Acceptable feed screw backlash

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Acceptable feed screw backlash

This topic has 9 replies, 9 voices, and was last updated 15 April 2025 at 20:31 by old mart.

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14 April 2025 at 19:17 #793319
david newman 9
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@davidnewman9
I have a tom senior e type and it seems to have had very little use, but it has 20 thou backlash on both axis would this have left the factory like this and is it acceptable ? By the look of the machine I am sure it is not wear as it looks to have been well cared for and as I said little used. Thank you David
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14 April 2025 at 21:26 #793343
Bazyle
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@bazyle
You will need to dig a little deeper to see where the slack is. We had a similar thread a few days ago wrt a lathe cross slide. Probably just adjustments or loose screws during transport.
Possibilities are around the handwheel and bracket at the end of the table – does is move in out without being turned?
The nut attachment to the table – loose screws.
The nut backlash adjustment – it probably has some method and agin might have come loose in transport.
14 April 2025 at 21:35 #793344
Dave S
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@daves59043
I have something like 1/4 of a turn backlash on my mill.

Not an issue for actual making of things, especially with a DRO
14 April 2025 at 22:49 #793346
Fulmen
Participant
@fulmen
Finding and reducing backlash is a great exercise in machine maintenance. But within reason it’s only a slight nuisance and since it can’t be eliminated completely there is no reason to panic. A few tests with an indicator should tell you if it’s repeatable, that’s all that really matters. You have to take up the slack no matter what.
14 April 2025 at 23:26 #793352
Paul Lousick
Participant
@paullousick59116
All lathes have some clearance in the leadscrew (unless it is fitted with ball nuts with anti backlash as used on CNC machines), otherwise they would be difficult to turn. Many have a split leadscrew nut that can be adjusted.

Slop in the leadscrew is only an annoyance and precision work can still be done if you only set the distance by turning the dial in one direction. If you overshoot the mark, retract the slide and advance again.
15 April 2025 at 07:36 #793360
halfnut
Participant
@halfnut
A lot of backlash occurs where the graduated dial or handwheel is mounted on the end of the feed screw. In most cases it can be reduced or eliminated by adjusting the nuts or whatever that hold the dial/handle in place.
15 April 2025 at 09:43 #793376
SillyOldDuffer
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@sillyoldduffer
On 14 April 2025 at 19:17 david newman 9 Said:

I have a tom senior e type and it seems to have had very little use, but it has 20 thou backlash on both axis would this have left the factory like this and is it acceptable ? …

It wouldn’t have left the factory like that – new machines are adjusted by the maker to minimise backlash. But they don’t stay perfectly adjusted for long because the usual anti-backlash mechanism isn’t perfect. Rather a compromise that does the job cheaply, with an easily replaced nut when it wears out. (Assuming a spare can be found for a machine long out of production! If you need to make one, ask – several alternatives. Replacing a lead-screw is more difficult.)

Paul’s picture shows a typical anti-backlash arrangement. A slot is cut part way through a brass or bronze nut, and a screw, not visible, is used to open or close the slot. Bending the nut at the slot causes its thread to grip the lead-screw more tightly.

Sadly, nut squeezing causes severe wear, even if the lead-screw is well oiled. Therefore, avoid obsessively minimising backlash as it can take years off the life of the nut and the lead-screw.

And there’s no need to fuss! The operator can and should compensate for backlash on a manual machine. The usual tactic is to leave backlash unadjusted until handle turning to compensate becomes excessive. For me somewhere between 120° and 200°.

Also, check Bazlye’s list of other causes before messing with the slot!

Dave
15 April 2025 at 14:00 #793405
Dave Halford
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@davehalford22513
It’s 40 odd years old and someone will have fiddled with it by now. It’s also entirely possible that it has not be re assembled properly.

Halfnuts solution is the most likely fix.
15 April 2025 at 16:00 #793415
Fulmen
Participant
@fulmen
On 15 April 2025 at 09:43 SillyOldDuffer Said:

Sadly, nut squeezing causes severe wear

That’s always good advice 🙂
15 April 2025 at 20:31 #793432
old mart
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@oldmart
First, try measuring the backlash close to the full travel in either end and compare it with the centre figures. The original bronze nuts had no backlash adjustment from the factory. Don’t forget, any end play in the leadscrews will add to the backlash. I made modifications to the museum’s Light Vertical in both the X and Y axes with custom made antibacklash nuts. Rather more than most people would undertake, we had another mill to help as well as a lathe.
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