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Myford Super 7 Lead Screw Not Turning

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Bill Ball07/04/2020 22:54:33
3 forum posts

Hello there.

My 1982 vintage Myford Super 7 with USA Norton gear box is displaying abnormal behavior.

The leadscrew has ceased to turn under power, making fine feeds and threading most difficult. Some stime ago, in a moment of abject carelessness, I allowed the carriage to move toward the headstock under power, and the leadscrew guard (Part # A9196) bent. As the job at hand was complete, I ordered a replacement leadscrew guard and thought no more of the interaction.

Now it seems something has sheared or broken, such that the leadscrew no longer turns under power. In the lengthy history of Myford lathes, I may not be the only operator to display such carelessness.

Might anyone have a perspective on which part may require replacement to correct this condition? I am reluctant to begin to dismantle the geabox assembly without having potential replacement parts at hand, as I am on the western side of the Atlantic Ocean, and most Myford spares are thousands of kilometers to the east.

Thanks in advance for your hopefully forthcoming expert advice,

Bill

David George 108/04/2020 07:55:46
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1197 forum posts
409 photos

Have s look at the Myford web site as it gives an exploded drawing as well as a parts list. Looking at it there is a taper pin on the drive shaft which could be the weakest link. Can you try and rotate the input shaft with the drive gear disconnected to see where the disconect could be.

David

bricky08/04/2020 09:12:50
419 forum posts
48 photos

Bill I did the same thing and I suspect that you have damaged your half nuts, and that they will need replacing.I was lucky in that a gentleman on this site sold me some new spare nuts that he had.I had had a problem with banding on my work and when I had it serviced they couldn't give me an explanation as to why this was happening.When I replaced the half nuts the banding dissapeared ,so turners that are haveing this problem might have half nuts that want cleaning or replaceing.

Frank

Steamer191508/04/2020 09:54:51
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162 forum posts
41 photos

Bill,

Are all the teeth still on the tufnol tumbler reverse gears. Just a thought...

Best regards,

Steve.

Howard Lewis08/04/2020 12:46:44
3160 forum posts
2 photos

Suggest that you begin to trace the drive from the spindle, towards the Leadscrew, until you find the gear lacking teeth, or sheared pin or key.

Lets hope that the damage is not too serious and can be repaired easily and economically.

Keep, us posted as to what you find.

There will be others with similar problems in the future who can benefit.

Plus it will add to our general store of knowledge, which may be useful elsewhere.

Howard

Bill Ball08/04/2020 20:26:57
3 forum posts

Thanks to everyone for the helpful advice. None of the visible gears are stripped or broken.

I rather suppose I should also have inquired about how to remove the gear box from the Super 7 lathe -- dissecting the internals seems like the next step.

How does one remove the gearbox so as to access the left hand end of the leadscrew?

Bill

JohnF08/04/2020 22:35:51
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969 forum posts
142 photos

Bill, have a look at this post on this site **LINK** it pretty much everything you need and there is a link on the post to the QC gearbox assembly diagram

John

Edit -- Just to note the dowels on the tailstock end leadscrew bracket are tapped to facilitate removal -- you may have to make a simple puller -- they are ?? BA I can check this for you if needs be just PM me

Edited By JohnF on 08/04/2020 22:39:27

Bill Ball11/04/2020 17:45:40
3 forum posts

Many thanks to all respondents,

Following your advice, I checked for damage, finding none. The apron would advance using the handwheel on the tailstock end of the lathe, so the half nuts were undamaged.

Before tacking gear box removal, I drained the gearbox oil, blasted the gearbox interior with aerosol brake cleaner and refilled with new Myford specification oil. Remarkably, the leadscrew behaved normally.

I conclude that a foreign object or swarf prevented the selector lever on top of the gearbox from engaging. and that was the problem.

Bill

Neil Wyatt11/04/2020 17:50:31
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Moderator
17742 forum posts
698 photos
77 articles
Posted by Bill Ball on 11/04/2020 17:45:40:

Many thanks to all respondents,

Following your advice, I checked for damage, finding none. The apron would advance using the handwheel on the tailstock end of the lathe, so the half nuts were undamaged.

Before tacking gear box removal, I drained the gearbox oil, blasted the gearbox interior with aerosol brake cleaner and refilled with new Myford specification oil. Remarkably, the leadscrew behaved normally.

I conclude that a foreign object or swarf prevented the selector lever on top of the gearbox from engaging. and that was the problem.

Bill

It's not unknown for the shear pin to break, and the broken parts catch again, if you find that next time it's under load it stops rotating, you know why...

Neil

Steviegtr11/04/2020 23:18:10
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1166 forum posts
99 photos

Another thing with the gearbox is the top lever has to be positively in the right spot. A few times I have thought mine had broke, only to give the lever a good push to get it in position. I guess straight cut gears have to be meshed . Generally there is not much in there to fail.

Steve.

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