Re: [CAD_CAM_EDM_DRO] CNC division

Hi Ian,

If I can use the Sherline rotary table for an example (72:1 worm gear),
with a 200 step, 1/2 step drive, You'd have 28800 steps per 360
degrees, or resolution down to 1/80 of a degree. Each "edge" of a gear
tooth would be accurate to +- 1/2 of that, or .00625 degree! So that's
a LOT better then 1/2 a tooth! You'd want each gear edge to be a
percentage of the full rotation, so that there wouldn't be any
accumulated error. That's done at the CAD end, if you're using cad, or
you should calculate each edge as N/(2*365), where N would be 0 -> 730
(takes twice as many edges as teeth!), I'm sure you get my drift!

Hope I was helpful.

Best regards,

Alan KM6VV

Ian Wright wrote:

>
> Hi,
>
> I've been thinking about running a dividing head / rotary table under cnc
> control and was wondering how the division is usually arranged. As most
> divisions will not be whole numbers of steps on a stepper or encoder, you
> obviously can't just tell the thing to round up or down the error as you
> will likely finish up with a 364 1/2 tooth wheel instead of a 365 one (for a
> year calendar on a clock). So, with a slight bias towards EMC, can you have
> the cnc software do the necessary computation to get closest divisions or
> would you have to do it with a hand-calculated canned cycle for each number
> of divisions - or perhaps some other way?
>
> Ian
> --
> Ian W. Wright
> Sheffield UK
> www.iw63.freeserve.co.uk