Don't forget to account for losses due to leadscrew efficiency.
With ballscrews, expect to lose only 7-10% of motor torque converted to linear thrust. If you use acme screws...I would use 40-50% to be safe.
Your losses from your way system will probably be negligable, so call it zero.
Steppers will lose torque as their speed increases, so ideally you want to operate (CUT and RAPID) at slow SHAFT speeds. This doesn't mean linear movements have to be slow. However, this will require high pitch lead screws that will reduce your resolution. (smallest step linear movement)
You really need to specify a system, not just steppers. What I mean by a system:
-steppers
-leadscrews
-power supply
-stepper drives
-PC/drive computer
For instance, if you go pick out the first set of ballscrews that fit in your machine off ebay, chances are that you will have a compromised system and you'll wish you did things differently. Work out the numbers of the ENTIRE SYSTEM (electrical and mechanical) and you'll see what I mean.
I don't believe that you will have to guess very much to specifiy a stepper system. But you will need to get as much information as possible:
-performance charts for the steppers you are considering
-capabililities of stepper drives you are considering
-what is your minimum required resolution
-how much are you willing to spend? (DON'T forget about the power supply/driver system...this will probably cost far more than your steppers)
-establish some performance requirements and a budget
-consider your spindle performance as well.  |