Contouring and CVV was Re: DeskNC for Windows experience anyone?

Chris,

I don't know if the MillmasterPro/windows has contouring or not. As I
said, I have not used it. But the advertising I did see, mentioned
improvement of several items which I am aware were problems with
their DOS product.

Flashcut has had contouring, but by whose definition? And other PC-
based cnc controls also beg this question.

There are generally two definitions of contouring used with cnc; one
older, one newer.
In the olden days contouring simply meant the ability to move in
OTHER than orthagonal/diagonal directions(straight lines), which
means curves could be cut. At first this definition was for xy moves
only, then it was updated to include 3 axis moves (so then contouring
meant curves possible in one of 3 planes at a time, but available in
all 3 planes, xy xz,yz).
The newer meaning of contouring would be more properly called
constant vector velocity(CVV). This is similar to the ability
to "drive" on a flat twisty road as fast as possible, slowing only
enough, and only when necessary. True 3d contouring would mean that
the "road" is a twisty mountain highway, and cnc is the racecar
driver. So you can see that the word "constant" is not entirely
accurate; the idea is that the control is attempting to maintain
constant vector velocity (feedrate) throughout the toolpath.

Some of the current controls claiming "contouring" do not really do
CVV, and the history of the terminology lets them off the hook. Is
being able to negotiate a fairly straight road, with occasional
curves, the same as that twisty mountain road? No.

The earliest solution was to begin the next moves' accel at the same
point that the current moves' decel began. This is still the most
common form of "contouring" in commercial cnc machines. The down side
is, the "corners" are rounded when using this approach. (corners may
also be rounded by servo following errors) Inaccuracies from both
following error and the accel/decel contouring algorithm increase
with higher feedrates and also with increased toolpath angle change
between blocks.

True contouring(CVV) requires trajectory planning, the same as when
WE use our eyes and experience to drive those mountain roads. It is a
recursive process, made more so by the fact with cnc that the speed
may be changed at any moment (by the operator) AND the limits of
memory for "lookahead" (just like our trying to see around the next
curve to know how fast we can "take" this one...)

So the next form of CVV was created: pre-processed files. This means
the entire toolpath is analyzed and internal commands "added" to
adjust the speed/feedrate. This IS true contouring, BUT usually does
NOT allow changing feedrate during the toolpath execution.

We have now come to the place/time in our computer capabilities that
this can be done "real-time", allowing feedrates to be changed on-the-
fly, while still maintaining the most CVV possible, given the limits
of the physics acting on the machine. Expensive controls (and
Master5) do "real" trajectory planning. I'm not sure where EMC is at
this point in time.

Why bother? Faster toolpath execution. Better tool life. Better part
finish.

Again I will say that many of the "supposed" contouring claims are
not valid, except by the old definition(s). Try feeding a "twisty
mountain road" toolpath with hairpin curves and long/short
straightaways and the truth will be seen...

A spiral getting tighter and tighter will also prove instructive, as
will toolpaths made of arcs compared to toolpaths of "arcs" MADE of
short line segments (as an approximation of the arc; often the output
of a CAM program). These short segments should process at the rate
that the "overall curve" they are defining would be processed as an
arc command.

Hope this helps.

Ballendo

--- In CAD_CAM_EDM_DRO@y..., Chris L <datac@l...> wrote:
> I've noticed that MicroK does not mention "Contouring" anywhere. At
least I
> did not see it. Looks like a replacement for the program they had,
just
> windows.
>
> One other issue, Flashcut already has contouring, has had it for a
few years.
> Maybe you are thinking of Feedrate Override while Contouring?
>
> Their upcoming version will have the increased step rate output,
offset comp,
> and long file naming (32bit). I have heard that it is not all that
far out.
>
> Chris L
>
> ballendo wrote:
> (snip)
> Also, Microkinetics has released a windows version of their
>
> > millmaster software. I've not used it, but the advertising for the
> > windows version seems to address the "known" limitations of the
> > earlier DOS-based product it is based on; suggesting that the
> > corrections to a very mature platform (the dos-based product was
sold
> > for about 12 years) it might make a good choice...
> >
> > And Flashcut is a very user-friendly Windows interface. Their
newest
> > version also claims contouring (constant vector velocity)
capability.