Use the male cross slide screw as a template to make the tool.

Tony

Make yourself a gauge out of sheet metal cut and filed (or surface ground) to either 29 or 30 degrees and see how it fits your old thread.

If you do go deeper, you will need to make your toolbit with a slightly narrower flat on the end, otherwise going deeper will make the thread looser on the angled flanks.

While you have got the top slide to bits, you might be able to incorporate some sort of antibacklash nut system, if there is room.

You have been unlucky with the size and pitch, 12mm TR is normally 3mm pitch, leadscrew material and nuts are easy to come by. I have recently managed to get hold of 2.5 TR inserts, but they are16 size and our leadscrews are about 23mm diameter. I do think that 11 size 2.5 TR are also available from the same Chinese source, but even these small ones would have to be butchered to manage a 12mm thread.

If you went the 3m pitch way, you would have to change the dial engraving, I have done that.

Edited By old mart on 29/07/2022 17:53:38

Just read the opening post again and realised I did the same thread last week but RH for a Kitty planer 12 x 2.5 Trapezoidal — this was a clean up job to free the thread.

Ground the tool freehand using a vernier protractor for the angles, got that correct then reduced the end to make it the right width, the tool holder has been around for years.

Hi Sean,

I am in a similar situation to you, I recently purchased a Boxford STS. The original cross-slide nut/screw had significant wear and the previous owner replaced it with a homemade screw/nut but machined a standard 60 degree 2.5 pitch thread. It seems to do the job quite well but I would like to return it to factory spec if possible.

I too also assumed a TR thread and was about to purchase a TR12x2.5 tap/die set from China until I saw this post.

How did you end up going with this?

Cheers,

Jeremy

Did Boxford really use Brass for the original nuts as per eBay ad?

Tony

.

Given that the ‘Description’ clearly states “Not direct from Boxford but manufactured to the exact same dimensions and specifications.” … One would hope so.

… If not, then Ostia deserves a good thrashing !!

MichaelG.

I saw that one! Yes quite expensive, especially after currency conversion and shipping to New Zealand.

As an engineer I would expect Phosphor Bronze or similar for its wear properties certainly not brass😉

Tony

Rather surprisingly, many manufacturers use brass or even softer metals like Mazak for half nuts and cross slide nuts. They are sacrificial, like brake pads and clutch plates, designed to wear out without damaging the mating part (in theory!). The idea is for all wear to occur on the nut, not the mating feed screw or lead screw.

A worn nut will have a bit of backlash, but will faithfully follow the thread on the leadscrew, and so will cut an accurate thread, or in the case of cross slide will still give an accurate reading on the micrometer collar. But a worn screw will have variable pitch along its length, varying incrementally from the original standard on the unworn bit to the full amount of wear in the middle of the worn section of screw, and then back incrementally to standard again at the other end.

I make my own half nuts and feed screw nuts, all out of brass. I have yet to wear one out in the home workshop. If I were forced to use bronze, I would prefer a leaded bronze. Phosphor bronze is tough/hard stuff and running on unhardened steel shafting usually leads to comparatively rapid wear on the shaft, so I would imagine the same to be true for mild steel screws.