Without question that's one of the off shore generic 918 lathes as Stanstocker has already said. But listing a single dimension of 3/10 is 100% meaningless. Measure the lead screws out side dimension at probably the most unworn area near the tail stock end with at least a good caliper, a micrometer would obviously be far better. Then provide information if it's a left or right hand screw. And if it's an imperial measurement based lathe, what the exact TPI pitch is or in metric if it's a metric lathe. Some of the off shore machines used a mixture of imperial dial markings with metric pitch screws. Maybe of less importance if your replacing both the screw and nut, but you should also identify if the original screw and nut is the proper ACME thread form or in some cases more standard 60 degree threads were used on some of the very cheap and poorly built machines. Your pictures seem to indicate it is ACME, but that also might be really excessive wear I'm seeing. So without any fairly accurate measuring, there's literally no way to be sure of what you have never mind recommend where any replacements might be found. Plus there's issues where the machines components and design were changed during the lifetime of it's production run. Parts produced for a newer or older lathe may or may not be even close to what any earlier or later lathes had.

By the looks of it, the OEM nut was cast iron and almost for sure very poor iron quality at that due to what appears to be a coarse grain structure. And given the lathe way score marks etc, that lathe has had a pretty tough life with poor maintenance and lubrication. So from those indicators it can be assumed the lead screw is also worn well past needing to be replaced. I'd say that today very few of the better machine tool manufacturers now build there own lead & feed screws or the nuts. They go to company's that specialize in producing those items. Even the skill and knowledge to correctly straighten feed screws after machining is a fairly complex process.

If you can't find direct drop in replacement parts? An added bit of back round information is required. Technically using the term lead screw for any slide being moved with a screw & nut is correct because that lead term describes a better degree of screw pitch accuracy and a known movement distance over each full or partial rotation of the screw that matches the dial markings. But that term also creates complications when searching for any replacement screws or nuts because most or maybe all manufacturers use the more descriptive term feed screw and feed nut. And in general, the lead screw and nut term is reserved for the lead screws and half nuts for the lathes longitudinal power feed or during single point threading in something like a user manual. It's still easier and you'll get better results during a search using that feed screw/nut description. Fortunately there are numerous specialty company's that do produce what the OP is looking for. Roton, SKF, Helix Linear are just a few of them. But I don't know who the better known manufacturers would be in the UK. One further issue the OP may face is his lathes lead screw appears to be fairly small in diameter. With those accurate measurements he would have to search through those manufacturer's web sites that give thread diameters, pitches, available screw lengths and nut over size dimensions to see if there even available in the correct diameter, length and pitch. If so? The matching feed nuts are machined by the manufacturer to be well over sized to allow re-machining to fit the required mounting design his lathe or any other machine might have. In the case of half nuts for example, those manufactures would expect any end user to machine the nuts out side diameter round and properly concentric to the internal thread and then soft or hard solder the bronze nut into something like a precision bored steel carrier. At that point you'd then machine the steel to fit the half nuts actuation assembly and then split it in half unless that oversized nut can be machined to fit on it's own. It's fairly involved and accuracy is very important, so only the OP can properly access if he has the required skills to do any of this. If not you'll need to find someone who does. There's at least some manufacturer's who offer machined ends on the feed screw to the correct length and diameters so it at least would be ready to go. That's also really expensive because your paying industrial prices for industrial quality machining and accuracy. But if the lathes head stock through hole is large enough to fit the feed screw diameter, then machining the feed screw to length and diameter on it's plain un-threaded ends could be done using the lathes cross and top slide.

Just in case it's not already obvious to some, any screw pitch and matching nut could be used. But not if you expect the longitudinal feeds and change gear or gear box settings for the correct power feeds or when single pointing a thread. So it's mandatory you accurately match whatever that lathe came with originally. Cast iron material for the nuts can and is used on a number of usually older machines because of the built in quality's cast iron has as a wearing surface. I don't know of any manufacturer using any alloy of brass to machine feed screw nuts from because of it's softness. There's vast difference between brass and bronze alloys, yellow metals despite there appearance are not equal and aren't interchangeable. The lead screws surface finish and environment those half nuts are expected to live in would have a very much reduced life span with any brass I know of. Bronze is chosen instead because of it's much better lifespan outweighs it's higher cost. Replacing both the nut and feed screw also gains you known alloys of each material that have proven to work well over long periods of time. So part of there cost is your paying for the correct materials science and mechanical engineering behind what your buying.

Edited to add, it appears I was mistaken and your instead talking about the cross feed nut. I'll leave it as I wrote it since most of that would still apply to the cross feed screw and nut.

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Construction and assembly of lead screw motors &#; the basics

Adriana Glazer | 20. November

As a well-known manufacturer of engineering plastics, igus has meanwhile established itself in the minds of the engineering universe. But around these core products a huge product world has developed with over 10,000,XXX different products. One of them is the lead screw motor. As the name suggests, a lead screw motor consists of a lead screw and a motor &#; well, and a driven nut, but lead screw nut motor or motor with lead screw and nut sounds rather uncool and is not very marketable. Be that as it may, here and now everything revolves around the construction and assembly of lead screw motors and other things that need to be taken care of.

But what is a lead screw motor?

In its simplest form, an igus lead screw motor consists of a lead screw and a motor. In order to drive something, as a rule, a nut is needed. The whole thing is shown in the following picture.

The motor is designed as a stepper motor with hollow shaft. These motors are specially designed to absorb axial forces. Our NEMA23 lead motor can axially absorb for example 500 N. Conventional stepper motors would be damaged by this axial load. In the hollow shaft there is a holder for our lead screws so that they can be screwed and glued. This connection is so powerful that it can only be released with special tools and a specially developed process.

By the way: please do not try it yourself, the motor can be damaged in 9 out of 10 cases

The motor can also be equipped with an encoder and/or industrial M8 connector. The lead screw has been specially machined for this motor so that the thread starts directly from the motor flange. There is therefore no loss of stroke.

Setting the correct screw straightness

Once the lead screw has been inserted into the motor, the lead screw is straightened. Here we distinguish between two different lead screw motor precision classes (igus in-house misnomer ):

• SMP 0.2               Concentricity of 0.2mm measured from 100mm of the motor flange            
• SMP u                   non-directional without definition

Usually the SMP 0.2 is sufficient, but we are currently working on processes to ensure even better concentricity, but these are not yet fully developed. For very cost-sensitive applications, the SMP u can also be used to offer maximum savings.

Finding the right lead screw length

The definition of lead screw length is somewhat tricky, but nevertheless easy to understand:

• Lead screw length = total length incl. assembly pin and crank
• Unsupported lead screw length = lead screw length from motor flange without assembly pin and crank
• Stroke = unsupported lead screw length minus the length of the nut

In principle, all igus lead screws can be coupled with the motors, but nevertheless &#; as is actually always the case in mechanical engineering &#; common sense should be applied. 40mm lead screw with Nema11 (0.12Nm) certainly looks cool, but nothing more. Since the lead screws require special machining, we have a defined number of lead screw geometries in stock. These are cut to length as required. You can find an overview of available lead screws online or in our data sheet.

yiyuan Product Page

There is nothing special about our nut since it is basically about lead screw motors. Of course, you can also choose a nut from our standard range or request a specified geometry &#; as is usual at igus. We are happy to offer you an injection-moulded special nut according to your wishes and ideas.
The lead screw motors are packed in foam and delivered protected from external influences.

If you are interested in lead screw motors (or lead screw nut motors), please let me know. I will gladly find the right configuration for your application.

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