Thread: Worn Drive Siezed

Hi All,

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.

IMG_20211104_140719.jpgIMG_20211104_140750.jpgIMG_20211104_140800.jpgIMG_20211104_141008.jpgIMG_20211104_141015.jpgIMG_20211104_140818.jpgIMG_20211104_141023.jpg

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 siezed. 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.

IMG_20211107_160316.jpgIMG_20211107_160350.jpg

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.

Originally Posted by chuff

IMG_20211107_160350.jpg

Bit of precision angle grinder work? Slice the collar off where the pin goes through (both sides) and replace?

Michael

Why is the worm drive seized? Is there an interlock with the half nuts that is not in the correct place?

Originally Posted by Michael G

Bit of precision angle grinder work? Slice the collar off where the pin goes through (both sides) and replace?

Michael

I'm not sure what you mean. Cut it how?

Originally Posted by lamestllama

Why is the worm drive seized? Is there an interlock with the half nuts that is not in the correct place?

I have no idea, but prior to repairing the clutch engagement it was working fine as I could engage the gearbox, the threaded lead screw would rotate and I could engage the half nuts and the apron would move along the bed of the lathe as expected. After repairing the clutch engagement I was able to test that it was all working well, both longitudaly and cross-feed, which they were for a few minutes, and then it just seized up. I've dismantled the apron and can confirm that all parts within have free movement, as can be seen in the video I provided a link to, with the exception of the worm drive.

This is the apron stripped down as it is now. As you can see there are no interlocks or half nuts to foul anything.

IMG_20211107_231601.jpg

I also removed the gearbox and the lead screw as a single unit and while holding the non-threaded end of the lead screw where it exits the gearbox in a vice I slid the apron onto the lead screw in this stripped down state and can confirm that the worm drive does not want to budge. The remaining gear behind the worm drive as well as the clutch gear riding the worm drive are both free to move apart from the fact that the clutch housing can't rotate as the worm drive it's meshed with cannot rotate.

That's as best as I can explain it. If you have any specific questions you'd like answered, please ask.

Thanks to both of you for your replies.

Chuff

Originally Posted by chuff

This is the apron stripped down as it is now. As you can see there are no interlocks or half nuts to foul anything.

IMG_20211107_231601.jpg

That's as best as I can explain it. If you have any specific questions you'd like answered, please ask.
Chuff

So what is that rod that i can see from just right of the worm wheel heading of in to the casting in the direction of the half nut closing mechanism?

What happens if you change the position of the half nut lever?

Originally Posted by lamestllama

So what is that rod that i can see from just right of the worm wheel heading of in to the casting in the direction of the half nut closing mechanism?

What happens if you change the position of the half nut lever?

Hi lamestllama,

That rod is the lock out rod that locks out the half nut engaging lever if the feed engaging lever is set to the upper or lower position to provide drive to the longitudinal or cross-feed mechanisms. It only allows the half nut engaging lever to be engaged when the feed engaging lever is set to the middle position. It's operating as expected.

Nothing that I can see is fouling or jamming the worm drive gear. It seems to be seized within its bore.

The worm drive gear has been rotating fine since I first restored the lathe as I've been able to engage the half nuts on many occasions. It only failed after I repaired the lathe's ability to provide longitudinal and cross-feed drive so I'm wondering if & how this may have caused the worm drive gear to seize as nothing else was changed apart from the clutch finally being able to engage.

If the worm seized whilst in testing did it cause any other damage to the gear train or associated parts of the lathe or did the drive belts just slip?
Have you tried holding the keeper ring and turning it with vice grips or Multies or similar?

Originally Posted by pipeclay

If the worm seized whilst in testing did it cause any other damage to the gear train or associated parts of the lathe or did the drive belts just slip?
Have you tried holding the keeper ring and turning it with vice grips or Multics or similar?

Hi pipeclay,

Thanks for your post.

As far as I can tell every other part of the lathe/gear train is working fine, and yes, when it seized up the drive belt just slipped & I turned it off immediately.

I have tried to rotate the worm drive by gripping the keeper ring/collar that holds it in place with multi grips and then vice grips but it would not budge. In addition, as stated previously:

I also removed the gearbox and the lead screw as a single unit and while holding the non-threaded end of the lead screw where it exits the gearbox in a vice I slid the apron onto the lead screw in this stripped down state and can confirm that the worm drive does not want to budge.

I'm far from an expert but to me it very much seems to be seized within the bore and not fouled or jammed in any way.

I'm wondering if I apply heat to the bore in the apron that holds the worm drive in place with a MAP gas torch if that may expand the casting and release its grip on the worm drive but I'm unsure if this will help or make things worse.

Michael G suggested:

Bit of precision angle grinder work? Slice the collar off where the pin goes through (both sides) and replace?

If I understand his suggestion correctly, and I may be wrong, but if he's suggesting that I cut the pin that's holding the collar on the worm drive off by using a Dremel or similar, by cutting a "V" around the pin as well as the worm drive and collar, then that should allow me to remove the collar but if the worm drive is seized within its bore then the removal of the collar won't necessarily allow the worm drive to be removed. If Michael G's suggestion means something different, then I would need more clarification from his post as to what it is he is suggesting I do. If, however, this method was to work I'm not sure I'd be able to find replacement worm drive, collar & parts. Are such parts still available, either new or used?

Hi Guys,

From the pictures it looks to be full of crud ! Something could have got forced between the worm and support housing.

A piece of bent rod might get into the pin hole to enable it to be turned.

Originally Posted by BaronJ

Hi Guys,

From the pictures it looks to be full of crud ! Something could have got forced between the worm and support housing.

A piece of bent rod might get into the pin hole to enable it to be turned.

Hi BaronJ,

Thanks for your reply.

I'm not sure exactly which picture you're referring to but I can assure you there is absolutely no crud anywhere within the apron. I'm not sure if you viewed the video I linked to in my first post, which was taken before I disassembled the apron as far as I could, but the video clearly show the apron and all gears within are in pristine, clean condition. just in case you haven't, here's the link: https://www.youtube.com/watch?v=lTTUGVvQdKE

If you're referring to the casting that holds the worm drive, it has discoloration and is a rough casting but it is perfectly clean.

As for something jammed between the worm drive and support housing, I have checked it and I can't see any issues, however, I will have a much closer look just to be certain.

Thanks.

Chuff

Keen to find a solution I also posted this problem on another forum and the problem was resolved.

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.

IMG_20211110_110957.jpg

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.

IMG_20211110_115940.jpg

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 to everyone for their replies and considerations. Problem solved.

Chuff