Acceptable feed screw backlash

[david newman 9Participant @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

[BazyleParticipant @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.

[Dave SParticipant @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

[FulmenParticipant @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.

[Paul LousickParticipant @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.

[halfnutParticipant @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.

 

[david newman 9]

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

[Dave HalfordParticipant @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.

[SillyOldDuffer]

On SillyOldDuffer Said:

 

Sadly, nut squeezing causes severe wear

That’s always good advice 🙂

[old martParticipant @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.

[PeteParticipant @pete41194]

As others have said, I’d take it apart and investigate if there’s mechanical reasons, loose or incorrectly assembled parts. Just lay them out in there correct orientation to how and where you remove them from. And by now it very likely needs taking apart for a proper cleaning & re-lubrication anyway. You might be surprised about just how filthy it is. Any evidence of black oil is a sure indicator that it’s contaminated and only helping to further increase the wear.

Something like a can of electrical contact cleaner spray works well for flushing the parts and those feed nuts clean. If there’s no mechanical reasons and method of adjusting the nut, .020″ if it’s caused by wear on a machine of that age isn’t too bad at all David. For perspective, even a brand new Bridgeport is only guaranteed to not have more than .004″ of X,Y backlash.

Yes the manufacturers do adjust new machines, but my own BP clone had the gibs and feed screw adjustments done to allow for the usual anti rust preservative on all the surfaces during storage and shipping. Cleaning all that off while having the X and Y axis apart, a re-lubrication, adjustments to the gibs and nuts reduced that by just about half while still having a far smoother to operate, but much tighter machine. Unfortunately that all has to be done using some caution and feel about how much is enough, but not too tight. That ‘feel’ isn’t easy to describe. Minimal clearances, but still no trace of tightness anywhere over any slides and feed screws full travel is the best way I can explain it.

[Speedy Builder5Participant @speedybuilder5]

The problem with backlash is when you are climb milling and the cutter grabs more material than it should.

bob

[old martParticipant @oldmart]

Checking endfloat on the leadscrews is straightforward. Remove the winding handles, slacken off the lock for the 200 division dial and slide off. There may be a little brass pad under the locking screw,so try not to lose it. The adjusters are then revealed. Some home made spanners or a little punch used carefully will remove any endfloat, but take care not to overtighten as the thrust bearings will suffer.

[Graham MeekParticipant @grahammeek88282]

Acceptable backlash in my book is from 0.05 to 0.1 mm. I have always set my machines to these figures and have found I rarely have to re-adjust the backlash until a couple of years later.

One point which has not been touched upon is that too much backlash not only has the chance to cause an accident as pointed out by Speedy Builder5, but the excessive clearance allows a greater chance of larger pieces of Debris into the nut. This I don’t really need to point out will only accelerate the wear. Which in all probability will be to the feedscrew as the softer nut now acts like a Lap.

Regards

Gray,

[Author]

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