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compound backlash/wear (newbie question)

A

Anatol

Aluminum
Joined
Jan 19, 2018
Location
Los Angeles
I'm a new owner of an old 10KL. How would I know if compound screw/nut were (unacceptably) worn?
- amount of slop /backlash when dialing it back and forth? I've got about 50 thou on the dial.
Also - what is the function of the set screw on the top of the compound nut? Is it an oiler and why is it pointy?
thx!
Acompound nut top.jpg
 
Anatol said:
I'm a new owner of an old 10KL. How would I know if compound screw/nut were (unacceptably) worn?
- amount of slop /backlash when dialing it back and forth? I've got about 50 thou on the dial.
Also - what is the function of the set screw on the top of the compound nut? Is it an oiler and why is it pointy?
thx!
AView attachment 321895
Click to expand...

I went to the time and trouble to explain this in your last post.
See reply #18 in joining the 9A brotherhood
Maybe you will believe someone else.

PMc
 
The screw is in the feed nut, but yes the screw is removed to oil feed threads on occasion.

On a South Bend you will always have some backlash on crossfeed and compound nuts. Thats because there is only a single nut per feed screw. Other machines might have two CF nuts that are adjusted to oppose each other, and in turn, remove that slop. South Bends do not have that.

If you feel its excessive you could try replacing the bronze nut to reduce it, but it will never be zero. If the CF screw threads are wore enough, then replacing the screw and nut will also reduce it.
 
texasgunsmith said:
The screw is in the feed nut, but yes the screw is removed to oil feed threads on occasion.
.
Click to expand...

With all due respect, this is not true to my understanding thus far. ONLY 10" heavy and larger models had "thru the screw" oiling capabilities. You will find that
the 9" and 10"L's did not have a direct port (hole) thru the cross-nut for direct oiling of crossfeed screw. I'm sure your 16" (?) does, or I believe you said so.
Why the disparity, I do not know.

PMc
 
mcload said:
With all due respect, this is not true to my understanding thus far. ONLY 10" heavy and larger models had "thru the screw" oiling capabilities. You will find that
the 9" and 10"L's did not have a direct port (hole) thru the cross-nut for direct oiling of crossfeed screw. I'm sure your 16" (?) does, or I believe you said so.
Why the disparity, I do not know.

PMc
Click to expand...

I found this on an internet search. It was for a cross thread nut cover (at auction site) that clearly has the world "oil" stamped on it. the text reads

"South Bend Lathe Cross Feed Screw Nut Screw NOS. You are buying a new old stock South Bend lathe cross feed screw nut screw. It has the set screw that you remove to oil the nut. I don't know what this fits, but it may be for the heavy 10. It is in good condition. See pictures for condition and dimensions. This came from the factory at South Bend Lathe maintenance room. We bought the contents of the room at one of their auctions."

So at least this item listing proves the 10" heavy issue I mentioned. Would be nice if some owners of 10L's and 10H's could confirm if this port cover is present or not. Why does this seem to be a mystery?:nutter:

PMc


View attachment 321907
 
mcload said:
With all due respect, this is not true to my understanding thus far. ONLY 10" heavy and larger models had "thru the screw" oiling capabilities. You will find that
the 9" and 10"L's did not have a direct port (hole) thru the cross-nut for direct oiling of crossfeed screw. I'm sure your 16" (?) does, or I believe you said so.
Why the disparity, I do not know.

PMc
Click to expand...

Now that you mentioned it. I seem to recall a thread a while back, and it was you if i recall. . .:D

The thread in question dealt with new CF nuts that were not drilled all the way thru. Style of nut a bit different, as i recall. But with a minor mod hole was drilled thru to allow oiling. Not sure op's situation here, but if not drilled thru i would guess it can be done.
 
Thanks everyone and sorry for confusing the issue by saying compound when I should have said crossfeed. :(

Texasgunsmith - I get that there will always be some slop/backlash. What I'd like to get a sense of is how much slop are folks willing to live with before it justifies a new nut? (As noted, I have ~50 thou). How much slop is there with an as-new crossfeed thread/nut?

Yes, I've seen machines with a double nut that can be adjusted to fix backlash. It's a good idea, I wonder if anyone has made one for a 9A/10K?

PMc - yes we talked about this in another thread, and I'm grateful for you advice and thanks for your patience. You said you drilled an oiler hole. That seems to suggest the nut on your machine does not have the grub-screw.
My question now is about the grub screw in the top of the crossfeed nut, a pictured. If its not an oiler, what is it? And why is it pointy?

Sparky - yes, next time I'm in proximity of the machine, I'll pull the thing apart again and see if the hole goes through. (That question was kind of a footnote to the slop question).
thanks all
A
 
Anatol said:
T... How much slop is there with an as-new crossfeed thread/nut?
...
Click to expand...

You separate out the lash from the nut versus the lash from the screw:

Measure the lash at the center of travel. Then measure it at the extremes of travel, where the nut rarely rides - that will be less.

The second, smaller number will be close to the value for the nut alone. Subtract the smaller number from the larger, that's about the maximum wear in the screw.

Long story short, the wear in the nut and the wear in the screw are going to be about equal in most cases. If you want the best performance:

1) be sure the dial-to-bushing clearance is minimal (dial does not not back away from the bushing during infeed).

2) replace the worn nut with a new one.

3) install a new piece of precision acme rod on the crossfeed shaft.

Parts like this are sold by members here.
 
What exactly do you mean by 'pointy'?

Looks like an ordinary grub screw to me. They're all over the place plugging oil passages on old machines. My 13 has probably got 3 or 4 of them and my horizontal mill has somewhere around half a dozen.

I don't know why there would be a screw there if it weren't plugging an oil passage. There would have been no conceivable point in South Bend drilling and tapping a blind hole in a crossfeed nut only to plug it with a grub screw. Would've been a complete waste of time and money. And besides - how else would you be expected to lube the crossfeed nut? Tear the whole saddle apart on a regular basis?

It's an oil passage. It's got to be unless someone was asleep on the job that day.
 
The reason for the "pointy" looking screw in the top of the cross feed screw nut on the 9" SBL is, that it pushes against a round pin that is cut on an angle on one end and slightly spherical on the other end. This pin is inserted into a cross drilled hole in the .625" dia. shank portion of the nut. The wedge end goes in the hole first and is oriented so cone point set screw goes against the wedge of the pin. The spherical end of the pin, when pushed outward by the tightening of the set screw, forces the spherical end against the bore of the cross slide which locks the nut from moving. That is it. It is not an oiling point for the nut on the 9" SBL. I guess if you wanted, you could modify things provide a point of oiling. Problem is, you will defeat the original purpose of the cone point screw and the wedge.

All the 50 plus years of using my 9" SBL, I've always moved the cross slide all the way off the nut, to the back end of the cross slide. Cleaned the dovetails, applied oil the the screw for the full length and also to the dovetail ways and retracted the cross slide to it normal position on the saddle. Don't take but a minute or so to do this. Also part of doing proper maintenance in maintaining your lathe in tip top shape! Oh, my lathe has about .010" slop in the cross slide nut and between the collar and dial. The last time I tried to remove some of the slop has been many years ago. IT's about time to trim things a little to remove some of the slop. As for making a compensating nut for the cross slide, I see not need for one for my lathe. Ken
 
im replacing mine currently, it has about 0.038" of wear/play to it. So far my costs are about $200 for an acme tap, $90 in material and $200 for a machine shop to machine me a new acme thread/ cross slide screw assembly. found a bunch of other hack job goodies while i was in there and found a can of worms........ like you always do. doesn't take long to drop thousands in time and labor rebuilding a machine.
 
Anatol said:
Thanks everyone and sorry for confusing the issue by saying compound when I should have said crossfeed. :(

Texasgunsmith - I get that there will always be some slop/backlash. What I'd like to get a sense of is how much slop are folks willing to live with before it justifies a new nut? (As noted, I have ~50 thou). How much slop is there with an as-new crossfeed thread/nut?

Yes, I've seen machines with a double nut that can be adjusted to fix backlash. It's a good idea, I wonder if anyone has made one for a 9A/10K?

PMc - yes we talked about this in another thread, and I'm grateful for you advice and thanks for your patience. You said you drilled an oiler hole. That seems to suggest the nut on your machine does not have the grub-screw.
My question now is about the grub screw in the top of the crossfeed nut, a pictured. If its not an oiler, what is it? And why is it pointy?

A
Click to expand...

Pointy? and thats a 710 hole just flip it around 180 degrees :P
 
Back to the backlash question. Where is the backlash occurring? Is it from the crossfeed nut, or is it from a lack of shimming washers/spacers in the leadscrew?


One mod that I would do NOW, is drill the thru hole that was discussed in the other thread to allow oiling of the crossfeed screw. Seems like a "no-brainer" to me.
 
"What exactly do you mean by 'pointy'?"
I meant the end opposite the head is ground to a ~60 deg point. Most set screws I've seen have a 'dimple' in the head.
"I don't know why there would be a screw there if it weren't plugging an oil passage."
Y'd think so, but a member in another thread was emphatic that a design error that SB never addressed was that the was no oiler for the crossfeed nut, and he strongly advised drilling one. He was referring to a 9A, so maybe SB did address this on the 10K. I understand that one of the design differences between 9A and 10K is 10K has a different, beefier saddle.
A
 
4GSR said:
The reason for the "pointy" looking screw in the top of the cross feed screw nut on the 9" SBL is, that it pushes against a round pin that is cut on an angle on one end and slightly spherical on the other end. This pin is inserted into a cross drilled hole in the .625" dia. shank portion of the nut. The wedge end goes in the hole first and is oriented so cone point set screw goes against the wedge of the pin. The spherical end of the pin, when pushed outward by the tightening of the set screw, forces the spherical end against the bore of the cross slide which locks the nut from moving. That is it. It is not an oiling point for the nut on the 9" SBL. I guess if you wanted, you could modify things provide a point of oiling. Problem is, you will defeat the original purpose of the cone point screw and the wedge.

All the 50 plus years of using my 9" SBL, I've always moved the cross slide all the way off the nut, to the back end of the cross slide. Cleaned the dovetails, applied oil the the screw for the full length and also to the dovetail ways and retracted the cross slide to it normal position on the saddle. Don't take but a minute or so to do this. Also part of doing proper maintenance in maintaining your lathe in tip top shape! Oh, my lathe has about .010" slop in the cross slide nut and between the collar and dial. The last time I tried to remove some of the slop has been many years ago. IT's about time to trim things a little to remove some of the slop. As for making a compensating nut for the cross slide, I see not need for one for my lathe. Ken
Click to expand...

Thankyou very much for a clear and thorough explanation for the mysterious pointy grub screw. I'd seen the pin sticking into the hole and had wondered.
So... if the side face of the point is the bit doing the work, would it be abad idea to drill a 1/16 hole in the bottom of the thread well to allow oiling by removing the screw?
Thanks also for info on slop.
A
 
"Where is the backlash occurring?"
good point, I need to establish that. I'm guessing in both places, but shims will no doubt help.
BTW, I made a slotted driver for the little dome nut on the end of the compound and crossfeed handles - out of a broken 1/2" spade bit. Used a cutoff wheel in a die grinder. Its not pristine but it works and a whole lot better than the last guy's attempt with, presumably a small cold chisel, he mashed it up good, so I've cleaned up the slot some. Works and looks better now.
A
 
Anatol said:
.................................., would it be abad idea to drill a 1/16 hole in the bottom of the thread well to allow oiling by removing the screw?
Thanks also for info on slop.
A
Click to expand...

I guess if you wanted to do so. My SBL was born in 1949. Of that time, a oil hole was not part of the design. Maybe later SBL added it to the nut. IDK. BUT, if you drilled a hole there, how are you going to keep crap from getting in the hole and eventually getting into the threads and screwing them up? The smaller lathes were not designed with oiling points as larger lathes are equipped with. So a lot of manual oiling by moving slides around to get to the screws is the only way to get oil to those areas. It's never bothered me to move the cross slide the back side of the lathe to oil things. Most of the time, when I do this, I do a "quick" cleaning with a clean rag to the ways and apply oil. Just takes a couple of minutes to do. Don't need to tear down the cross slide to do this.

On my 14" Rockwell lathe when I rebuilt it, I made a new cross feed nut and screw, and added a Gits oil cut to the top of the nut for oiling.

Ken
 
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