CNC 101 was Re: what is POSTPROCESSOR? a fundamental question

Marcus,

Darn! I was feeling pretty good about that explanation...
Perhaps a bad example on my part.
Keep in mind the intended recipient of the post...

I was attempting to show that machine limitations (in my example, the
mower with large turning radius) will ALSO be considered by a modern
post processor. And that in doing so, it WILL modify the ACTUAL
toolpath so that the limitations of the machine are not encountered.
(trying here to give an analogy for the "cut with the periphery of
the cutter instead of the tip", as mentioned by Doug)

I can see that my use of rows vs. circles might have been confusing;
as a post processor would NOT typically make that sort of change.
BUT...
IF the cnc control WAS driving the mower of my example, then it WOULD
have to use something like this "change from rows to circles"
strategy!

The main thing is to understand that a MODERN post processor does not
ONLY translate the toolpath into a new dialect; but MAY also CHANGE
the toolpath to address limitations of the machinery used. It is this
aspect of "posts" which seem to be confusing Jerry. (and likely
others, as well.) Since most people only think of the "direct"
translation part of the post as being the WHOLE post processing.
(Which WAS the truth for decades; at least on the lower end of the
price scale.)

One thing we have to endlessly keep in mind is that this cnc thing is
evolving... What a post did only a few years ago, is not the same as
what a post is expected to do today...

AND, with mfrs. scrambling for markets and market share, the lines
which used to be fairly clearly drawn(between CAD, and CAM, and CAE,
and CNC) have become VERY blurred. As Fred S said in his reply using
Vector as an example:(paraphrased, with my emphasis added) Where the
post WAS just a translator added to the end of the process of CAM, it
is NOW fully integrated into the entire CAM program/process.

Hope this clears up the confusion,

Ballendo

P.S. One of the difficulties of answering questions on a list like
this is knowing that the person I am responding to might never have
seen a higher end (or lower end) program. Certainly masterCAM and
featuremill use the integrated approach you describe (and which Fred
also mentioned), BUT lots of other simpler and/or older programs WILL
simply be g code translators, with no "knowledge" of the machine
kinematics... But the cnc world is changing daily! It is this
endlessly moving "target" which makes lists like CCED useful, but it
also leads to some: "but I thought you said it was..." (when there
may be two or more answers, but we are only talking about the one
which will help the individual we are addressing in our response.
Laying it all out initially could just confuse things more.

P.P.S. If I were SURE Jerry WAS a computer programmer, this would be
MUCH easier to explain, as that discipline uses things which are a
direct analogy for what we do with CAD CAM CNC.

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Marcus & Eva" <implmex@a...>
wrote:

> Hi Ballendo:
> I am puzzled by the comment you made (snipped below).
>
> > The post processor is what "decided" to use the wide overlapping
> > circles instead of the back and forth rows to cut the lawn. It

had to

> > consider the needs of BOTH the part geometry AND the machine
> > capabilities to create the necessary mowpath (toolpath).
> >
>
> My understanding was that the post processor merely translates the

toolpath

> information from the CAM output into G code, and that the operator

creates

> the inputs via dialogue boxes to set the cutting strategy.
> I further assumed, that the internal calculator within the CAM

program

> (ahead of the post processor) was what determined the actual places

that the

> tool was intended to go, and in what order.
> That certainly appears to be how Mastercam and Featuremill and Work

NC

> operate (these are the CAM programs with which I have the most

experience)

> Mastercam, for example, creates an intermediate file called

an "NCI" file

> containing all the position and tool parameter information that is

then

> translated to G code by whatever post I choose.
> I still have to choose to make parallel vs circular cuts, and I do

so by

> accessing dialogue boxes on the GUI in the CAM program (not in the

post)

> and selecting my preferences.
> Are there programs out there that do this differently?
> I always assumed that they were all essentially alike.
> Cheers
>
> Marcus