Which method to reduce cross-slide backlash?

tobnpr · Oct 16, 2019

About 1/2 turn (60 thou) backlash on a Sheldon I've just brought "online".
The screw shows light/reasonable wear on visual inspection, and backlash is about the same even at the far end of travel where there would be zero wear; so the bulk is in the nut.

Machine a new bronze nut? No acme threading tooling or tap, easily solved. Delrin? Even seen this "melted" around an unworn section of screw after boring to correct ID as alternative to machining.

Moglice? Perhaps impractical for such a small job (my guess is I'd have to buy far more than needed for such a small job and I'm sure it ain't cheap). But time is money, and the far end of the screw (integral taper attachment) never sees the nut so it is unworn and perfect to "cast".

I've also heard of using solder inside the nut threads to reduce backlash.

What's the fastest/easiest route here?

HuFlungDung · Oct 16, 2019

Check the actual end play of the screw against it's thrust housing. Perhaps a custom shim washer will tighten it up considerably. If you can get it down to .030" I wouldn't bother with trying to reduce it further. I use large manual lathes all day long with .015" to .030" radial backlash, and it doesn't bother me a bit. Mind you, the screws are coarse, so that doesn't amount to a half turn, more like a quarter turn.

Excessive backlash really only becomes a problem when you're trying to back out quick near a shoulder when threading. Then it is nice to not have to turn it so far to get clear. But you always have to learn to compensate for backlash when running any manual machine with acme screws by making your cutting position with a uni-directional positioning move.

Cole2534 · Oct 16, 2019

I put a delrin nut in my monarch when I redid the x slide screw years ago. It's easy, it's accurate, but...it sucks for knurling. The high tool pressures and plastic nut make getting a good knurl tedious.

I can't say that I'd recommend it on a lathe of that size. And one day I'll eventually replace mine with bronze.

Sent from my SM-T560NU using Tapatalk

naru · Oct 16, 2019

What thread is your screw and nut? I’ve got quite a few acme taps, I may be able to thread something for you if needed.

Or if the screw and nut are both worn I’d be happy to make you a replacement.

metlcutr55 · Oct 17, 2019

google anti backlash nut

Gordon Heaton · Oct 17, 2019

My Sheldon (1975 EM-70) has a split nut with the ability to adjust for backlash. Have you had yours apart to see if you have it too?

D Nelson · Oct 17, 2019

Could a guy install a gas cylinder off a car a small one to push back against the toolpost to remove the back lash. Kind of like holding back against it with the off hand?

Sent from my iPhone using Tapatalk Pro

naru · Oct 17, 2019

I suppose you could do that. But with a cylinder causing constant pressure on one side of the thread profile at all times I’d expect some expedited wear. Pressure on the screw during a cut is one thing but pressure on the screw and nut constantly is another. Also depending on the amount of wear the screw has any inaccuracies would be more apparent I would think. IMO. I just make a habit of giving by toolpost a quick tug back towards myself before making my adjustments. But that’s more to do with endplay really, though backlash would cause that as well.

tobnpr · Oct 17, 2019

naru said:
What thread is your screw and nut? I’ve got quite a few acme taps, I may be able to thread something for you if needed.

Or if the screw and nut are both worn I’d be happy to make you a replacement.

1/2"- 8 tpi.

If there's a tap made for it (not going custom for a one-off), I can't find one.

I do have an internal threading tool for TNMV "standup" inserts but can't find an acme insert that size.

Solid carbide cutter runs over $100. Search continues...

MrWhoopee · Oct 17, 2019

How far have you dug into this? My SB Heavy 10L had 140 thou (!) of backlash when I got it. Tightening up the bolt that retains the nut got rid of most of it, replacing the missing thrust bearing eliminated the rest. It now has less than 10 thou. Sometimes it's simpler and easier than it seems.

naru · Oct 17, 2019

tobnpr said:
1/2"- 8 tpi.

If there's a tap made for it (not going custom for a one-off), I can't find one.

I do have an internal threading tool for TNMV "standup" inserts but can't find an acme insert that size.

Solid carbide cutter runs over $100. Search continues...

I may actually have one of those.. if not threadmilling is a viable option. You’d be hard pressed to single point that. The minimum dia. Of that thread must be around .4-.38”.

MrWhoopee · Oct 17, 2019

Buy a nut

Acme Sleeve Nut, 1/2 - 8, LH, Bronze - Roton Products, Inc.

9100 · Oct 18, 2019

These people probably have the original part. If it is not impossibly expensive, pay the price and get the right part.

Sheldon Lathe OEM Repair Parts by Bourn & Koch

The Cincinnati cylindrical grinders I work on have a hydraulic cylinder on the cross slide that takes up the play when running. They routinely work to tenths.

Bill

Cole2534 · Oct 18, 2019

MrWhoopee said:
Buy a nut

Acme Sleeve Nut, 1/2 - 8, LH, Bronze - Roton Products, Inc.

This ^^^^^ is definitely the way to go.

Peter Colman · Oct 18, 2019

Want a crude, low tec, nothing to loose type solution? Then get the nut in a vice and very carefully squeeze it until it is just right on the screw.
I know it's crude but but it works rather well!

Gordon Heaton · Oct 18, 2019

9100 said:
These people probably have the original part. If it is not impossibly expensive. . .

Bill

Just to prepare anyone going this route, last month I asked them about a replacement fwd tumbler gear: one fiber gear and the associated bushing. The quote? $975! Yup, no typo. Nine hundred and seventy-five dollars for a 2" formica gear and a bushing. Unbelievable. I used a $30 standard from Boston Gear instead.

CarbideBob · Oct 18, 2019

Why?
You cut inwards not outwards.
You need to face groove to a certain spot , go into it.
There will always be some lash so is .003 better than a 10 or 30 times bunch?
Maybe some could speak to .002 lash vs .060.
Bob

Gordon Heaton · Oct 18, 2019

Generally right, Bob, but it does get annoying if backlash is excessive. Any more than my wrist will turn without changing grip is too much, or even less than that when backing off a tight bore. You know... is it clear yet? etc.

MrWhoopee · Oct 19, 2019

CarbideBob said:
Why?
You cut inwards not outwards.
You need to face groove to a certain spot , go into it.
There will always be some lash so is .003 better than a 10 or 30 times bunch?
Maybe some could speak to .002 lash vs .060.
Bob

Backlash is just generally at odds with the perfectionist nature of machinists. It is sloppiness that exceeds our level of psychological tolerance, which is in the tenths. The minimum amount of backlash on a lathe is barely tolerable. The fact that quality, precision work is possible with backlash in the .06 range is irrelevant. It upsets our mental balance like a window out of plumb.

thermite · Oct 19, 2019

Cole2534 said:
I put a delrin nut in my monarch when I redid the x slide screw years ago. It's easy, it's accurate, but...it sucks for knurling. The high tool pressures and plastic nut make getting a good knurl tedious.

I can't say that I'd recommend it on a lathe of that size. And one day I'll eventually replace mine with bronze.

THANK YOU! ....for that ration of honesty off the back of actual field experience.

"Some folks" were of the opinion that Delrin was actually all-around BETTER than bronze. Neither are perfect, of course, but still.

There ARE sources for bronze nuts to modify, and one can also then split them or pair them for backlash adjustment.

Not as if a body was likely to have to do this TWICE, any given machine-tool, what with how long the originals lasted in what was probably more severe service and greater neglect than we ever-so attentive chikn's plan to lavish on our toys, going forward. Or - realistically - just use them less-often?

Which method to reduce cross-slide backlash?

Hot Rolled

Diamond

Diamond

Aluminum

Cast Iron

Titanium

Stainless

Aluminum

Hot Rolled

Hot Rolled

Aluminum

Hot Rolled

Diamond

Diamond

Stainless

Titanium

Diamond

Titanium

Hot Rolled

Diamond

Similar threads