South bend 9 cross slide

[finsruskw]

I bought that manual (copy) from Grizzly and found it to be somewhat vague in some aspects.

The nut that was on my 9A was not drilled and there was nothing in the threaded hole, except petrified swarf
The replacement nut was not drilled either.

I installed the replacement and it did lessen the backlash somewhat but not as much as I was hoping for.

 

[mcload]

Thank you for the info about the lack of hole.

By the way, I may have found a suitable replacement for the slotted screw on this nut.
It is at McMaster Carr; 10 bucks for a pack of ten. It is item number 92785A554.
These are ½" long; have a conical end; hex head; and stainless steel. (3/8" length is
available if you prefer). The conical end should do the trick, tho I have not yet tried.

 

[finsruskw]

Thank you for the info about the lack of hole.

By the way, I may have found a suitable replacement for the slotted screw on this nut.
It is at McMaster Carr; 10 bucks for a pack of ten. It is item number 92785A554.
These are ½" long; have a conical end; hex head; and stainless steel. (3/8" length is
available if you prefer). The conical end should do the trick, tho I have not yet tried.

Is the part number for the pin PT358NK1??

I am familiar with the conical end set screws as they are also used as bearing retainers on Cub Cadet mechanical PTO's
And, since my last post, I have finally figured out just what the deal is with the pin.

Correct me If I am wrong, but does it not insert into a hole that is supposed to be in the SIDE of the post of the nut and forced into the CS body by downward pressure applied by the slotted screw, thereby forcing it up against the CS body and stabilizing the CS screw in the body?

Seems like a good project for someone with a small lathe to make some of these.

 

[mcload]

Is the part number for the pin PT358NK1??

I am familiar with the conical end set screws as they are also used as bearing retainers on Cub Cadet mechanical PTO's
And, since my last post, I have finally figured out just what the deal is with the pin.

Correct me If I am wrong, but does it not insert into a hole that is supposed to be in the SIDE of the post of the nut and forced into the CS body by downward pressure applied by the slotted screw, thereby forcing it up against the CS body and stabilizing the CS screw in the body?

Seems like a good project for someone with a small lathe to make some of these.

Yes, that is exactly correct. Sorry, I don't have the part number offhand.
If using a new repro nut, there is a tiny bit of sharp burr where the pin exits the
nut. This has to be filed smooth or else the pin can hang up on it.

I can't imagine how difficult it would be to recreate that part; it is so very small!
Not only does it require a conical end and a straight slot, but the part that pushes
against the body has to have a convex end to match the curvature of the mounting hole!

 

[mcload]

I bought that manual (copy) from Grizzly and found it to be somewhat vague in some aspects.

The nut that was on my 9A was not drilled and there was nothing in the threaded hole, except petrified swarf
The replacement nut was not drilled either.

I installed the replacement and it did lessen the backlash somewhat but not as much as I was hoping for.

Yeah I hear ya'. To total minimize that backlash, you have to replace the ACME thread too, which by the way, is kind of
hard to come by these days. It is an ACME 7/16-10 Left Hand Thread. McMaster Carr doesn't carry it. You can usually buy a
foot off the auction site, and I assume its made correctly.
You basically have to cut the old thread off the shaft; drill and ream about an inch into that larger shaft; turn down
the new threaded rod to a slip fit; drill a small air-escape hole; saturate with a thread lock solution; push it in; allow to dry,
then drill and pin the tang into the body. The guys that sell the repro CS nuts say they can do that for you, but
I don't know the cost....prob not cheap.
That's why it so very important to keep those threads lubricated to minimize wear.

 

[finsruskw]

I currently, with the new replacement nut, have about .012 backlash including about .003in the dial end that I can shim out (I hope)

So, maybe I should consider well enough??
Thank you very much for your input.
Very much appreciated.

Dave S.

 

[SLK001]

Curious as to where you found that parts page?

There is a US Army Technical Manual for the 9" SB lathe, #TM 9-3416-235-14&P. The manual is public domain material. The copy I have is: ARMY_CL670Z.PDF. Don't remember where I got it, but it was from a search.

 

[Jim F]

Hello all. I thought I would chime in on this subject as I own 2 South Bend 9" lathes and I am familiar with this part.
First, the pin (shoe) on the side of the cross slide (CS) nut does indeed "lock" the nut to the side of the mounting hole. And
by "lock" I mean it applies pressure to the nut to take up any play or movement that would show up as increased backlash.

This shoe is forced out laterally by the top screw, a very small 5/16-24 screw with a 45-degree angle on the bottom. Screwing
down on it forces it to push the shoe outward (the shoe itself has a 45-degree angle. (I will attempt to provide a photo).
These pins are very small and difficult to come by, tho they may show up occasionally on Ebay. A problem that develops is that after
decades of swarf and zero lubrication, the threads on this screw as well as the shoe itself can become quite stuck, resulting in a buggered
up screw slot. So much so that it may be impossible to remove. (I do wish that SB had used an Allen head instead of a straight slot).
I HIGHLY recommend that you replace your cross-slide nuts immediately if you have not done so yet, both on the cross-slide and on the upper compound rest. Backlash will be reduced to a very great extent. But the absolute minimum amount of backlash will only be achieved by replacing both the nuts AND the ACME thread. (a word about that below).

In regards to a nut made of Delrin, I think that yes that is possible, but being plastic, you will not get as much "mileage" out of it as opposed to brass or bronze. I love the machinability of Delrin, but in this case, I don't think the wear factor is a good one. The brass replacement nuts aren't very expensive, so there's really no reason to machine one out of Delrin. If they were a good option, Ebay would be full of them for people to use.

There is a lot more info you need to know about these cross-slide nuts. To help make this post a lot shorter, allow me to recommend a thread I started over on Practical Machinist entitled "9" Cross Feed Nut Replacement". (I cannot post a link here apparently)

There is also something that you can help me with. I have discovered that there is NO hole at the bottom of the vertical shaft that goes into the internal ACME threads on the nut, either on the original nuts made and fitted by S Bend, nor on the new reproductions. Without a small hole, the screw threads get absolutely NO lubrication causing significant premature wear to the mating threads! The way it SHOULD work is that during the course of regular lubrication of your machine, you should unscrew the slotted screw; fill the cavity with oil; work the handle crank to spread and distribute the oil over the entire CS thread (may take more oil as you do this); then re-install the top screw, Be careful not to bear down to the point of buggering the slot!

Where you can help: If you own a SB 9" or 10" lathe (light), and if you have the original nuts in there, I need to know if you have an oil hole that extends into the threads or not. Assuming you can back off the screw, you can test this either by filling the column with oil to see if it drains, or, by inserting a small wire to feel if there is a hole present. I have two original SB nuts and neither of them are drilled! I would like to know if there are more out there like this! This info would be very helpful!!

One last parting word of advice. To the best of my knowledge, there is no way to adequately oil the CS screw without removing the top compound rest assembly...what a pain! The only other way is shooting oil up from the bottom, through the bed "webs" up into a small hole in the casting! It's not supposed to be this hard guys!! So, if/when you do replace the cross-slide nut, be absolutely sure you drill a small 1/8th" hole that extends down into the threads...the repros are not drilled. This is save your CS mechanism from future pre-mature wear.
Again, please thoroughly read the thread at the link above for some tips. (When replacing the nut with a repro, be certain to deburr the hole for the shoe...it must slide freely!)View attachment 351719View attachment 351726

Regards,
PMc

That is not a lube point. That is why there is no hole there.

 

[mcload]

I currently, with the new replacement nut, have about .012 backlash including about .003in the dial end that I can shim out (I hope)

So, maybe I should consider well enough??
Thank you very much for your input.
Very much appreciated.

Dave S.

You are certainly welcome.

I'm not sure what the average backlash number was on new SB lathes from the factory, but I'm
thinking .005 or less. Clearly without a new ACME screw, I'd say .009 or 10 is probably right...but could be better or worse depending on how worn the ACME thread is of course. Replacing that ACME thread is pretty involved, and I'm personally wondering if I should do it myself on my machines. Problem is, you and I can get far too obsessed about a few thousandths of an inch when in all reality, it really won't make a bit of difference with the accuracy of our machines. We're talking about the width of a piece of paper!! (Most people wonder what in the hell is wrong with us!). But I wouldn't blame you in chasing down that backlash either...it's part of the hobby; part of the disease!

But if you've got some time on your hand, it would do a world of good to drill an oil hole in the bottom of that nut to keep the threads from
wearing any quicker.

PMc

 

[mcload]

That is not a lube point. That is why there is no hole there.

Okay, then how and where does the CS thread and nut get lubrication on a 9" and 10" Light lathe? (waiting)