Thread: Some Advice
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16-05-2020 #1
They will be very expensive with the only advantage being no rotating screw. The disadvantages of cost and lower resolution/efficiency would far outweigh the one advantage.
However, with only 1500mm travel required there is no reason why you can't use a standard ball screw without any issues provided you are not wanting ridiculous feed rates.
The trick is keeping the screw speed down and this can be done by choosing a higher pitch and then gearing it down with a ratio. The gearing brings it back to the desired pitch to give speeds required but it halfs the Screw speed which stops any whip. ie:
Let's say you want 10mtr/min cutting speeds and you are using typical stepper system that provides usable torque up to 1000rpm.
Normally you'd select a 20mm Diameter with a 10mm pitch that will spin the screw at 1000Rpm to give 10mtr/min, however at 1800mm then you are likely to get whipping.
But if you use 20mm pitch and 2:1 ratio then screw speed drops to 500Rpm and you still get 10/mtr/min speeds and keep the same resolution because the ratio effectively halfs the pitch back to same as 10mm.
The ratio also effectively doubles the torque but this is offset because of the 20mm pitch as a lower linear torque than 10mm but still, you can see the advantage this method gives.
I've built several 8x4 machines using this method and they work fine. My preference is a rotating ball nut but it's much more costly and complex but for a 4 x 4 machine I wouldn't hesitate to use this method.-use common sense, if you lack it, there is no software to help that.
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