Quote Originally Posted by Bob_series1 View Post
I will be supporting the lead screw but just wanted to put in a worst case. However, from your spread sheet it makes a massive difference to the power requirements. :surprised:
With big leadscrews the key thing is screw inertia and acceleration... a big screw operating at high cutting speeds needs high acceleration (short acceleration time) to be able to follow a cutting line.. and that needs torque AT THE REVS IN QUESTION... this is the thing that most people miss... its not bottom end torque you need, its torque at the top end... and as you say, you need to drive them optimally to get that.

The method of supporting the leadscrew does not directly affect the motor requirement, it affects the critical speed above which the screw starts to whip, putting sideways force on the nut and adding friction (as well as a nasty vibration and a poor cutting finish). But adding a better support configuration means you could go for smaller screws, and since inertia varies as the fourth power of the diameter even a small reduction in screw size can have a dramatic variation in motor requirement... or for the same motor get better performance... I cannot find a spec for a Tr20x6 screw, only 16x4 or 20x4 - given those two I'd go for the 16x4. You might also look for a 16x4, 2 start. (same as a 16x4 but the lead is 8mm so you get twice the speed, or more importantly, you need half the motor revs for the same speed). Anyway, its worth playing with different screw sizes and types (1/2-10 2 and 5 start ACME is popular in the US).

Note also if you are going for dual screws you need to consider how you will drive them... if you use one motor and a timing belt/pulley arrangement you need to add the inertia of two screws together plus that of the pulley arrangement to get the required power... in this case it will be more than twice the single screw arrangement.