This one has a bit more specs about accuracy... if I could trust them :I
http://bjwn.en.alibaba.com/product/215200677-200438444/Motorized_Rotation_Stage.html
On this rotary stage sizes is usually nema 17 frame size, so with 1:180 ratio I
could expect minimum 40Nm of torque?Isn't usually there a "mechanism" that
allows to tighten worm against worm wheel to reduce backlash?
>
> That device has a resolution and a repeatability specifications but no
> accuracy
> which worries me.
>
> A few years ago I measured some rotary tables and found most of them
> were useless for the job we were doing due to periodic error due to
> the worm to wormwheel engagement, a basic sawtooth error which in one
> case was nearly .75 of a degree.
>
> Currently on my 5 axis I use a Vertex brand rotary (Taiwan) which has
> a 90-1 worm.
> So far for clock gears it has been good enough but I have not measured
> the accuracy beyond checking the resulting manufactured gear pitches.
>
> To provoke the error from a worm cut a gear of much higher number
> number than the internal worm. Simple check is, get a digital vernier,
> pick a number of teeth to measure over, measure , zero the vernier,
> then step around the gear, any time the vernier reads negative zero
> it, repeat till you get a lap just positive and record the peak
> distance, should be very small for a good rotary. I have seen some
> terrible variation from some rotaries.
>
> Backlash in these low cost rotaries I avoid by writing directional gcode.
>
> Dave Caroline
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