Re: Thoughts on Gcode interpreters and CNC controls....

Carlos,

I know what you mean about IndexerLPT. That buffering ahead of
execution is something I can't find in any of the other low end
stuff. For me, Indexer's lack of feedrate override is a big minus.
Although the developer tells me it'll be ready "anytime now".
"Anytime now" is relative. He's been telling me that for a few years.

Regarding continuous contouring, the Ahha system I helped the wood
router guy with had that mode. We could never get it to work, he
always had micro dwell, burn marks on his wood between blocks. The
only way to eliminate them was to turn off cutter comp and program to
the bit's centerline.

Thanks,

Doug


--- In CAD_CAM_EDM_DRO@egroups.com, "Carlos Guillermo" <carlos@v...>
wrote:

> Doug -
>
> I wonder the same thing. Matt's input on lookahead is what we're

talking

> about. It seems that most controls like to quote a number in terms

of

> blocks, but I don't see how that can be a fixed number. I would

think it'd

> depend on the actual g-code. Like he said, EMC starts looking

ahead as soon

> as it starts running a program, and can usually get very far ahead,

at least

> for most programs. Some motion controllers, like IndexerLPT (wish

there was

> a Windows frontend...) do process the entire program before

beginning the

> cut. I also hear about other controllers that have a "continuous
> contouring" mode (ala Flashcut?), which I believe is a way to allow

the

> pre-processing, but I think you run into problems this way with

feedrate

> override, and stopping/holding/starting/backing up/etc. during the

motion.

> It's got to be tricky to be able to pre-process everything and vary

the

> feedrate during the motion, unless you work off of a variable

frequency

> hardware clock or have a few tricks up your sleeve.
>
> Carlos
>
>
> > Group,
> >
> > Since there's a fair amount of CNC knowledge in the group I'd

like to

> > throw out a topic for discussion.
> >
> > A typical CNC controller operates on Gcode programs in what would

be

> > called an interpretive mode. As opposed to having an already
> > compiled CNC program to work from. In other words it scans

through

> > the program as it's executing it and forms the motion commands in
> > real time. Sometimes it's obvious that this method slows down
> > program execution, especially when you're trying to do continuous
> > contouring using cutter comp on slower controls. An example

would be

> > Ahha, I saw a wood router guy trying to contour with cutter comp

and

> > it was a disaster because of the micro dwells between code blocks.
> >
> > My question is, why don't controls have an option to pre-scan a
> > program and by accessing the tool and part offset tables pre-

calulate

> > all the cutter paths so that when actually cutting all the

controller

> > has to do is deal with interrupts and motion control? Or do some
> > controls have that ability? I've asked this question to a number

of

> > sales engineers at trade shows, but was never sure any of them
> > understood what I was asking. The nearest I came to getting an
> > answer was from a Mazak engineer who thought Mazatrol had

something

> > like that.
> >
> > Any thoughts?
> >
> > Thanks,
> >
> > Doug