Re: [CAD_CAM_EDM_DRO] How do you get 6/10 of a step?

"John D. Guenther" wrote:

> Ok, here is my dumb question for those that know how all this stuff
> works.
>
> If you have a stepper motor running is 1/2 step mode so that there are
>
> 400 steps per revolution attached to a 20 tpi lead screw you get 8000
> steps per inch. Now supposing I want to move that axis exactly 1.0197
>
> inches, that would appear to me to take 8157.6 steps. The question is
>
> how do you get the 6/10 of a step? I know, that is only .000075 of an
>
> inch, maybe I am being paranoid about precision but it seems to me
> that all this can accumulate to quite a bit over many moves along the
> same axis.

No, you must do your calculations so it does NOT accumulate.

> Is it the common practice to round up or down when
> calculating the number of steps to move?

Yes, you do the rounding on the number of steps to move, but NEVER round

the actual position. So, you don't assume your requested position is
the
actual position when starting off after an imprecise move. You always
keep a count of actual position in some integral form, either steps,
inches x 8000, or some similar artificial unit, to remove this
possibility
of accumulation of rounding off error.

Jon