Replacing Broken Tumbler Gear on Myford

[David HaythornthwaiteParticipant @davidhaythornthwaite90386]

I have a Myford Super 7B lathe and I am VERY distressed to have broken a tooth from the 39 tooth Tumbler gear in the Norton QC gearbox. (Don't ask it is too painful)!

At the end of a turning job that was on the limit of the Myford's capacity, there was a thump and it was found that a tooth had broken from the Tumbler gear.
The attached photo illustrates the problem of trying to remove the tumbler gear in order to replace with a new gear. The replacement gear wheel is apparently available from Myford, but I cannot see how they could have assembled it in the first place, nor can I dismantle it.

The photo shows the Input shaft of the gearbox withdrawn from the Input shaft housing in order to show the spline on the input shaft which normally runs in the input shaft housing. The Tumbler gear normally protrudes through a slot in the input shaft housing to engage with the spline in the input shaft.

The selector, which is a casting, slides on the input shaft housing to enable the tumbler gear to engage with one of the nine gears for the various ratios. The bottom of the selector caries a short spindle on which the tumbler gear runs and the short spindle is held captive in the selector casting by a taper pin – according to the drawing – it is impossible to see visually.

The task appears to be to remove the input shaft housing, slide the selector off the input shaft housing and then to remove the tumbler gear. However in reality it is impossible to remove the input shaft housing as the selector will not slide off it due to the teeth of the tumbler gear protruding into the slot in the housing. Equally, it seems impossible to remove the taper pin + short spindle + tumbler gear as they are hidden at the bottom of the gearbox underneath the input shaft housing !!

I can only assume that Myford inserted the taper pin through the oil drain hole using a special tool, but extracting it would be another matter and would certainly need the gearbox upside down on the bench.

Has any reader replaced this item on their ML super 7 and can anyone advise me as to how this is possible. I am very distressed at having “broken” my treasured Myford. P L E A S E can ANYONE help me?

[David HaythornthwaiteParticipant @davidhaythornthwaite90386]

Replacing the 39 T Tumbler Gear on a Myford Super7 B

[john fletcher 1Participant @johnfletcher1]

David I've sent you a PM. John

[Brian WoodParticipant @brianwood45127]

Hello David,

I share your distress, but not the experience.

Looking at Myford's drawing, I think the trick is to first remove the indexing pin assembly for gear selection and then rotate the input shaft housing complete with the selector.

I foresee a snag in that you will probably also have to pull the layshaft, (item 159 in the drawing) to provide enough room to complete the rotation and gain access to the taper pin that holds the short spindle this gear runs on.

Hopefully John Fletcher can offer some more encouraging 'magic'

Kind regards Brian

[David HaythornthwaiteParticipant @davidhaythornthwaite90386]

Hi Brian,

Firstly I hope that you and your wife are keeping well in these difficult times. When I read your post regarding rotating the input housing complete with the the selector, it had me running into the workshop shouting "well done Brian – now why did I not think of that"

On studying the gearbox however, it transpired that this was not possible:-

Looking at the gearbox from the lathe headstock end, it is impossible to rotate the selector CLOCKWISE in a vertical plane as the horizontal sliding area where the selector locks to set the TPI, stops any movement CLOCKWISE of the selector arm. That is what it is there for.

Again, looking at the gearbox from the lathe headstock end, and trying to rotate the selector ANTICLOCKWISE in a vertical plane, it is only possible to rotate the selector anticlockwise by about 15 degrees after which the Tumbler gear, which is below the input shaft housing hits the front of the gearbox stopping further rotation.

Other than removing the taper pin using a 1" gnome who has strong muscles and can sit in the bottom of the gearbox, I am still at a loss – unless I am missing something!

Thanks for your kind input though Brian. John suggested someone else who may be able to help. I shall follow that up tomorrow.

Kind Regards

David

[speelwerkParticipant @speelwerk]

Although from a MK.1 this might help, **LINK** Niko.

Edited By speelwerk on 01/09/2020 23:55:28

[Brian WoodParticipant @brianwood45127]

Hello David,

We are well over here thank you, I hope the same applies to you both

I had overlooked that fact and I have just been through that excellent U tube video that Speedwerk posted. The key to it all is clearly the layshaft, with that removed you can see what you are doing.

Sorry to have raised your hopes, when you see the casting of the selector itself so well shown on Speedwerk's link there is obviously no room for that to rotate.

A rather similar method is needed to get the clapper box and calibrated slide off the ram end on certain shapers; that has to be rotated to align the machined clearance over the clamp screw. With that aligned the whole assembly comes off easily.

I hope you get the gearbox repaired and back in operation again very soon In the meantime stay well

Kind regards Brian

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