[NIC 77]

A larger lead does require more motor torque to produce the same thrust. Double the lead, double the torque requirement.

Yes and No. If you're talking about something that is providing a force while not moving, that's true.

When a machine is accelerating into a cut, it's different. The available torque from the motor to provide "thrust" or what I would call "available cutting force" is only what is left over after accelerating the axis.

For stepper driven systems you'll hit a speed where a higher lead ballscrew can actually provide more cutting force. This is in part because the torque of a stepper falls off with increased RPM. You might be limited to 200 IPM or less with a 5mm lead ballscrew, but be able to attain 350 IPM with a 10mm lead, and have more cutting force than the 5mm from let's say 150IPM and onwards in the speed range. Whereas the cutting force available with the 5mm lead will be a ridiculous amount, that you would never use, at lower speeds. It's just a generalization, because the diameter of the screw and the acceleration settings play a huge part in it.

Servos, it's a different story obviously as the rated torque will be continuous for most, if not all, of the RPM range. Really, I'd have to put the numbers in my spreadsheets to make a comparison between different leads and diameters for a given acceleration and motor. 32mm diameter ballscrews have substantially more rotational inertia than 25mm diameter ones.

My questions for the OP would be what kind of acceleration and top speed are you going for? And what are the lengths of your ballscrews? What 750W servos would you use, link to a datasheet? Do you want to turn this thing into a speed beast with 0.5G or more acceleration? Is using a belt driven gear reduction out of the question? For example, 10mm lead with 3:1 gear reduction from the servo.

The fact that it's a mill conversion with Ways instead of linear rails (is that true?), also makes it harder because the friction of these components...I don't know how to deal with them.

3) how long would a set of 32mm c7 rolled ball screws on x and y axis last if the machine was not used day in and day out

The higher end manufacturers will supply all kinds of calculations to figure that out. The lower end ones don't. 32mm diameter ballscrews are overkill. 25mm diameter with 750W servos is fairly common I think.

Actually, 20-25mm diameter, 750W servos, and 5mm lead are fairly common things for a mill conversion. If you were going with steppers I would say to definitely use a 10mm lead. If you are going to use 32mm diameter I would say to use a 10mm lead also. Just my opinion.

Have a read through this thread:

https://www.cnczone.com/forums/verti...rum-posts.html

And the one below from post #71 onwards (10mm vs 5mm lead and 32mm dia vs 25mm dia, same thing as you, actually look at the graphs in post #73 I made for someone else, there's my opinion, it will be about the same for you):

https://www.cnczone.com/forums/servo...-servos-4.html

4) are c7 rolled ball screws able to produce quality accurate end products.

It's not the C7 rating per se that is your biggest concern. It would be the backlash in the ballscrews. Many different manufacturers of C7 ballscrews. Some have backlash, some don't. Buying stuff from China can be a bit like rolling the dice. I'm not an expert on it really.

I don't think I'd pair a 16mm diameter ballscrew with a 750W servo, I'd be too concerned about damaging it, but like Jim said, you could tone down the servo output. I don't know anything about driving quills, I'll say that right now.