Back Gear

[Manx57]

Hello, I have just bought a 1940 South Bend lathe the first lathe I have ever owned so my knowledge is zero. The lathe catalogue number is 477 Z 9w x 3 1/2 taken from the serial number card, I have started to dismantle it for cleaning and have found the back gear? has teeth missing. My question is does the back gear from any model A, B or C fit? or do I need a specific type. Any help would be appreciated...

 

[packrat2]

You may be able to repair the teeth or have them done, I have seen lots of youtube videos showing how to do it...

 

[neanderthal mach]

Missing teeth on the back gear pops up from time to time. Packrat already gave you some ideas for where to find how to repair them.

Unless it was from actual crash damage, those missing teeth are almost always caused from ham fisted people trying to use those back gears to remove a tightly threaded on chuck. They were never designed nor meant for that so they break. For reasons I can't figure out and with the amount of lathes still in use with threaded spindle noses, few seem to even know about a very old machinst technique of preventing those hard to remove chucks in the first place. Those tight chucks are really caused by the threads being very slightly stretched as in any threaded connection, but also by the chuck back plate recess creating a high amount of friction between it and the face of the spindle due to the metal to metal contact. Get the chuck to rotate even by a degree or two and its then easy to remove because that friction is gone. And for any who don't yet understand how it works, those threads only attach the chuck to the spindle, the actual chuck location for both radial and axial alignment are done with the spindles plain register butting up against the chucks internal face recess and locating on that non threaded portion of the spindle. Those are what set those axial and radial alignments so the chuck goes back on in a repeatable and low run out position each time its mounted.

For any lathes that do have threaded spindles, make yourself some thin cardboard washers for each chuck and face plate. Cereal box thin or maybe a bit lighter. Because of the way cardboard is manufactured, compressed and rolled out, its remarkably consistent for its density and gauge thickness. So it won't give you any extra axial face run out on the chuck. Or if you've got any handy, I guess you could use actual thin cardboard gasket material. Whatever you use, cut it in the shape of a washer, just barely under size to the chucks recess and the hole just oversize to the spindles thread and register diameter. If its not obvious yet, that under and over size is real important, you do not want the cardboard to try and fold over on itself at any point or your alignment will be worthless. To prevent that cardboard from picking up air borne humidity and possibly causing any rusting, I'd add a few drops of oil to each of the cardboard faces. What that cardboard will do is act somewhat like a cushion and prevent that metal to metal contact that increases the friction and makes getting those chucks or face plates so tough to get off. Fix the actual cause of the problem and you then won't have the much harder and expensive to fix end result of that problem in the first place.

 

[Manx57]

You may be able to repair the teeth or have them done, I have seen lots of youtube videos showing how to do it...

I was just being a bit lazy not wanting to fix it as I had seen a model C back great for sale, thanks for the advice though

 

[Manx57]

Missing teeth on the back gear pops up from time to time. Packrat already gave you some ideas for where to find how to repair them.

Unless it was from actual crash damage, those missing teeth are almost always caused from ham fisted people trying to use those back gears to remove a tightly threaded on chuck. They were never designed nor meant for that so they break. For reasons I can't figure out and with the amount of lathes still in use with threaded spindle noses, few seem to even know about a very old machinst technique of preventing those hard to remove chucks in the first place. Those tight chucks are really caused by the threads being very slightly stretched as in any threaded connection, but also by the chuck back plate recess creating a high amount of friction between it and the face of the spindle due to the metal to metal contact. Get the chuck to rotate even by a degree or two and its then easy to remove because that friction is gone. And for any who don't yet understand how it works, those threads only attach the chuck to the spindle, the actual chuck location for both radial and axial alignment are done with the spindles plain register butting up against the chucks internal face recess and locating on that non threaded portion of the spindle. Those are what set those axial and radial alignments so the chuck goes back on in a repeatable and low run out position each time its mounted.

For any lathes that do have threaded spindles, make yourself some thin cardboard washers for each chuck and face plate. Cereal box thin or maybe a bit lighter. Because of the way cardboard is manufactured, compressed and rolled out, its remarkably consistent for its density and gauge thickness. So it won't give you any extra axial face run out on the chuck. Or if you've got any handy, I guess you could use actual thin cardboard gasket material. Whatever you use, cut it in the shape of a washer, just barely under size to the chucks recess and the hole just oversize to the spindles thread and register diameter. If its not obvious yet, that under and over size is real important, you do not want the cardboard to try and fold over on itself at any point or your alignment will be worthless. To prevent that cardboard from picking up air borne humidity and possibly causing any rusting, I'd add a few drops of oil to each of the cardboard faces. What that cardboard will do is act somewhat like a cushion and prevent that metal to metal contact that increases the friction and makes getting those chucks or face plates so tough to get off. Fix the actual cause of the problem and you then won't have the much harder and expensive to fix end result of that problem in the first place.

Thanks for the advice I will remember this when I get it going

 

[johnoder]

477 Z is a Model B, so you do have the geared apron with power cross feed.

 

[stephen thomas]

the actual chuck location for both radial and axial alignment are done with the spindles plain register butting up against the chucks internal face recess and locating on that non threaded portion of the spindle

This has been argued off and on, here, in real life, and on other forums.
People who i have faith in with better credentials than mine don't think it is true.
I don't either.

But then again, i set the back gears when taking a chuck off and have never had a moments problem.
Just don't ever hammer. Twist loose with whatever spanner, bar, or extension is appropriate to the tooling being removed, but don't hammer. I do not leave it in back gear when putting on chucks, Jacobs rubberflex, or faceplates. I leave the belt engaged and just spin on spindle tooling to a nice, slight, "tap" against the register face.



smt

 

[Manx57]

You guys are very knowledgeable but have gone off topic from my original post question: does the back gear from any model A, B or C fit? or do I need a specific type

 

[jim rozen]

"But then again, i set the back gears when taking a chuck off and have never had a moments problem."

My personal opinion is that most gear tooth damage is caused by folks engaging back gears, tumbler reverse gears, and QC gearbox gears, while under power. The forces involved in removing a chuck are modest compared with actual cutting forces.

My other opinion is the difference between A, B, and C model 9" lathes do not involve the headstock gears.

 

[johnoder]

"But then again, i set the back gears when taking a chuck off and have never had a moments problem."

My personal opinion is that most gear tooth damage is caused by folks engaging back gears, tumbler reverse gears, and QC gearbox gears, while under power. The forces involved in removing a chuck are modest compared with actual cutting forces.

My other opinion is the difference between A, B, and C model 9" lathes do not involve the headstock gears.

May even be Mr. Rozen that has the nice photos of pins inserted to be worked into usable teeth?

 

[jim rozen]

That would be the Seneca Falls lathe that came with a previous owner's fixes on multiple gears. It was so nicely done I had to document it, and keep the old gears after I replaced them. First three show the pickoff gear for the reverse tumbers (obviously NOT damaged because of chuck removal) and the last shows - barely - the repair to the smaller back gear on the cone pulley.

 

[swells]

I have uploaded three back gears files at the bottom of the page for you here:

Facts From The Experts

9-10K Headstock-Tailstock Units with Sub-Units

www.wswells.com

The files are:
1 - http://www.wswells.com/fte/HS-TS/NK-HS-TS/NK-back-gears/9N-10K-back-gears-interchange.pdf

2 - http://www.wswells.com/fte/HS-TS/NK-HS-TS/NK-back-gears/9N-10K-back-gears-removal.pdf

3 - http://www.wswells.com/fte/HS-TS/NK-HS-TS/NK-back-gears/9N-10K-back-gears-adjustment.pdf

After reading these, I believe you will realize there are at least 3 different back gear shafts, but you should be able to adjust the length with shims or remaking a bushing length to compensate. A Workshop 9C would have a shorter gear assembly that a side oiling Workshop 15, and a newer 10K is shorter than the Workshop 9C. South Bend shipped the spacers I believe, with the later model back gear part to intechange if required, or they offered the spacers separately, I can't recall right now.
Hope that's helpful.

 

[Manx57]

I have uploaded three back gears files at the bottom of the page for you here:

Facts From The Experts

9-10K Headstock-Tailstock Units with Sub-Units

www.wswells.com

The files are:
1 - http://www.wswells.com/fte/HS-TS/NK-HS-TS/NK-back-gears/9N-10K-back-gears-interchange.pdf

2 - http://www.wswells.com/fte/HS-TS/NK-HS-TS/NK-back-gears/9N-10K-back-gears-removal.pdf

3 - http://www.wswells.com/fte/HS-TS/NK-HS-TS/NK-back-gears/9N-10K-back-gears-adjustment.pdf

After reading these, I believe you will realize there are at least 3 different back gear shafts, but you should be able to adjust the length with shims or remaking a bushing length to compensate. A Workshop 9C would have a shorter gear assembly that a side oiling Workshop 15, and a newer 10K is shorter than the Workshop 9C. South Bend shipped the spacers I believe, with the later model back gear part to intechange if required, or they offered the spacers separately, I can't recall right now.
Hope that's helpful.

Thank you very much

 

[chipss]

I'm late to the game but here's your answer if the small gear is the damaged one.

South Bend Lathe 9" Back gear repair kit | eBay

9" South Bend Lathe Backgear repair kit. Here we have an inexpensive way to repair the small gear on a SB 9" lathe. Just read the instructions with the pictures shown. The gear is made of 4140 alloy. It comes with the Loctite needed for installation.

www.ebay.com

 

[HairFree]

Missing teeth on the back gear pops up from time to time. Packrat already gave you some ideas for where to find how to repair them.

Unless it was from actual crash damage, those missing teeth are almost always caused from ham fisted people trying to use those back gears to remove a tightly threaded on chuck. They were never designed nor meant for that so they break. For reasons I can't figure out and with the amount of lathes still in use with threaded spindle noses, few seem to even know about a very old machinst technique of preventing those hard to remove chucks in the first place. Those tight chucks are really caused by the threads being very slightly stretched as in any threaded connection, but also by the chuck back plate recess creating a high amount of friction between it and the face of the spindle due to the metal to metal contact. Get the chuck to rotate even by a degree or two and its then easy to remove because that friction is gone. And for any who don't yet understand how it works, those threads only attach the chuck to the spindle, the actual chuck location for both radial and axial alignment are done with the spindles plain register butting up against the chucks internal face recess and locating on that non threaded portion of the spindle. Those are what set those axial and radial alignments so the chuck goes back on in a repeatable and low run out position each time its mounted.

For any lathes that do have threaded spindles, make yourself some thin cardboard washers for each chuck and face plate. Cereal box thin or maybe a bit lighter. Because of the way cardboard is manufactured, compressed and rolled out, its remarkably consistent for its density and gauge thickness. So it won't give you any extra axial face run out on the chuck. Or if you've got any handy, I guess you could use actual thin cardboard gasket material. Whatever you use, cut it in the shape of a washer, just barely under size to the chucks recess and the hole just oversize to the spindles thread and register diameter. If its not obvious yet, that under and over size is real important, you do not want the cardboard to try and fold over on itself at any point or your alignment will be worthless. To prevent that cardboard from picking up air borne humidity and possibly causing any rusting, I'd add a few drops of oil to each of the cardboard faces. What that cardboard will do is act somewhat like a cushion and prevent that metal to metal contact that increases the friction and makes getting those chucks or face plates so tough to get off. Fix the actual cause of the problem and you then won't have the much harder and expensive to fix end result of that problem in the first place.

Agree except for one thing. Axial alignment is achieved by the thread flanks on spindle nose and accessories. Lathes out of the factory had clearance between the non threaded collar on the spindle nose and chucks, faceplates etc. That is a common misconception.

 

[animal12]

Wasn't there a guy pedaling a kit here for fixing these gears ?
animal

 

[john.k]

I used to buy ex school lathes ...and many and varied were the broken gears ......most common fix was to braze the tooth gap ,and recut the teeth ........common phosphor bronze filler is equal in every way to cast iron.

 

[4GSR]

I've been running my 9" SBL for years with missing teeth in the back gears. Never miss a beat. Someday, I'll get around to fixing it.

 

[Peter.]

If it's the bull gear that's missing teeth I have a new in the box one for a 9" South Bend.