The atlas cross slide has been replaced with a better design and now has 0.001" backlash. However, the top slide is not great and I cannot use the unused part of the 1/2 X 10 ACME leadscrew because it is LH and top slides use RH. Making a 1/2 x 10 ACME nut would cost at least £42 for the tap, so I will be making a replaccement leadscrew and nut tomorrow on the Smart & Brown model A. There is a problem with the thread size, namely the core diameter of the nut which would have to be 0.3" for a 10 tpi thread. That means that to singlepoint, the tooling would have to be very slender, even if an insert was silver soldered into a Densimet (tungsten sintered alloy) shaft. After checking the clearances for leadscrew and nut, I decided on an easier option. When making thread on a lathe, they can be any size you want, the threads only have to fit together. I decided on an 0.7" leadscrew which would make tooling much easier to make. There was a glitch when I found that the S & B was turning a taper between the chuck and the tailstock live centre. My new Indian test bar between centres was needed to re align the tailstock to 0.0005" in 12". And there is no change over the full tailstock stroke. There is zero dti movement when the bar is rotated between centres at either end and in the middle, I'm very pleased with it. After correcting the lathe, I ended up with a shaft of 0.691" which will do fine. The core diameter will be about 0.491" which is much easier to thread.

The start bore should read 0.591", not 0.491" I have threaded the nut, but have yet to match the leadscrew to it. Removing the job from the lathe part way through may seem a bad idea when threading, but as long as backlash in the drive chain is taken out first, it is easy to pick up the thread. The nut was threaded using a left hand tool with the spindle in reverse.