Acorn leadscrew, how would I?

[Jonfb64]

Hi all,

I have an Acorn 42 inch bed lathe (Atlas 10f clone) that could do with a new lead screw. I am considering changing it to metric and the equivalent thread to 8 tpi appears to be 2.5mm. I have looked on ebay and can purchase a length of ready made acme lead screw which would be threaded full length, however the original has a plain part at the head stock and a keyway for the power crossfeed. I am aware I would also have to change/make new half nuts.

My question here to those more knowledgeable than I is would the full length thread matter and how hard would it be to mill the keyway.

Another thought occurred that is I could make my own.

In which case what steel should I use and how do you cut an accurate thread for a leadscrew that is longer than the between centers on your lathe?

I have tried googling but cannot find the answer.

Thanks in advance

Jon

[mfletch]

 I suppose you could weld a bit of over sized round stock on one end then turn it down to the correct size then keyway the end

[Pete.]

10tpi is quite close to 2.5mm pitch. 8TPI is a bit coarser than 3mm.

[krv3000]

hi well this is the way i wood do it turn the end dawn and mack a sleev to go over the top then drill and pin them together  on the compact 8 lathes its dun that way and the pin is soft so if you drive the bed in to the head of the lathe the pin will brack and stop any mager damige if you welld it you my end up destorting the end of the thred

[mfletch]

If its the same as my Atlas there is plenty of thread unused at the headstock end

[Jonfb64]

Thanks for the responses so far.

Any ideas how I would make my own leadscrew ?

I also have a C3 super mini lathe but the bed is a lot shorter so how would I cut such a long thread accurately on it? Would I have to make cuts in sections with an unthreaded portion through the spindle and then when cut move the shaft to the right and continue cutting the next section. Obviously I would need to make bushing to replace the tailstock barrel and support the cut section and allow it to overhang the end of the bed.
Is this way it would have been done in the past?

[Pete.]

I wouldn't think about making a leadscrew let alone in 2 stages. I'd buy acme rod and machine the end. Sleeve it if you have to.