Nowt to add to the material choice but I would make a feed screw as a square thread – particularly if a new nut was required at the same time. I see no advantage of a trapezoidal thread in this application. Both my Raglan lathe and mill were fitted with square threaded feed screws as OE.

So much easier to make a cutter to do the job.

I like EN8DN for screws. it's free-machining EN8.

Edited By Pete Rimmer on 02/10/2019 10:24:15

I'm not sure a square thread is easy to arrange with a split-nut attach & release system. Of course, yours might be different. But remember that square threads were abandoned long ago as sodding difficult to machine …

Cheers, Tim

Richard, it is easy and very cheap to buy off the shelf. I bought a 1 metre length of 16 x 4 l/h plus nuts. enough for three leadscrews around £60

Richard, that thread of yours looks like ACME or trapezoidal, (29 or 30 degree angle), not square. If it is imperial pitch, it is ACME, and if it is metric pitch it is trapezoidal.

Chris Evans mentions that 16 X 4 TR leadscrews and nuts are easy to get hold of, this would be the easiest option, just a little machining of the ends needed. And an opportunity to incorporate antibacklash if there is room to do so. 

Edited By old mart on 02/10/2019 19:18:27

I bought mine from Automotion Components and bought two nuts thinking the wear would be rapid. Four or five years on there is no sign of requiring the fitting of the spare screw and nut. The lathe is used around three hours a day about four times a week Look at the position and design of your machines nut to see if it can be split to move apart for backlash. Some Colchester lathes use a wedge pushed into the split nut by a grub screw.

I read this thread as a mis-named feed screw, not a lead screw. It is certainly ambiguous and with the word ‘cross’ included, to me, indicated he actually meant feed screw for the cross slide – not the lathe lead screw. Also, can someone please explain exactly how any feed nut, on its own, is “adjustable for wear”. As I see it backlash simply increases as wear takes place until unacceptable or the nut threads fail.  Half nuts should be adjustable, to a point, obviously.

I can clearly understand the need for a non-square thread for a lead screw, but not for a simple feed screw. Square is stronger than alternatives, cutters are simplicity to make (and it matters not a jot if slightly too narrow as the thread can be corrected by the odd division or two on the compound slide).

Edited By not done it yet on 03/10/2019 19:35:50