[fomaz]

Hello. I am trying to repair a large machine 14000 pounds that is in good mechanical condition except the backlash that it presents on the X and Y axis.
The backlash is constant for all the travel so I am hopefull that I can eliminate the backlash on the nut.
Nut is double type that I think is made for this propose - to eliminate backlash.

I have attached 3 photos. I do not know if the nut can be safely opened from the center, and I also do not know if the black covers at the end (that have angular slots) are meant to be loose.

Any information is welcome as I do not want to damage the nuts.
Thank you

[the_gentlegiant]

Hi Fomaz,

I'm 99% sure those things on the end are just wipers and have nothing to do with backlash or screw adjustment. That is usually done by changing the bearing ball sizes inside the nut and/or changing the thickness of that spacer in the middle that is held in with that screwed in plate your arrow points at. This is a time consuming and touchy job that takes a little experience to take on. How much backlash are you talking about? Perhaps the backlash compensation setting in the control is set incorrectly. I'd check that out first. Unless the machine is always used at full travel capacity, which is rare, a screw is seldom worn evenly along it's full length.

[fomaz]

The backlash can be felt by hand so it is too much (one hand in the screw and the other on the nut).
I agreed that is strange that the backlash is almost constant, and I am sure that the support bearings are ok, so it is really on the nut/screw.

[fomaz]

I was the last hour inside the machine but it payed off.
I removed the screw and the two nuts disengaged without any ball lost. Thigh them up against each other until the preload is ok. Now is time to make another locking, this time with a offset and I think that the job is done!

Thanks again.

[the_gentlegiant]

That's one way to do it. Good luck with that. Don't forget to re-evaluate the backlash compensation in the control when you get it put back together.

[handlewanker]

Hi.......if you remove the key that holds the tow nuts together and measure the gap between the faces of the nuts with a feeler gauge you should be able to fit a shim between the faces and then refit the key.

All the key is doing is stopping the second nut from turning and getting loose or tight etc.

You need to have the key in the nuts but as the key was fitted to new nuts when they were butted face to face at the preload setting...... now the nuts are slack they need/can be retightened by moving them away from each other and that is where the shim comes in.

When you think the preload is right the keyways must be exactly in line to enable the key to be re-inserted.

Test the condition of the screw once you have corrected the preload by running the coupled nuts up to each end.....it will probably go tight past the centre point.......if this happens the screw is worn in the middle, so you "could" use a slightly thinner shim to allow the full screw travel, but in most cases the middle part is more important than the ends, but homing where the table moves to the end of it's travel will cause a problem if the nuts are too tight.
Ian.

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