Ed,
You can determine the thread pitch easily by how many thousandths of an inch the dial moves the slide in one rotation, as long as it's direct to the screw and not geared.
As for the mounting, it might be a wise idea to re-engineer the whole thing and get the nut mounted securely with two socket head cap screws from the top side and a cone point set screw between them to adjust/spread the split in the nut to reduce backlash. That's how my lathe is designed and it works perfect (once I get that special lockwasher.)
I'd be willing to make you a new screw and nut, so all you'd have to do is mill, drill and counterbore the slide in preparation for the new configuration. I would just need a centerline height of the internal thread on the nut from it's mounting surface, and dimensions for the screw's lengths and diameters. I'd make the nut out of 660 bronze as I did Darren's elevation nut and the screw from 1117CRS, 1144SP or 1045TGP steel.
You can determine the thread pitch easily by how many thousandths of an inch the dial moves the slide in one rotation, as long as it's direct to the screw and not geared.
As for the mounting, it might be a wise idea to re-engineer the whole thing and get the nut mounted securely with two socket head cap screws from the top side and a cone point set screw between them to adjust/spread the split in the nut to reduce backlash. That's how my lathe is designed and it works perfect (once I get that special lockwasher.)
I'd be willing to make you a new screw and nut, so all you'd have to do is mill, drill and counterbore the slide in preparation for the new configuration. I would just need a centerline height of the internal thread on the nut from it's mounting surface, and dimensions for the screw's lengths and diameters. I'd make the nut out of 660 bronze as I did Darren's elevation nut and the screw from 1117CRS, 1144SP or 1045TGP steel.