Myford Super-7 Back Gear Locked?

This topic has 11 replies, 7 voices, and was last updated 13 January 2017 at 10:13 by Robbo.

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12 January 2017 at 15:56 #277333
Oliver Webster
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@oliverwebster17169
So I have an old Myford Super 7 and for the first time I've come to turn some large-ish diameter Stainless Steel (303) so I have need of the lower spindle speeds. However, when I engage the back gears it just completely locks the spindle.

I know that I have to rotate the small key whatsit fhrough 180° which then correctly disengages the cluster. I also do not think that the back gear (the one attached to the lever) is siezed as when it's in the disengaged position (plunger lever downwards) the gear freely rotates. As soon as I move the lever up to engage it everything locks up bar a small amount of backlash. Has anyone had this before?

I get the sense I might be missing something obvious. The lathe used to belong to my grandfather and I spoke with him last night who confirmed he had this same problem before but couldn't recall how he fixed it.
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12 January 2017 at 15:56 #18363
Oliver Webster
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@oliverwebster17169
Myford Super-7 Back Gear Locked?
12 January 2017 at 18:22 #277361
Brian Oldford
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@brianoldford70365
Could the 4 step pulley and gear assembly be seized onto the spindle? If it is, and I hope not, you may be in for a tough time.
12 January 2017 at 19:05 #277371
John Purdy
Participant
@johnpurdy78347
Oliver try this. With the back gear disengaged (lever down), rotate the half moon key to disengage the bull wheel from the 4 step pulley, you should then be able to hold the pulley with one hand and rotate the bull wheel and the spindle freely. Then if you hold the bull wheel stationary you should be able to rotate pulley freely. This will confirm if the pulley is seized on the spindle or not.

John
12 January 2017 at 19:09 #277374
Oliver Webster
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@oliverwebster17169
Okay tried the above. With the half moon key flicked over and the back gear disengaged (lever downwards) everything moves independently. As soon as the back gear is brought into play (move lever upwards) everything locks solid…
12 January 2017 at 19:37 #277379
Dusty
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@dusty
In the above circumstances what are you trying to move? The only way you will move anything is by way of the belt. If you are trying to turn the chuck you will not stand a snowball in hells chance.
12 January 2017 at 19:54 #277384
Oliver Webster
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@oliverwebster17169
Indirectly I’ve tried both… Just now I was manually trying to move the chuck but when I first tried to engage (using essentially the same procedure) I just switched the motor on and the belt just slipped. Surely as it’s a lower ratio it ought to be possible to move the chuck with it engaged?
12 January 2017 at 20:04 #277388
Robbo
Participant
@robbo
Oliver

Quick thought, is the back gear engaging too tightly with the bull wheel? Disengage the bull gear from the cluster and gradually engage the backgear whilst turning the pulley cluster (take tension of belt to make this easier) and see if the bullwheel turns as the gears engage but seizes up when the lever is in its socket.

If so you need to adjust the engagement by adjusting the lever on the eccentric.
12 January 2017 at 20:06 #277389
Nigel Bennett
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@nigelbennett69913
Can you rotate the back gear shaft when it's disengaed – the one below the main spindle? If that's seized on its shaft it could be the problem. It should rotate easily.
12 January 2017 at 20:09 #277390
Simon Williams 3
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@simonwilliams3
The back gear is underneath the main spindle, and if it hasn't been used in living memory there will be a certain amount of crud accumulated on it, just 'cos it's the bit underneath.

If the bull wheel chuck and spindle turn freely separate from the pulley (with the half moon key disengaged), and the pulley itself swizzles round freely on the spindle, then the input and output to the back gear are OK, but is the back gear seized on its shaft?

Suggest you disengage the half moon key, and see if you can turn the backgear shaft underneath the spindle without operating the back gear lever to mesh it with the bull wheel..

If so then the back gear isn't seized, so I guess you're looking for a lump of something lodged in the teeth of the gears just jamming up the mechanism.

I suppose the back gear, which is mounted on an eccentric so the knob/lever behind the chuck lifts it into engagement with the driver gear (pulley driven) and the bull wheel attached to the chuck, is actually moving the right distance?

HTH Simon

edit – Nigel beat me to it….edit

Edited By Simon Williams 3 on 12/01/2017 20:10:47
12 January 2017 at 20:10 #277391
Oliver Webster
Participant
@oliverwebster17169
Looks like Robbo has hit the nail on the head. Went and pulled the belt by hand and engaged the gears and it seems to work before getting tight as the plunger engages. It must be so close as the lever isn’t overly difficult to engage but is enough I guess to lock it up. I’ve got the manual so looks like I’ll be messing about with wooden wedges tonight. Thanks for the suggestions everybody.
13 January 2017 at 10:13 #277492
Robbo
Participant
@robbo
The plunger body is held on to the eccentric by two very small grub screws underneath, which are difficult to get at.

Being of Grandfather age I am always cautious about overtightening these tichy things and breaking the hex socket, which would mean headstock off to rectify; your Grandad was probably the same so the plunger has been able to move round the eccentric.
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