Worm Drive Seized

Hi All,

New user here with a sticky problem that hopefully someone much wiser than me can shed some light on how I could proceed.

A few years ago I was given an old Sheraton lathe that had been sitting outside a factory under a tarp for many, many years. It was pretty rusty and seized up but after a lot of elbow grease and a bit of swearing I managed to restore it back to working order. I use it here and there as needed on projects that pop up from time to time and it has proven invaluable. Anyway, this is my lathe.



Everything worked perfectly except the apron clutch which would never engage, so last week I viewed a mrpete22's video on cleaning the apron which allowed me to fix the apron clutch and for the first time since I've owned it the apron clutch was engaging and I now had power driven longitudinal and cross-feed capabilities. Great.

Unfortunately my joy was not long lived. A few minutes into testing its operation the worm drive in the apron decided to stop rotating. Nothing else is seized. I tried to upload a video of the other component's movement but was unable to so instead I have uploaded it to YouTube and can be viewed here: https://youtu.be/lTTUGVvQdKE

I have since removed and dismantled the apron but am unable to remove the worm drive. The pin which holds the worm drive collar in place is located facing the apron casing, and as such I can't get to it, and since the worm drive is seized I can't rotate it to gain access.

Due to the pin's location it's difficult to show it in a photo but this is the best I could do.



So I seem to have come to an impasse. I'm stuck and have no idea how to proceed.

Any suggestions are most certainly welcome.

Thanks.

​See if you can't gently pry out the long key with a very small screw driver. If you can,
then you should be able to tap out whatever pin remains in the hole.
Don't forget first make a mark on the outboard side of the nut that screws onto the
worm gear. If you put it on backwards, the pin hole will never correctly align.

PMc

View attachment 334074 View attachment 334075

Is it possible that the pin sheared and the collar self tighten to lock everything in place? I imagine the gear train can exert a pretty good amount of torque.

Just a thought.

Ben

A Can of Worms

Although Chuff doesn't say exactly where the worm gear has seized,
I am guessing that the sleeve that the worm gear rides in has either rusted up or filled
with debris, or both. That apron doesn't look very clean.
There is a gear involved that rides the worm gear and it could be seized
against that gear, but I kinda doubt it. More that likely the worm gear just won't turn
anymore. I doubt pin shear also, but I guess anything is possible when it comes
to these neglected machines.

PMc

View attachment 334087

Suggestion - make a pin style hook spanner (this pair were shaped with a band saw in a few minutes) to fit pinned collar and drill a new hole with a drill to suit pin (not deep enough to drill into worm)

Maybe you can get something to move?

BDRetz said:

Is it possible that the pin sheared and the collar self tighten to lock everything in place? I imagine the gear train can exert a pretty good amount of torque.

Just a thought.

Ben

Click to expand...

Ben, you hit the nail on the head.

In mrpete22's video it clearly shows that the pin went through the collar, then the worm drive and finally through the long key in the key-way slot.

You can't see the pin in the below photo as it's facing the gear to the right of the collar, but it's clear that the pin is most certainly not aligned with the key which is clearly visible in the 11 o'clock position. Assuming pete22's video is accurate, and I have no reason to believe it's not, then indeed the pin has sheared and the collar has rotated clockwise more than 90 degrees, thereby further tightening onto the worm drive and locking it solid.



Thanks Ben. I was so certain that was the problem so I went with it.

I placed the apron in the vice and grabbed the collar with a plumbers wrench. It was tight as hell but I managed to rotate the collar. Unfortunately, the worm drive rotated with it. Having no option but to use a hammer, I rotated the collar far enough that I could get a center punch into the hole for the collar pin, and after quite a few harder & harder taps, I realized that tapping was not going to cut it, so I bit the bullet and gave the center punch an all mighty whack with the hammer and that did it.

Job Done!

Interestingly, the pin did not originally go through the collar, worm drive and key as shown in pete22's video as can be been in the photo below.



No hole in the key, just a short pin to locate the key in the key-way slot at the other end of the worm drive, not the collar end. I've closely inspected the thread on the worm drive and there is no sign of any hole in the worm drive that the pin could have sat in. As far as I can tell the pin relied purely on friction to hold the collar in place. This doesn't sound feasible or logical but there are no holes in the threaded end of the worm drive for the pin to sit in whatsoever.

The collar is a bit rougher than when I started as one would expected once deploying a center punch and hammer, but it is still most certainly serviceable. I intend reassembling the lot and will drill a hole through the collar and the worm drive and will be inserting a pin through the whole lot.

Thanks again Ben and the others who replied to this thread. Problem solved.

Chuff

BDRetz said:

Is it possible that the pin sheared and the collar self tighten to lock everything in place? I imagine the gear train can exert a pretty good amount of torque.

Just a thought.

Ben

Click to expand...

I was just thinking about that last night Ben. If the worm seized inside the collar, it must have been during an operation using the power takeoff feature. I can only imagine the torque values involved on all of the parts, all the way up through the gearbox and the side gears. With any luck, the belts slipped when this occurred without snapping parts off, especially in the apron. Could be exponentially worse if in back gear, or even a gear-head lathe!

I'm not sure if an apron part seizing (and stopping the lead-screw) is any different from say, stalling the machine with too large a cut. Wouldn't the forces be about the same on the drive train? I would think so. I know I've done that once or twice in my life.

I also noticed a very different oiling system for the worm gear in that Sheraton lathe. There is an oiling tube that directly extends to the worm gear. On the South Bends, oiling relies on a felt that wicks oil from the reservoir up to the casting (good luck with that!). That's one more good reason for felt replacement and having a reservoir full of clean oil. But I do like the direct oiling method as well. Wouldn't be a bad modification to make on these South Bends.

But I'm kind of stumped that I don't see a reservoir of any type on this apron. I see an open drain hole at the bottom on the front view, but the square "enclosure" for the worm kinda looks fabricated out of plate steel. Is that even possible? There is also a big knob at the bottom of the apron, but I don't know what that's for....maybe a clutch? I don't know enough about these lathes to say.

I'm hoping Chuff can get this machine back to good order and that he hasn't broken anything. From time to time we hear from an old grizzled machinist advising to just "slather an old machine with oil and start making' chips...it will be fine". With all due respect to Chuff, I'm afraid that's not the case here. His machine looks fairly clean, so whose to know.
Hindsight is always 20/20, huh?!

PMc

View attachment 334129

mcload said:

I was just thinking about that last night Ben. If the worm seized inside the collar, it must have been during an operation using the power takeoff feature. I can only imagine the torque values involved on all of the parts, all the way up through the gearbox and the side gears. With any luck, the belts slipped when this occurred without snapping parts off, especially in the apron. Could be exponentially worse if in back gear, or even a gear-head lathe!

Click to expand...

Luckily that's exactly what happened. No other damage whatsoever.

mcload said:

But I'm kind of stumped that I don't see a reservoir of any type on this apron. I see an open drain hole at the bottom on the front view, but the square "enclosure" for the worm kinda looks fabricated out of plate steel. Is that even possible? There is also a big knob at the bottom of the apron, but I don't know what that's for....maybe a clutch? I don't know enough about these lathes to say.

Click to expand...

In the photo below the very bottom gear (clutch gear) sits in a valley with 3 screw holes tapped into the machined face. A gasket & plate is screwed here, forming a reservoir that holds oil and the clutch gear sits in this oil. The big knob you see in the front view of the apron is the clutch engagement knob.

mcload said:

I'm hoping Chuff can get this machine back to good order and that he hasn't broken anything. From time to time we hear from an old grizzled machinist advising to just "slather an old machine with oil and start making' chips...it will be fine". With all due respect to Chuff, I'm afraid that's not the case here. His machine looks fairly clean, so whose to know.
Hindsight is always 20/20, huh?!

Click to expand...

When I was given this lathe it was rusted and seized up and I thought is was not only beyond repair but also flogged to death. Since restoring it and surfing the internet educating myself on the lathe I have seen a lot of photos & videos of similar lathes that are in far, far worse state. Compared to what I have seen, mine is in exceptional condition with very, very little wear.

Chuff

mcload said:

Glad you got it solved Chuff.
BTW, I meant no offense and used a poor choice of words.
I do not consider you nor your machine old and grizzled.
The exact opposite is true.

I'll go back into my cave now.

Click to expand...

No offense taken.

Well there's no guarantee that a South Bend clone is the same as a South Bend, but on the real South Bend, that pin DID go all the way through. I wonder if you looked with magnification, you might just find that yours did the same. That pic you posted of (what's left of your) pin makes no sense at all for retention.

The South Bend method looked like this:


That said... I didn't like the South Bend method of sharing the same pin to both retain the key and lock the collar, so I modified my worm gear and collar to separate those two functions. By doing that, I was able to adjust the collar a little tighter to take up the wear slop that had accrued on my lathe.

I put a new hole through the worm gear (in an area that does not affect operation) and key and then threaded the key to accept a small screw. That screw holds the key tight into the gear body regardless if the collar is present or not. Looks like this:



I also threaded the original hole in the collar and now use a setscrew (with a small aluminum pad underneath) that tightens against the threads on the end of the gear body:


I probably posted about this many moons ago, but I'm sure all the picture links are dead.