Leadscrew

[fusionkid]

I would use one or perhaps two stages of plain rubber belt speed reduction between the motor and lead-screw (stepper motors, gears and notch belts are noisy)
Bill

So if i was to use an 0.050" lead leadscrew thats 1.27mm per rev so my 2mm feedrate will require 1.575 revs of the leadscrew per minute. (correct me if i'm wrong!)
What would be a sensible gearing ratio? I'm thinking a single stage might be better, to reduce losses/ slip ?? What kind of speed would a servo motor prefer to run at whilst giving me some leeway? This is all new to me, does anyone have links regarding servo motors or tacho generators?
If i was to have 2 or more stages of speed reduction surely i would be better to have the tacho generator driven by the leadscrew itself? Is this ever done?
Many Thanks

[BillTodd]

If i was to have 2 or more stages of speed reduction surely i would be better to have the tacho generator driven by the leadscrew itself? Is this ever done?

It is possible (I have made a speed controller with a feedback from the a 90:1 gearbox) but, because of backlash in the gearbox, or flex in the belts in your case, motor speed can be hard to stabilise (this didn't really matter in the above example).

It is far better to control the motor speed with a close coupled tacho. There are many different type of tacho feedback; some have DC generator coupled to the motor shaft, most PC fans have a magnetic sensor that's part of the brush-less motor driver but, most modern servo motors will have an optical encoder wheel.

There are plenty of tacho feedback motor speed controller chips and designs around.

Old cassette machine motors used to use a centrifugal switch that modulated the windings directly, which looked crude, but worked incredibly well.

You might be able to get away with a simple back emf speed (sometimes referred to negative resistance generator) since your motor load will not vary very much. All you need is a stability (low wow and flutter) , the actual speed is not critical

to be continued...

[fusionkid]

So i've been looking at leadscrews and found a sales pdf with some useful notes about leadscrew design considerations
http://www.automotioncomponents.co.u...ngular-nut.pdf

But i seek more information........