Remove play in internal square thread

Hi,

I am restoring an old lathe and have got to the cross slide.
There is play in the handle I turn to move the cross slide. I can turn the handle about a sixth of a turn with the slide not moving.

The handle is attached to a rod with a square thread.
The rod screws onto a hole that has a matching square thread.
The problem is with the thread in the hole (The rod is OK).

It looks like someone has fixed/bodged this before with a heli-coil type of square thread insert. You can see it in the pic below.

When is the best/correct way to repair this and remove all play.
Bear in mind I am a novice engineer and if a lathe is needed I do not have one until this project is finished.

Thanks in advance for any advice

I wouldn't worry too much about this. A bit of backlash on the cross slide feedscrew will not affect how well the lathe turns, as long as the gibs are correctly adjusted. I use my old Drummond Flagellator with more backlash than that and it will turn to tolerances of less than a thou.

If at some point in the future if you feel it absolutely necessary to tighten it up a bit, there are several ways to do it. Using the lathe as it is now, you could turn up a threaded insert and loctite it into position in the hole where the thread goes in the lathe saddle. This would require some tricky setting up in a milling machine to bore the hole true and straight before fitting the insert. Can't see from your pic, but you may be able to knock out the existing insert, if there is one, and simply instal the replacement.

Square thread taps are available from Tracy Tools and others to make the internal thread in the insert.

An easier but more expensive way might be to buy a readily available Myford feedcrew and matching nut. Their nut is held in position by a flat flange and two small screws, so the lathe saddle could be modified to accept it by setting up in a common drill press. Or make your own insert in the style of the Myford part and attach it with two screws. It's basically a top-hat shape with part of the "brim" of the top hat cut away to clear the cross slide body.

What make and model of lathe is it you are restoring?

Edited By Hopper on 19/11/2018 22:43:29

I can turn the handle about a sixth of a turn with the slide not moving

Not a problem

Start cutting metal ASAP

Lathework is like sex

You can read as many books as you like and make all sorts of improvements

But if you want to get any good at it you've just got to do it a lot

The lathe is an old Zyto.

I'm a bit OCD and now I've fixed the play in the headstock bearings the only place with play is the cross-slide screw so I assumed it would need sorting.

I'm a complete lathe novice and have not used one for 35 years so I will listen to what I'm sure is your experienced advice and leave it as is for now.

I've got loads to learn once the lathe is ready to use

It's good to know lathework is like sex. It means I should be very good at it

Operating a lathe usually only needs one person.

Mike

You could white metal the nut, this will remove the back lash and will last long enough to make a new nut.

Nearly everyone lives with some backlash - only those with special anti-backlsh nuts etc avoid it. The acid test is whether the backlash is consistent along the length of the screw feed.

If the backlash is markedly less at the extremites of travel, the lead screw is worn in the middle part. If the same, and loose all the way along, the nut is worn. Adjusting gibs, properly, will indicate a worn slideway or not. A worn slideway will never be corrected by renewing the leadscrew and/or nut.

Ady1,

Do you think I might be a bit old,at 80,to try one or the other ??

Just asking !!

Hello Jim,

If my memory is correct, Zyto lathes were clones of the old Myford ML4 and details such as the female threads for the square threads on the tool slides were cut directly into the static members without nut inserts being used.

I would do as Hopper suggests and use the lathe as it is, a degree of backlash of that order is not severe and is really just a minor wart in an old machine that you will get used to.

Regards

Brian

My 1908 Drummond suffers from crosslide backlash but I wind the tool in to where I want it and then lock the crosslide whilst I traverse the cut. This system works well for me. A down side is that it is difficult to use the dial on the handles so I fitted a cheap home programmed DRO ( approx £25.00) just on the crosslide. JC