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Abandoning the conventional approachMonday, March 9. 2009In which your narrator discovers that the convention way of running
a lead screw drive isn't going to work properly...
I cut the lead screw gear before starting work this morning and knocked the drive together at lunch. It runs fine. 
The problem is that it appears to me that you don't have enough torque to push the drive much beyond 12.5 mm/sec with anything like a useful load.
At that point I did a few calcualtions. My back-of-the-envelope calculations indicated that the kinetic energy in the spinning lead screws at 9 x 10^-3 Joules was more or less the same amount of energy as it took to move a 2 kg positioning table, that is, about 14 x 10^-3 Joules. Now if I turn the thrust nut instead of the lead screw and move either the
nut and the stepper motor assembly or the lead screw, both weighing about half a
pound each, I only require about 1 x 10^-3 Joules instead of 9.
If I have time tomorrow, I will recut the lead screw to seat a thrust nut
and see if I can't get more speed and torque out of the drive.
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Hi, Forrest:
Yes, you are correct. in addition to the power required to turn the relatively large mass of the screw, there is another, even larger problem-- screw whip.
at even moderate speeds, the screw will 'whip' causing vibration that seriously impacts performance and causes lost steps.
you can compute the critical speec of a screw here:
http://www.nookindustries.com/acme/AcmeCharts.cfm
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