Re: Machining smooth Curves

Rab,

The "location" of the processing you mention HAS been moving toward
the "end of the line" (pun intended).

There are two issues to deal with in fitting the curve to
the "available points" of a cnc machine:

1) what are the "best" points? Modern computing power has enabled
this aspect to be shifted from a "pre" process to "in" process.
Outside of cnc it is being done with text and graphics daily. BUT...

2) traversing the curve at a constant vector velocity. We don't need
this from graphics or fonts... But it is VERY important to good
cutting of material in cnc apps. And the non cnc uses can employ
"mirroring" and "aliasing" techniques which our cutting process
won't allow.

This combination of correct points and constant vector speed is still
outside of current processing (or software?)performance. From what
I've seen, most programs convert the curve into line segments, and
then use linear intepolation exclusively. In this way, they preserve
the processing power needed to maintain the constant speed. Others
DO "figure the curve" as they go, but these generally do not have the
same smooth cutting. I am speaking here about the "single" processor
type systems this list mostly talks of and deals with. Commercial cnc
controllers may have 5 or more processors working together to achieve
the results expected of both points (1&2 above).

Hope this helps.

Ballendo

P.S. I would love to hear from anyone who is pursuing the "direct"
from bezier or nurbs equations to "available points" of a cnc
machine!

--- In CAD_CAM_EDM_DRO@y..., rab@r... wrote:
> I really don't know that much about this subject, but have seen
> references to NURBS and bezier CAM controls, which sound very
> interesting for smooth, fast machining.
> I use bezier curve toolpaths prior to producing G-Code from them as
a
> large number of small segments, outputting the actual curve would
> appear easier, more accurate and faster than converting to linear
> moves or even a series of arcs.
> It would seem to make sense to interpolate a curve at the time that
> the step/direction signals are being generated rather than at the G-
> code stage, as although the curve would still be composed of small
> linear steps, the resolution would be at the very limit of what
your
> CNC machine could handle.
> Are there any motor driver control programs that work with curves
> instead ( or as well as G-Code ) ?
>
> Rab,