pivot 11mm lower due to the larger big bore spindle, according to Graham Meek’s article on his dog clutch for the Connie.

The Connie tumbler lever could have the same geometry for the pivot spindle and the two gear spindles, but the locating plunger would need to sit 11mm higher than the S7’s plunger, in order to match with the standard 3 detente holes drilled in the headstock.

That might explain the different part number.

And that would be the critical dimension to measure and compare.

[Graham Meek]

On Graham Meek Said:

From my days designing the Screwcutting clutch for this lathe I would like to make a few observations.

The central shaft which the tumbler reverse pivots on is ground concentric throughout, ie there is no eccentric portion.

The tumbler gears look as though they are the wrong tooth form. Judging by damage to the teeth on the sides of each gear.

The outside diameter might be correct but if the tooth form is not correct the gears will not engage properly. The Gear on the Lathe Spindle could well be running on the bottom of the Tufnol gears tooth form.

To check these gears are correct. Measure across 4 gear teeth with a vernier callipers then measure across 3 gear teeth. Take the smaller dimension from the larger. The reading should be 0.1476″ which is the base pitch for 20 DP 20 degree Pressure Angle, (PA). (Or pi x Cos PA/DP).

From the photographs they do not look deep enough to me.

From memory when visiting Myford’s at Beeston, the holes in the Headstock were drilled using a drill jig so I doubt these would be wrong.

Regards

Gray.

 

This is the most likely culprit. Poorly made aftermarket replacement gears may have been fitted, as commonly happens after a crash breaks a few teeth etc.

The OD of the gears may be correct, but root diameter should be measured too, and is easily done. Ideally pitch diameter should be measured, using the appropriate gear measuring rods, not common in the home workshop!

While gear replacement would be the most likely action by a previous owner, the previously mentioned incorrect Connoiseur lever replacement  would be a close second. Someone pointed out earlier a crack in the inner gear casing, indicating the lathe may have suffered a fall during transport etc, which could gave also broken the original lever.

[duncan webster 1Participant @duncanwebster1]

If you consider getting replacement gears make sure they are genuine Myford. I bought some Myford clone years ago and they were well undersize. The supplier didn’t quibble when I sent them back, so I suspect this was not uncommon.

With a bit of ingenuity it should be possible to measure the arbour centres with the lever in the up and down positions, that will tell you if the lever is correct

[Graham MeekParticipant @grahammeek88282]

The case of the wrong lever does not work for me. The ML7 lever is held in place totally differently to the S7, The ML10 does not have one and the Big Bore lever is going to be longer due to this lever fulcrum point sitting lower on the headstock, but still working on a similar radius on the headstock casting.

When comparing John Purdy’s Tufnol gears in the photograph above and those on Julian machine they are nothing alike. Julian’s gears look to have been cut with an endmill by comparison. The teeth look more like the ones found in a clock.

Regards

Gray,

[Neil WyattModerator @neilwyatt]

By using a 28T and a 30T, they can both be placed so their PCDs engage the bull wheel at the same distance from the pivot without the smaller gear fouling the pivot gear. This makes the geometry a bit simpler to lay out. A 29T gear would not quite be small enough to stop the smaller gear fouling and, obviously, two 30T gears would engage the pivot gear fully and lock everything up.

Neil

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