9" Toolroom lathe carriage stuck

[animal12]

A bud asked me to come over & look at his lathe a South Bend 9A . It's one of the fancy
ones large dials , spindle cover on the headstock & came with a taper attachment . The
Numbers on the change gear plate xx8344ZD I cant read the first two digits . Ok so now the the problem , the carriage
will only move @ 3/4"- 1" . The hand wheel for moving the apron will turn from @
one o-clock to 12 o-clock on , so not even a full revolution .We removed the saddle & the
lead screw support thinking we would be able to slide the apron off the lead screw but
no go , it will still only move the same 3/4-1" & stop & its a hard stop . So next we removed the taper pin holding the hand wheel on & pushed the pinion shaft into the apron so
the pinion gear had no contact with the gear that contacts the rack & still no
movement only the 3/4" - 1" . When it stops it's like it just hit a brick wall , it's a hard stop We tried spinning the input gear for the gearbox to try
to drive the apron off the leadscrew but the bolt the holds the gears on loosened so
that was a dead end . I marked the gear that runs in the rack & in the almost full
revolution the handwheel makes the rack gear only moves @ 1/3 of a revolution .
Unfortunately the unit is stuck maybe a quarter down the leadscrew from the gearbox.
We were hoping we might be able gently push the right side of the leadscrew down
enough to disengage the rack gear from the rack to slide the assembly off , but it's just to close to the gear box & don't want to bend the leadscrew . I've had one of these lathes into
as many pieces you can get with out removing the feet & I'm at a loss as to what the problem just might be . We left the required parts reinstalled for the weekend so we could think
about this some more . I'm going to borrow a bore scope & see if I can see any more but
I'm at a loss on this .
Any of you folks have any ideas ?
sorry for the paragraph spacing , I copied & pasted the whole text & something got lost in the translation
thanks
animal

 

[animal12]

Want to add a few things I forgot in my lengthy post above.
I do have the saddle & apron separated . Unless I can see something fishy when I go back next monday with a bore scope I will pull the headstock & then pull the geabox-leadscrew & apron as a assembly . The guy that owns the lathe is a machinist & out of his 7 lathes he still uses this SB lathe just about every chance he gets he likes it so much . He called ma cause he knows that I have stripped one of these puppies down before . I just wish you could get to the gearbox mounting screws without pulling the headstock . He has owned several SB lathes in the past & he has been kind enough to send unused parts my way . A few years back he sentme home with a brand new maybe used once telescopic steady & follow rest for a 10 K he used to own . I was able to trade them here for a follower & steady for my 9A within a few months & last week he sent me home with a brand new set of the metric transposing gears for my 9A lathe . I try to help him any way I can .

Will report back hopefully on monday what we discover
thanks
animal

 

[jim rozen]

Check to verify the clamp that holds the rear of the carriage from lifting off the bed is slacked. Another worry is the lead screw goes through a bronze worm gear inside the carriage, and there is a steel key which allows the keyway in the leadscrew to drive that gear. The key has two ears that keep it retained in the assembly. If one of those ears is worn it might allow that key to jam in place and lock up the carriage.

Any chance the half nuts are stuck engaged, even though the handle says they're not?

 

[Illinoyance]

Unclamp the TA anchor from the bed and see if that helps.

 

[chipss]

You've eliminated the handwheel gear. Carriage lock hitting something? So unless something is hitting and stopping the ways (illogical) the only thing that could be holding it up is the drive from the lead screw. It's been years since I had my 9 apart but is there enough room that you can take the worm gear apart without already having the carriage off? IIRC there's a pin that holds it together. Perhaps the key is hitting a burr on the lead screw. Purely a guess but.....
**Pic is from a buddy's heavy 10.

 

[animal12]

I have everything removed that can be removed from the apron with it still having the lead-screw in the worm gear .. Saddle has been removed , hand-wheel off & pinion gear pushed in so the teeth aren't in contact with the larger gear of the rack gear stack . I'm still thinking that it's something under the rack gear just cause of the way it makes such a hard stop . We've been trying to avoid pulling the head-stock , but it's in the on top of the furthest left rack screw & also covering the the gear box mounting screws . I need to go pickup the bore-scope this weekend & will use that before we go any further . If I don't find anything I guess we'll pop the head-stock & then get the apron with leadscrew on the bench for a autopsy . Wil report our post-mortem findings .
thanks
animal

 

[michiganbuck]

I have seen machines with a totally worn-out lead screw nut slip a thread and then move one turn or so and then lock up with a hard stop on one direction and on the other direction

 

[animal12]

This machine is pretty tight . But we'll find-out what the story is on monday hopefully
animal

 

[Gard]

Is it possible that the rack has a damaged tooth or something stuck between the teeth? I think you can remove the screws that hold the rack on, perhaps that will free up something.

 

[animal12]

There is one rack screw, the furthest left one that is partially covered by the headstock . I'm loading up tools & other things that may or may not help us get to the bottom of this . Picked
up the bore-scope yesterday .
Will report findings after autopsy
thanks
animal

 

[jim rozen]

How's the jam-up going? Unjammed yet?

 

[animal12]

No , sorry I haven't gotten back , one of my sons got married this weekend & I have been buried with honey do's & relatives . I'll be back over there in a few days .
animal

 

[jim rozen]

congratulations!

 

[animal12]

thanks , defiantly a night to remember !!!
animal

 

[animal12]

Ok unit has been dissembled . The headstock was much tougher to remove that my 9A . The bolt for the headstock on the right side is a real bugger to get to . I think it will be replaced with a stud when we reassemble the lathe . With the apron sitting on the bench there is still resistance while turning the hand wheel , I left him with orders to dissemble along with directions on how to do it & I left him with my rebuild book . Looking at the serial # data I could find , it looks to be a 1959 model , waiting to hear from Steve to confirm . Also have the gearbox upside down for cleaning with instructions on how to get at it . The worm in the apron was fine rotated freely . From what I could see this machine is a victim of a air gun for too many years . I removed the air hose from it's location behind the lathe & the owner agreed . I think he'll be fine after a good cleaning . I wrote a brief history of this lathe in post # 2646 on the " lathe serial numbers wanted " post . Once we got it apart into these smaller assembly's he finally agreed with me that these lathes aren't rocket science , but I will be back at his shop for a once over before reassembly . Thanks for all the input folks .
thanks again
animal

 

[jmm03]

broken gear tooth or something jammed up in a tooth? Pin backed out of the worm drive? Jim

 

[animal12]

I couldn't see anything , He's going to give me a buzz when he's cleaned things up . I told him to save anything that came out during cleaning . Worm pin was still in place & worm spun freely . For the age & use the machine get's I was really surprised just how little crap was caked in all the dark corners . Maybe the air does some good ? He told me that he had been reading the manual & my rebuild book & was thinking the worst since the manual says that your supposed to take the lathe apart & clean it every so many years . I'm betting that he's not the only guy to not stop & clean his lathe every so many years .
thanks
animal

 

[chipss]

I am amazed at how much small chips and crud the saddle will accumulate on my 9 inch. I don't use air to blow things off on mine and draining what little oil the saddle holds perhaps yearly shows a lot of crud. And this machine is an occasional use hobby machine. If I were to guess, perhaps an hour per month average.

 

[neanderthal mach]

The more you understand about the internal workings of any machine tool the easier it is to "judiciously" apply compressed air directed to where it's ok and understand where it isn't. Most times I'll use a 2" paint brush for sweeping chips off the lathe ways and flat surfaces, but will use either air or vacuum on my mill a lot more just to prevent chip re-cutting. Compressed air on a lathe helps when boring or internal thread cutting, but that can also drive even more chips inside the chuck with shorter length through holes. I'll use it then, but always feel a bit guilty. :-)

And I'd very much agree, little to no information is given in most user manuals about the requirement of semi regular preventative maintenance like that disassembly & cleaning. I pull the slides, carriage & tail stock on my lathe and X,Y assembly on my mill every year or two depending on the amount of use. And with lathe chucks, the first time they show any binding at all. Discolored or even black lube oil is caused from not enough lube, wear & contamination and that increases even more wear on what are supposed to be precision surfaces. A further tip I learned the hard way, any threaded item used a lot such as carriage and tail stock locks needs thread lubrication and that cleaning as well. And they last at least 10 X longer with lube than without. Oil properly used and often enough helps to flush out those wear particles and contamination, grease used in the wrong areas does the opposite.

 

[animal12]

Well lathe is reassembled & back in action . All it was , was a bunch of crap on top of a bunch more crap in the right place to hold things up . Kinda like I used to tell my kids , you ever wonder what that white crap is on top of a pile of chicken s..t ? It's just more chicken s..t . He's extremely happy I talked him into taking it apart & cleaning it . I told him it wasn't rocket science ( he started out as a machinist at JPL )
and after this exercise he fully agrees & now he understands a lot more about how what does what . Thanks again for all the input & suggestions folks . We ended up with a happy camper here.
Thanks again
animal