Re: MaxNC modifications

Ron,
I may be wrong, but I'll stick my neck out here.
Software which drives steppers, usually has a much higher precision that the
positioning precision.
They normally keep fractional steps in a error register until the error
amounts to a full step - which is then moved out to the stepper.

Mo

> here's another slant on the situation...
>
> since you report some part patterns can be machined with no errors, yet
> other patterns show the error, let's consider a method that could produce
> the errors even if the steppers never lose a a step.
>
> taking a hypothetical machine that has steps at .001 inch, let's move
> X 1.000 inch, but move back with three equal moves. no matter how far
> we carry out the precision of the calculation, each of the three moves
> will be .3333333333.... inches. our math will have any degree of
> precision we want, but the machine will be forced to round off our
> calculation. we move plus 1000 steps and move minus 333, 333, and finally
> 333 steps. we see an error of .001 but our stepper didn't lose a step.
> now move 2.000 inches and back in thirds. we move plus 2000 steps and
> then move minus 667, 667, and 667 steps. now our error is -.001 inches.
>
> this is just a condition of G91 programming. it happens with servo

machines

> and stepper machines (although some servo machines can keep internal
> register precision higher than the positioning precision)
>
> -ron