RE: Why can't I re-run this program?

Hi Jon,

Thanks for the comments. I don't think I've seen any REAL contouring!
I thought 1000 line (block) part programs were big! That look ahead
must be tough to figure out. Sounds like you either get subroutines, or
look ahead!

Alan KM6VV

Jon Elson wrote:

>
> Alan Marconett KM6VV wrote:
>
> > Hi Jon, Ray, Tim et. al.,
> >
> > That's what I figured (after I searched a considerable time trying to
> > find subroutines). Is it because the Gcode is pre-compiled, or because
> > of the "contouring" (?) process that smoothes the flow of the blocks?
>
> It is not "pre compiled". The interpreter DOES look ahead, and they didn't
> do the extra work to have the interpreter follow through a subroutine
> to keep track of any reasons it might need to slow down there. That is
> the whole reason for the problem, that it has to look ahead at least as
> far as it would take to slow down. For instance, if there was a long
> string of very small, almost parallel moves, and then a sudden right turn
> or reversal of an axis. This is a common situation in contouring. The
> machine might have to slow down hundreds or even thousands of blocks
> of G-code before the actual discontinuity in the motion, or it would
> exceed the machine's acceleration limits, and gouge the work.
>
> > I'm also curious about the G98/G99 "canned cycle return level", is that
> > widely used? I understand that canned cycles can vary a lot.
>
> Canned cycles are very irregular, and are generally specified by the machine
> tool BUILDER. The CNC maker then programs these required functions
> into the CNC control as requested. that's why you can have the bizarre
> situation of two apparently identical machines side by side in a plant
> (bought at different times) with different canned cycles!
>
> Jon