Sheldon 11" Lathe Issues

B

BobSchu

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Trying to get my lathe set up and I found a couple problems. When I engage the lead screw on the apron, the thread dial stops working. When the half nut isn't engaged, it works but weakly. Can't tell if it is a worn half nut or the gear on the thread dial is worn out- maybe a bit of both. The half nut engagement seems to work fine and the table moves fine and the crossfeed engages properly.

Also, the gear box won't stay engaged when set to the smallest gears on the far left. Even when holding the handle tight, it still wants to jump out of the gears. The gears seem to be in good shape, no broken teeth and engagement seems okay. May have to check the bearing to the back gear cluster? Any ideas what else I should check?
So far, everything else seems to work as it should as far as I can tell. Haven't been able to check as accurately as I'd like, but the runout at the spindle snout seems to be in the .0005 range with my crappy set up. Need to get some new indicators and magnetic mount set ups to check it better.

This is an older U drive 11" x 56" bed lathe with single handle gear box.

TIA,
Bob
 
The thread dial would stop when you engage the half nuts That means that carriage is moving with the lead screw, this is correct and working properly.

The wanting to jump out of gear is probably due to a worn bushing in the gearbox. I would take it apart and have a look.
 
JimDawson said:
The thread dial would stop when you engage the half nuts That means that carriage is moving with the lead screw, this is correct and working properly.

The wanting to jump out of gear is probably due to a worn bushing in the gearbox. I would take it apart and have a look.
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Thanks Jim, that makes perfect sense now that I think about it on the thread dial. I'm kind of a newbie to this threading stuff (and owning a real lathe)

I'll take the covers off and check the bushings tomorrow.

Bob
 
BobSchu said:
Thanks Jim, that makes perfect sense now that I think about it on the thread dial. I'm kind of a newbie to this threading stuff (and owning a real lathe)
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It's not the first time this question has come up. I can understand your concern.:)
 
Unless you're threadng I would swing the chasing dial out of engagement with the leadscrew, it saves on wear. If the gears in the quick change aren't broken, I would look for chips that may be stuck in between them.
 
Bob,

I see that same threading dial question on average 3 or 4 times a month. And that's just in the four machine specific fora that I follow here plus two on Yahoo. So the question probably gets asked 8 to 12 times a month here on H-M. So the answer isn't intuitively obvious to many folks. :)

I'm not familiar with the Sheldon 11". If it has separate drives for turning and threading, then it makes sense to keep the threading dial disengaged when you aren't threading. However, if like many older US built lathes 12" and smaller the lead screw drives the carriage for both threading and turning, disengaging the threading dial when you are not actually cutting threads increases the probability of damage to the half nuts and lead screw because you are always engaging the half nuts blind. Sorta like shifting a manual vehicular gearbox without disengaging the clutch. I have an Atlas 3996 that I bought new in 1981. The threading dial on it hasn't been disengaged more than a few times in 34 years. Everything on it is still original, including the half nuts. So whether disengaging the dial is a good idea or not depends upon the machine.
 
wa5cab said:
Bob,

I see that same threading dial question on average 3 or 4 times a month. And that's just in the four machine specific fora that I follow here plus two on Yahoo. So the question probably gets asked 8 to 12 times a month here on H-M. So the answer isn't intuitively obvious to many folks. :)

I'm not familiar with the Sheldon 11". If it has separate drives for turning and threading, then it makes sense to keep the threading dial disengaged when you aren't threading. However, if like many older US built lathes 12" and smaller the lead screw drives the carriage for both threading and turning, disengaging the threading dial when you are not actually cutting threads increases the probability of damage to the half nuts and lead screw because you are always engaging the half nuts blind. Sorta like shifting a manual vehicular gearbox without disengaging the clutch. I have an Atlas 3996 that I bought new in 1981. The threading dial on it hasn't been disengaged more than a few times in 34 years. Everything on it is still original, including the half nuts. So whether disengaging the dial is a good idea or not depends upon the machine.
Click to expand...


Thanks, I usually disengage the threading dial when I'm not threading as it is pretty worn already. Not surprising, considering this machine was probably made in 1943 or so and everything that I can see is still original to the machine. Only one leadscrew drives both the carriage and the dial, so it makes sense it doesn't need to be engaged at all times. Also, a good chance the half nuts are probably a bit worn even though they engage fine. Not sure where I'll find new ones- may have to make some.

I'm pretty sure the gear box has worn bushings so that is another area I need to address before I start threading. Also may have to make new bushings as I'm not sure there is a source for them any more for these very old machines.

Bob
 
Maybe someone knows of a source. The only ones I'm familiar with are for Atlas, Clausing and Logan.
 
If the gear box has bushings, and it may, you can get Oilite bushings from McMaster-Carr. Just be sure to measure the amount of interference and adjust the OD of the bushings to fit the housing bore with about a 1/2 to 1 thousandth interference. Any more than that, you could split your cast iron housing! After installation, if the shafts will not go, get you a hand reamer or adjustable reamer and ream out the holes so the shafts will pass through. You may also need to make new shafts, too.

Edit: You may not be able to get the exact length of bushing you need. Just get an longer one and cut it to the length needed. What's left over, may make another bushing, if ordered long enough!
 
4gsr said:
If the gear box has bushings, and it may, you can get Oilite bushings from McMaster-Carr. Just be sure to measure the amount of interference and adjust the OD of the bushings to fit the housing bore with about a 1/2 to 1 thousandth interference. Any more than that, you could split your cast iron housing! After installation, if the shafts will not go, get you a hand reamer or adjustable reamer and ream out the holes so the shafts will pass through. You may also need to make new shafts, too.

Edit: You may not be able to get the exact length of bushing you need. Just get an longer one and cut it to the length needed. What's left over, may make another bushing, if ordered long enough!
Click to expand...

Pulled the covers off and checked all of the shafts and holes they go through. Can't see any bushings, but may have to clean some grease off this old machine to determine if they are there. Regardless, there didn't seem to be much movement on the mainshaft- probably not even a thousandth or less. The heavy bracket the shift handle is attached to and holds the idler gears has a few thousandths of play on the shaft so I'm thinking this is all cumulative and I will need to determine where to start. This only happens on the very last and smallest gear on the far left of the gear box- the one I'm going to need the most to thread some rifle barrels I need to do. I'm a bit new to this type of machine, so I'm going to have to do a little more research on this before I start taking things apart.
Also, I noticed it gets worse as I engage the half nuts on the apron and even worse when I engage the cross feed table. So, the stress put on the drive by the engaged lead screw is pushing something out of line, obviously.
I've looked for a parts manual for this 11" machine, but even the ones I've been able to find don't cover the older machines with the single handle gear box and U drive. Have to keep searching. I guess I could call Bourne and Koch but I'm reluctant to pay $100 for a copy of an old manual.... ;)

Thanks for all the help guys and keep the ideas coming.

Bob
 
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