Re: [CAD_CAM_EDM_DRO] CNC division

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?

Well, I'm still a little vague on how EMC will handle rotary axes.
But, it will handle floating point numbers of fairly high precision.
If you need more than 4 decimal points, it will gladly take them.
So, with the correct constants in the .ini file to make the user units
degrees, you could enter 0.9863 and it would move 360/365 of a
degree (I think that's what you want). If you went to incremental,
entered the A0.9863 (assuming the rotary axis is 'A') and then
went back to absolute, then it would move the right amount from
the current position, and all fractional steps would be dealt with
in such a way as to not allow errors to accumulate. In other words,
each new position is calculated from the home position in floating
point, rather than calculating the number of steps to move from the
current position, thereby forcing all computations to be in intger
step units.

Jon