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Pools Special Back Gear

Advice sought

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The Mad Professor05/03/2021 15:32:01
9 forum posts

I have a 4" Pools Special lathe, 1934 vintage, so no manuals available at all. Has anyone "out there" ever dismantled the back-gear mechanism so that the back-gear countershaft can be removed from the lathe? I want to fit a decent lubrication point and need to get the shaft out to end drill it for an oil nipple. I am reluctant to just go at it without any prior knowledge as it seems that an impossible situation is present, in that the spindle on which the back-gear cluster rotates appears larger in diameter that the holes in the headstock casting supporting it and there does not seem any way that I can withdraw the spindle.

You either know what to do or you don't...

Thanks

Howard Lewis05/03/2021 17:53:27
4662 forum posts
10 photos

Making provision for oil lubrication, (rather than grease ) sounds to be an excellent idea.

Don't know the lathe, (Lathes UK illustrations seem to show a pin in the casting at the "chuck" end of the casting, and an oil cup at the rear end of the casting..The smaller gear also appears to be pinned to the shaft.) Longer study may provide some clues. Back Gear looks to be engaged by rotating the lever at the back end of the shaft, which suggests that there is an eccentric involved somewhere.

Wild guessing; but it could be that the shaft is located endwise by the pin at the chuck end, engaging in a groove, whilst the gears are run on a journal which is eccentric to the shaft. In this way, rotating the shaft with the small lever, will throw the Back Gear cluster in and out of mesh. But there must also be some means of clamping the drive pulleys to the mandrel, which will need to be disengaged when back Gear is being used., to prevent everything locking solid.

Once the end locating pin has been removed, and the pin from the small gear, it ought to be possible to remove the shaft (Might need to be gently driven out )

The lathe can then be used to drill and tap the chuck end of the shaft for the oil nipple and oilway, before being cross drilled;

(IF the oil cup at the lever end does not provide this function. Possibly by a groove under the oil cup leading to a cross drilling, a longitudinal drilling, and cross drillings into the journal(s )

Once clean, it can be reinstalled and you are away!

HTH

Howard

not done it yet05/03/2021 18:33:26
5776 forum posts
20 photos

I am wondering why you are lubing via the shaft. Is there no way to lubricate (through) the bearing? Thinking here an oilite bearing might be appropriate.

Clive Foster05/03/2021 18:50:14
2625 forum posts
91 photos

I had a Pools special about 45 years ago and recall pulling the back gear shaft out with no significant issues.

As I recall things Howard is correct in stating that the vertical (taper?) pin at the headstock end retains the assembly so once that and the clamp screw are removed the pin ought to just pull out. I'm fairly sure I twisted mine during removal. Whether this was to release the usual old lathe crud build up or find the right alignment so things would pull out I now know not.

I want to say the the eccentricity is got by having larger bobbins keyed to the small through shaft but I may be mixing it up with another machine. If so the small shaft will need rotation to find the gap in the casting through which the key(s) must pass. Another bobbin retention possibility is a grub screw aligned with an oil hole so a screwdriver can be inserted to release things. However if it was the grub screw option I suspect I'd have had problems and remembered it being hard, if not exactly why.

Clive

Robert B05/03/2021 20:00:30
15 forum posts
6 photos

My Pools is still buried under my son's tools, debris and junk. It's waiting for is garage and workshop to be built and until then it is inaccesable. His roof shoud arrive next week and I hope to be able to shift the stuff in a couple of weeks. I still have a gear to investigate and can have a look then. But until then...

Robert

Windy05/03/2021 20:02:36
avatar
839 forum posts
166 photos

I had a Pool Special in 1970 the previous owner had machined the headstock and made spindle bearing detachable top clamps so spindle could be lifted out.

The Mad Professor06/03/2021 09:14:50
9 forum posts

Hi Clive,

Thanks for the advice. Clearly I need to have a little poke about and look at it carefully, but it would seem that your advice is spot on. When I've finished machining the job I'm on, I'll have an investigation. The back-gear bobbin is definitely on an eccentric, which is probably located on to the shaft with a grub screw accessible through one of the spacers which also have grub screws. It will need a good look to find the pin or screw.

Mark H06/03/2021 20:22:58
16 forum posts
3 photos

Just picked up a pools 4" special that I started to strip down today, total newb regarding lathes

Regarding back gears, loosen the grub screws on the spacers, then the shaft knocks out from the right, my back gears don't engage properly, the shaft in mine is bent which would explain it, dunno what I'm going to do about it yet.....

The Mad Professor14/03/2021 09:13:24
9 forum posts

Howard is correct - I removed the taper pin which allows the back-gear selector lever to be pulled off. There is a bush axially pinned to the shaft which needs to be removed first - not easy with 90 years of congealed oily muck holding it in, but once this is removed, the spacer grub screws can be slackened off and the shaft then slides out to the left.

The back-gear bobbin is on a steel tubular shaft which runs on the eccentric steel shaft. Not a good idea running steel on steel - hence the desire to put in a decent method of lubrication. The eccentric shaft is located in the lathe bracket by the bush, which isn't obvious under the muck, but once cleaned it can be pulled out to the left.

Many thanks to all contributors.

Brian Wood14/03/2021 12:29:49
2380 forum posts
37 photos

If the Professor will forgive me for the intrusion,

Mark

You can recover a bent shaft readily enough, even a short one like a back gear shaft. It is hard work mind but perseverse.

Support the two ends in wooden Vee blocks, sitting on a concrete floor, rotate the shaft so that the high point is uppermost and belt the hell out of it with a lump hammer down a length of 3 X 2 timber. Check it from time to time by gripping one end in your 3 jaw chuck and rotate it to see how you are doing.

Realign as necessary on your 'Vee' blocks and chase the high spot out until you can get the shaft to run true within a few thou over it's length

I have recovered a 3/4 inch diameter gear box shaft by this method.

If you have access to a press, it will save you some effort but check very frequently if using that approach since you have no 'feel' about how the metal is yielding and it would be all too easy to overshoot the sweet spot.

Regards Brian

Howard Lewis14/03/2021 16:10:52
4662 forum posts
10 photos

+1 for Brian's advice.

It is not unusual for a crankshaft that has distorted during heat treatment to be straightened.

Then shaft is set on Vee blocks under a press and rotated so that the run out can be measured with a DTI. It is then set "hogging" (Bend uppermost ). The press is then brought to bear on it to depress it by just less than half the run out. It is then unloaded and rotated, to recheck run out. The press / measure sequence is repeated until the run out comes withing the tolerance..

If your shaft or tube is bent, give it the same treatment.

Howard

Brian Wood14/03/2021 17:50:30
2380 forum posts
37 photos

Hello Howard,

I beg to differ, surely the press should go just over the indicated mid point to allow for spring in the material.

Regards as always

Brian

Howard Lewis14/03/2021 18:01:22
4662 forum posts
10 photos

Agreed Brian, but I advocate making haste slowly, rather than risk overdoing things.

Slowly slowly catchee and all that (Possibly over cautious, but rather tortoise than hare )

As always, we tread the same path.

Regards

Howard

Mark H20/03/2021 13:40:45
16 forum posts
3 photos
Posted by Brian Wood on 14/03/2021 12:29:49:

If the Professor will forgive me for the intrusion,

Mark

You can recover a bent shaft readily enough, even a short one like a back gear shaft. It is hard work mind but perseverse.

Support the two ends in wooden Vee blocks, sitting on a concrete floor, rotate the shaft so that the high point is uppermost and belt the hell out of it with a lump hammer down a length of 3 X 2 timber. Check it from time to time by gripping one end in your 3 jaw chuck and rotate it to see how you are doing.

Realign as necessary on your 'Vee' blocks and chase the high spot out until you can get the shaft to run true within a few thou over it's length

I have recovered a 3/4 inch diameter gear box shaft by this method.

If you have access to a press, it will save you some effort but check very frequently if using that approach since you have no 'feel' about how the metal is yielding and it would be all too easy to overshoot the sweet spot.

Regards Brian

Thanks Brian, I'll give it a go, might just have a go at making a new shaft as the first project, once mine is back together again....

Howard Lewis20/03/2021 17:02:47
4662 forum posts
10 photos

Hopefully, if you do make a new shaft for the Back Gear, you won't need the Back Gear.

Otherwise you are in the "There's a hole in my bucket, Dear Liza" territory!

The cente lathe is the one machine tool capable of reproducing itself, so Go Ahead!

Howard

Mark H21/03/2021 08:17:59
16 forum posts
3 photos

I've also got a mini lathe so might be able to use that, see how it pans out....

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