Pultra 17/70 lead screw nut

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

Dell

Member
Joined
Apr 28, 2020
Messages
6
Reaction score
1
Location
UK
I have to find or get made a replacement lead screw nut for my Pultra 17/70 crosslide but I need to determine the thread , the screw measures 6.27mm 0.247” and 20 threads over 1/2” so 40 tpi but all I can find is 1/4” X 40 tpi M/E threads and I wouldn’t think Pultra would have used model engineering threads, the grub screw threads are 6 BA.
Dell
i should have said the dial is 0 to 25 so that points to 1/4” X 40 tpi.
 

Attachments

  • E08FEDF8-BFFD-40AA-9824-890640F71134.jpeg
    E08FEDF8-BFFD-40AA-9824-890640F71134.jpeg
    274.2 KB · Views: 2
  • 66F833EA-36E2-4151-9FFD-ED964150C765.jpeg
    66F833EA-36E2-4151-9FFD-ED964150C765.jpeg
    258.5 KB · Views: 0
Last edited:
Just remember that knowing the lead screws pitch is only half the information. What thread form does that lead screw and nut use? Since I know nothing about those older Pultra lathes it could be ACME or maybe even a more standard 60 degree imperial or 55 Whitworth thread form. And at 1/4" it would be extremely difficult but not completely impossible to single point a new nut. If it is ACME? I don't recall ever seeing any ACME taps for 40 tpi in any diameter, so unless you get amazingly lucky and somehow find something like an original NOS nut your probably looking at a very expensive custom ACME tap or learn how to make your own from scratch. Someone here with decent cnc capability might? be able to thread mill one a bit easier though.
 
Hi Pete
thanks for reply
Well it was definitely 1/4” 40 tpi ME thread , I opened out the hole to 9/32” I couldn’t go any larger otherwise I was in danger of breaking through to other holes turned a bush up to be a very tight fit using a graver ( I couldn’t use the crosslide) ha , pressed it into hole, drilled hole to 5.5mm ,started tapping and promptly turned the bush out so a rethink was in order, as I already had some silver solder paste I cleaned everything up and smeared a small amount of the paste round the bush pressed it back in and heated until solder flowed that did the trick, finished cutting the thread cleaned everything and put crosslide back together, no play whatsoever.
so now to make a new replacement but what metal to use brass or bronze.
also a bit of information that may be of interest
Dell
D162E78F-F1F0-4D5A-8EE1-880158F42436.jpeg

5ED9144C-8DBB-45E6-9E58-00B3C7FC689C.jpeg

C3F9037A-3429-4390-B376-D5FBB2919EE6.jpeg

as I have gout in both hands and struggle to hold the dials and would prefer to have metric dials that are larger , a friend is sending me two dials leadscrews and two pieces nuts, and I think two piece are a much better idea, leadscrew thread is M6 X 1.
143EF197-4398-48AD-856A-A1AC6905179F.jpeg
 
Well the reason for the earlier crosslide only having one single nut is that the leadscrew also screws into the brass part in the centre of the slide, and the later ones don’t hence the 2 part nuts, also the leadscrew nuts on the later metric ones are larger although the are very similar shape, hence the later metric lead screws and nuts won’t fit earlier slides.
Dell
 
Back
Top