Myford Super 7 Tumbler reverse lever not engaging

[Graham Meek]

On Graham Meek Said:

 

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,

Indeed. The teeth on John’s gears are much “meatier”. And in Julian’s original picture, the teeth on the Tufnol gears appear much thinner than the teeth on the meshing metal gears.

I think I would buy a new pair of genuine Myford Tufnol gears.

[alecsParticipant @alecs]

Oops. Forgot Julian’s pic of the perhaps errant fibre gears in his first post.

[Speedy Builder5Participant @speedybuilder5]

Julian, in your photo of the three detention holes, Why is there a mark on the lower hole where presumably the detent pin should go (but doesn’t engage).  Is there a possibility that at some time ago, the lower detention hole was plugged and re-positioned ?

 

[ChrisLHParticipant @chrislh]

Just to add another clue to the mystery I have made caliper measurements across engaged pairs of 30 tooth and 28 tooth tumblers and the 30 tooth lathe spindle gear on my old but hopefully healthy Super 7. I know that the OD’s of your Tufnol tumblers check out OK at 1.5 and 1.6 but the above measurements should tell you if the teeth on your tumblers and your 30 tooth lathe spindle gear are cut to something like standard form..

Caliper measurement 30/30      3.096 (theoretical nominal 3.100) plunger engaged, 2.980 tight mesh

Caliper measurement 30/28      3.003 (theoretical nominal 3.000) plunger engaged, 3.074 tight mesh

My idle curiosity, how did you manage to detach the tumblers from the lever ? On my lever there seems to be some sort of rivet arrangement in each gear spindle with no obvious way of disassembling.

[ChrisLHParticipant @chrislh]

Apologies. my tight mesh measurements are the wrong way round. Correctly ….

Caliper measurement 30/30 3.096 (theoretical nominal 3.100) plunger engaged, 3.074 tight mesh

Caliper measurement 30/28 3.003 (theoretical nominal 3.000) plunger engaged, 2.980 tight mesh

[John PurdyParticipant @johnpurdy78347]

Chris
When I replaced the tumbler gears with broken teeth on my lathe, due to stupidity on my part (the wrong gear in the gear train resulting in the gear train locked up and not checking before engaging the clutch!) I just pressed the two 7/16″ pivot pins out of the casting. The protrusions that you think look like rivets appeared to me to be machined on the ends of the pivot pins, why? I have no idea. Maybe someone else here can comment on that?
Out of curiosity I checked your measurements on my lathe and they are essentially the same as yours:
With the dedent engaged: 28/30 2.999″ and 30/30 3.104″
John

[John Purdy]

On John Purdy Said:

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

John,

I am deeply indebted to you Sir… You’ve given me the solution !

 

Having looked at your photo & stewed on it for a couple of days, I re-measured the distance on my lathe as per your photo & my location holes are a good 1/4 inch lower than yours (standard?). The enclosed photo shows my calipers set at 2.740″. The photo isn’t really clear & it’s a little tricky to measure with the gear cover in place (I notice yours is removed in your photo) but…. there lies the problem !

I’ll be on the phone to Myford first thing in the morning to order new set of holes.

It’ll take me a little while, but I’m thinking of a couple of engineering solutions & will report back in due course!

My most sincere thanks to everyone that has contributed on this thread, you’ve all helped me more than you will ever know, I’m humbled by your generosity of knowledge.

Kindest regards to all,

Julian

[John PurdyParticipant @johnpurdy78347]

Julian

Glad it looks like you have found the reason for your problem! If the holes were drilled using a jig as Graham Meek says he recalls in a previous post above, the only thing I can think of for the misplacement of the 3 holes is the jig moved or was not placed properly.  Doesn’t say much for Myford’s post assembly quality control. That should have been easily picked up if any even rudimentary checks were done.

John

[alecsParticipant @alecs]

Very small sample size. It might be worth measuring a couple of other S7s to confirm that measurement before performing any major surgery.

It would be worth a call to Myford –they are very helpful — to find out how this could happen. It seems unlikely that both a drill jig was used wrongly and it was missed in both assembly and final QC check.

[John PurdyParticipant @johnpurdy78347]

Sorry, I agree with Alecs, I meant to add to my post above, but forgot, that maybe some other owners of S7s could make that measurement on their lathes just to confirm that julians’ is off before he does any drastic surgery. But I don’t agree with Alecs on the point of being missed as from my experience with Myford QC the fact that it may have been missed would not surprise me at all.

John

[alecsParticipant @alecs]

As an ex-toolmaker who made a few drill jigs (long ago!) I would be somewhat surprised if that bottom surface of the headstock was used as a reference when drilling those three detent holes. The critical references are the main spindle hole and the tumbler pivot hole. The headstock base surface is irrelevant to the tumbler operation and gear mesh.

And we know from widespread experience that the exact centre height on Myfords varies slightly from one lathe to another, indicating that the bottom headstock base surface was possibly machined to whatever it took to clean up the casting. So not a fixed reference surface for a drill jig.

I would definitely call Myford and discuss before any major surgery. Just in case there is some odd variation in tumbler dimensions between models, eras or even individual machines. In the spirit of “Measure twice, cut (or drill) once”.

[John PurdyParticipant @johnpurdy78347]

Alecs
I agree with your statement that the bottom surface of the head stock is irrelevant to the meshing of the tumbler gears but it was a convenient surface to make a reference measurement from. I also agree that the centre height varies between S7 lathes, but we are talking here about ~1/4″. The centre height of my lathe measures 3.5036″, so only 3.6 thou high from nominal.

As a double check I have just jury rigged a set up to measure the distance from the top of the tumbler pivot pin to the top of the upper dedent hole in the head stock casting.
As can be seen in the pics below I have rested a 3/8 x 3/4 parallel on the upside down tumbler pivot pin, held it in place by a magnet and set it level to 0.0 degrees using a small digital level. I then compared the level of the top of the drill shank in the upper dedent hole to various gauge blocks sitting on top of the parallel. The top of the .950″ block ended up coincident with the top of the drill shank as close as can be judged by eye. So the distance from the top of the tumbler pivot pin to the top of the upper dedent hole measures 1.325″ (.375+.950) and I would guesstimate to +-10 thou or less.

Justin,  could you maybe make a similar measurement and see how yours compares with my measurement? This would eliminate the problem of using the bottom of the head stock as a reference to determine if the dedent holes are positioned correctly.
John

[noel shelleyParticipant @noelshelley55608]

I have followed this thread with great interest ! I find that the solution is that the holes are in the wrong place hard to accept ? The state of the 2 tumbler gears is where my money is ! Or that following a serious crash something is bent. The 2 little “rivets” on the ends of the tumbler wheel shafts are from memory a means to oil the running surface of the tumbler wheels. I would be loathe to drill new holes as the error is less than a hole out and could go wrong . Noel.

PS I have 3 S7s, 2 in bits ! A while back I asked where abouts Julian is, have I missed his answer ? If he is with in a reasonable distance of me I would be happy to try a spare assembly on his machine to try and resolve this. The witness marks on the machine indicate it has NOT always been like this ?  N

[Graham MeekParticipant @grahammeek88282]

At some point this machine left the factory and I cannot believe that it left the factory with a non-functioning Tumbler Reverse mechanism. From its colouring it is clearly an early machine, not one of the last just slapped together.

I also cannot believe that this machine has made it throughout its life with only one set of Tufnol gears. They used to get broken with great regularity in the Metalwork classes at school.

The OP has not as yet established whether these gears are the correct ones, or someone’s attempt at gear making / cost cutting.

I gave the simplest of checks to see if the gears are correct but this seems to have been totally missed and it would point straight to the problem.

Instead there is an obsession that the Tumbler location holes are in the wrong place. It is clear from the markings around the Tumbler dentent holes that the machine has been used without the pin engaged.

From the last post by the OP he is going to get some “New Holes” from Myford, quite what the staff at Myford made of that I do not know.

Regards

Gray,

 

[Dave HalfordParticipant @davehalford22513]

The other possible reason for the miss match being parts swapping. Over recent years there have been a lot of Myfords broken for parts posted on Ebay so the likelyhood of a ‘bitza’ is quite possible.

 

I don’t understand the reluctance of the OP to ring Myford and ask rather than continuing to fixate on holes drilled wrong on day one more than 50 years ago. Admittedly it’s easy to understand hole positions, but also easy to drop a lathe while staggering down the back garden path from the shed before loading it into a van with an oops I’ll have to get another lever off Ebay.

[Phil super7Participant @philsuper7]

looking at the pictures i noticed the change gear backplate has a crack, indicating a hard life or some form of impact.

The tumblers gears 30T & 28T need replacing. Regarding the Tumbler reverse lever check for damage, has it been repaired, misplacing the gear stud holes.

I use to visit myford on a regular basis and in deed the fitters used a jig for drilling the three holes.

[John PurdyParticipant @johnpurdy78347]

Julian, I apologize, I don’t know where “Justin” came from. All I can think is that it was 11:30 at night and my cat was on my lap trying to climb onto the keyboard!

I agree with all of the above comments, all I am trying to do is provide a means of determining if the dedent holes are correct so Julian can eliminate one possible source of error. I also consider the gears themselves to be most likely the problem.
John

[Nigel Graham 2Participant @nigelgraham2]

Indeed.

Consider ye not any drilling etc. AT ALL until all other possibilities have been exhausted, and in this case they are:

– Replacement gears of the right nominal diameter and teeth-counts but poor tooth form (not original Myford gears but rather badly machined copies, throwing the centering out);

– Replacement tumbler lever and perhaps other parts, that are incorrect for the lathe pattern.

 

Do you know anyone else sensibly near you, who can try his Myford Super 7 tumbler components on your machine- and vice-versa?

If his work on your lathe but yours gives the same error on his, then clearly the components on your lathe are wrong in some way – not the lathe itself.

You can also of course measure the pitches of the holes on the two lathes: they should be identical to very close limits, allowing for some wear.

 

Others have pointed to measuring the height of the holes from the underside of the shear, being potentially fallacious. To overcome that, measure as you did, then subtract the shear thickness, to give the height from the underside of the headstock. However, that still does not help if the spindle height is not close to nominal, though that is measureable too. It is the geometry of the moving parts and the detent holes with respect to each other that matters, not the spindle height.

[Swarf MakerParticipant @swarfmaker85383]

I think that I would be looking at the root diameter of the 30T idler as a potential source of the problem. If the root diameter is too large then it will restrict how deeply the teeth of the mating gears can engage.

The geometry dictates that a very small restriction to the movement of the gear along its arc is leveraged to a significant change in position of the lever at the point where it is intended to lock.

[Swarf Maker]

On Swarf Maker Said:

I think that I would be looking at the root diameter of the 30T idler as a potential source of the problem. If the root diameter is too large then it will restrict how deeply the teeth of the mating gears can engage.

The geometry dictates that a very small restriction to t

 

The movement of the gear along its arc is leveraged to a significant change in position of the lever at the point where it is intended to lock.

Both those fibre gears look like they were made by Blind Freddy, using his trained rats. The tooth profile is visibly all wrong. And the teeth are very thin near the tip. Obviously going to need replacing soon. I’d be investing in a new pair before attacking my lathe bed with a pistol drill.

 

[Swarf MakerParticipant @swarfmaker85383]

I have an S7 in excellent condition and my ‘Tufnol’ gears are fully formed and unworn. There is next to no backlash between the gears in either locked position.

To prove my point regarding root diameter of the 30T gear, 4 thicknesses of copy paper inserted between the spindle gear and the 30T idler, reproduced the issue very clearly.  The lock could not be engaged by quite some distance.

[oilcanParticipant @oilcan]

If the OP has access too, or knows someone with a 3D printer, it might be worth printing off a couple of gears. i believe Thingyverse has files for Myford tumbler gears in 30T & 28T. When I, through operator error, damaged the 30T tufnol gear I couldn’t find replacement tufnol gears for love nor money. printed one off in ABS and it’s lasted so far (18 months). I did need to clean up the bore with a 7/16 reamer to get it to slide on the stub shaft.
it does seem to be a puzzle. I can’t see something as badly positioned holes slipping through QC. The tumbler arm must be correct otherwise you couldn’t get the two gears on. The gears do not look propriety ones, or even correctly made. if the pitch diameter of one is oversize, and the corresponding gear is made with an undersize pitch diameter to fit, (they do look decidedly home made) they would still mesh together, but would it affect how they mesh with the spindle? or have i been drinking too much Timothy Taylor Landlord again?

[Robert Atkinson 2Participant @robertatkinson2]

While I’m strongly in the “tumbler gears are incorrect” camp is there any chance that the gear on the back of the spindle is wrong? A lot less likely but still needs to be checked.

Robert.

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