Since the pitch is 3mm, the thread is certainly going to be metric.

No one in their right mind, in volume manufacturing, is going to cut a 7/8 inch by 3mm pitch ACME thread, are they?

The worrying thing is that the OD varies from 22.1 to 22.25, which would be oversize for a 22mm, and grossly undersize for a 24mm.

Suggestion

The backlash is because the nut is a loose fit on the leadscrew, so why not experiment cutting a nut to 22 x3, and see how it feels? Adjust the O.D. until you are happy with the feel in steel (lubricated – you don't want any pick ups to damage the leadscrew) When you are happy with the fit and feel, for each leadscrew, then make the final version out of your chosen material, (Cast Iron, Brass, Bronze, Phosphor Bronze etc).

It goes without saying to lubricate the screw and new nut well before final assembly.

If you want to minimise backlash, split the nut crossways, and fit a screw to allow you to compress or expand the nut longitudinally to reduce backlash. In future you could use this to compensate for wear.

Howard

I'm neither a user nor owner of one of these particular mills but, surely, if you are intending to replace both lead screw and nut, then it really doesn't matter the exact size of the thread – so long as they match, of course! A quick google search reveals a number of suppliers of ready-made lead screws as well as acme threaded rod up to 40 feet long! Get some of this and turn it down to suit.

Good luck,

John

Hi Paul.

What year is your machine, my VMC dates from 1997 and was made in Taiwan and has table feed screws that measure around 22.2mm. The current slightly heavier built Chinese made versions may have something different.

Regarding the dovetails, certainly on the Taiwanese version they can be a bit of a mess, as well as other mating faces on the head and turret which I have corrected. While the ground finish of the guideways on the column, the underside of the table and the top of the knee of my machine are excellent, its the 'hand finished' surface of those on the vertical face of the knee and the underside of the saddle where the massacre has taken place.

It's clear that the tools used for this brutal butchery on mine range from rough files, angle grinders and a big scraper of some sort. They have dug out a concave surface on the saddle and knee leaving four raised areas and then concentrated on these to get the alignment. It is possible to insert a 20 thou feeler gauge between the slides in places. The poor contact area left by this has led to scuffing and early signs of wear on the nicely ground surface that they mate with.

Despite this, and using much better quality machinery over the years, I have always liked them and it does perform very well in a home workshop. Years ago I visited the Myford works and was shown into one of the back rooms. In here was a new Warco VMC they had been looking over, and they hated it, amongst other things making much of being able to stick the feeler gauges in between the slideways.

Myfords own version of the VMC was a different machine, Warco used to offer an identical type in the 1980's. I think the Myford VMC had just been discontinued, and Malcolm Townsend of Myford recalled to me one of the few problems they once had with it was the manufacturers habit of using a bit of emery tape on a stick of wood that they would ram up the spindle to 'finish' the taper. They quickly put a stop to that.

Edited By Lathejack on 22/01/2014 22:12:37

Paul,

Have you considered replacing the screws with 'ball nuts' and screws which can be obtained at reasonable cost these days, almost zero backlash!

I noticed one of the correspondants suggesting slitting the feedscrew nut. Instead of this consider making a second much thinner nut which is placed at the opposite end of your 'nut carrier' Around the circumference of the thinner nut drill a series of small holes. The nut carrier then has taped holes to match and by careful adjustment backlash can be eliminated. It just means you have to make two feedscrew nuts per axis rather than one, both nuts effectivley working against each other.

IDP