Can anybody tell me what the thread pitch, size and length of an imperial Myford cross slide leadscrew is? I am interested in the longest available length of thread.

Thanks, the 10tpi was what I had hoped, and the link from NDIY is interesting. I generally avoid ebay USA sellers because of the postage and possible duty payable. I suppose the duty would not be payable on the carriage rates. The Atlas 12 x 24 will be staying at the museum because the powers that be got cold feet in case the old Smart & Brown dies with no backup lathe. So I would like to make a new cross slide leadscrew for it. The existing one is 1/2" x 10 LH ACME and because of slightly uneven wear in the leadscrew threads, my antibacklash solution has to be spring loaded. This comprises a new nut combined with the old worn one with a spring between them. Because of the length of both nuts and the fairly short length of thread on the leadscrew, one of the nuts runs of the end of the thread in both directions. Even with a perfect unworn leadscrew, the antibacklash would still have this shortcoming. A new leadscrew could have more thread at each end and still work. The Atlas design of cross slide also leaves much to be desired because of its shortness, If I made a replacement, it would be 2" longer.

Update, I have taken a chance and ordered 24" which includes one nut, total cost £ 44, I hope.

Edited By old mart on 07/05/2023 19:09:50

The leadscrew from the USA is longer and includes a nut for a similar price to the HPC one. This is probably because ACME is still much more common there than trapezoidal. I had not seen their advert before, and after making the slightly longer leadscrew, maybe in two parts, there will be plenty left over which is saleable. I noticed that Tracey Tools have the 1/2 x 10 ACME taps for sale, but the new Atlas nut we already have should fit the new leadscrew and combined with the new one, I will be able to design a superior antibacklash for the cross slide.

As you mention, a quality conventional thread would be a very good substitute leadscrew as even if the pitch error was greater than a dedicated leadscrew. With a cross slide it is normal to measure frequently and only move a short distance at a time which means even an error of 0.005" in the whole stroke, say 5" would only be 0.00025" in 1/4 inch. Of course the usual thread for cross slides is left handed, not so easy to get hold of.

Edited By old mart on 08/05/2023 12:18:16

The round column mill at the museum has leadscrews on the X and Y axes of 2.5mm TR pitch, and only recently was I able to get some er16 inserts in that non preferred pitch, from China.

The leadscrew and nut arrived today, 2 weeks early, and nothing extra to pay over the £44. To improve the lathes poor design, the cross slide is a pathetic 6" long, and also to make installing positive antibacklash much easier, I will be making a longer cross slide, adding at least 2", or maybe more. There is a chunk of metal at the museum which will be used if it is cast iron and the design is very simple.

Edited By old mart on 16/05/2023 14:17:55

Edited By old mart on 16/05/2023 14:19:30