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Myford Ml7 Spindle Lock

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MozamPete

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#1
As part of an upcoming mid-life refurbishment I am planning for my ML7, I would like to add some facility to lock the spindle when removing the chuck (screwed on chuck). The later Myford Super 7 had a pulley lock assembly, basically pin which would engage with the hole on the large end of the spindle step pulley and stop the spindle from rotating while removing the chuck, but the ML7 doesn't have this facility.

Everyone warns against using the backgear to lock the spindle and the only other method I have seen mentioned involved squeezing the V-belt between the countershaft and the spindle pulley together to stop it rotating - but I have a Tri-Leva so don't have the usual ready access to the belts.

The other possibility is to used a manual handle (expanding type that fits into the rear end of the spindle bore), but then you still need some way to stop that rotating as it would be hard to hold it steady and be removing the chuck with one hand at the other end of the spindle at the same time.

Some way of locking the spindle as directly as possible would appear to be best to avoid any stress on the rest of he drive train.

Any suggestions? How do other ML7 owners lock their spindle to remove the chuck? How do other lathe manufactures implement a spindle lock?
 

Randall Marx

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#2
I believe, along with many others, that under normal chuck removal circumstances, using the back gears to lock the spindle should pose no threat. The normal torque required to loosen a chuck such as inserting the cuck key and pulling it toward you, provided you don't need an exceptional pull or a hammer, mallet, etc., is not what generally damages the gear teeth. If, for some reason, you have to resort to other means to remove a stuck chuck (like very large torque or an impact torque like hitting a lever to loosen the chuck) then I would definitely encourage other means for holding the spindle.
I am interested in this subject, though, as I always dread having the chuck stick even though I oil threads and such every time it is installed. My Atlas/Craftsman lathe has an index pin that engages the bull gear, but I think that will hold less torque than the back gears.
 

aaronjb

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#3
I fully envisage a fight getting the chucks off mine lathes when it comes time to restore them (aka when I manage to dig my way back to that corner of the workshop again), I found this video detailing at least one method for doing so using a simple strap wrench:


Not quite as convenient as a locking pin or pawl, admittedly, but good for getting out of a bind I reckon.
 

MozamPete

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#4
That looks like a good method, minimal risk of damage - In my situation the problem is the lathe is a tri-leva so I don't have the easy opening cover to get to the spindle/pulleys. But that being said I haven't yet come up with a better solution so maybe the modification I should look at is to make the access to the pulleys easier.
 

aaronjb

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#5
Ah, good point.. I'd forgotten what the Tri-leva cover looked like.

I just looked it up, though, and I notice it was advertised as having "friction hold" as well as freewheel .. what happens if you engage all three levers at the same time? The differing drive speeds it would try to simultaneously achieve, I would have thought, would effectively lock the spindle up?
 
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