Re: cutting complex curves (ref G02, G03)

Joe Vicars wrote:

> From: Joe Vicars <jvicars@...>
>
> In reference to the latest talk about circular interpolation. I
> have a shape that I need to cut that can be described as an internal
> cam. The surface is a mathematically generated continuous function.
> Each point is tangent continuous with each successive point and the
> radii and center positions vary continuously. There are 4 points of
> inflection.
> How do I translate this "spline" into G-code that my shareware
> controller can cut? In theory, I would be generating an infinite
> number
> of circular arcs with the length of each arc infinitely small.
> I have tried some software demos (G-code95) and they simply
> generate
> a G01 with a long list of X, Y coordinates afterwards. This linear
> interpolation has the unhappy effect of producing a faceted surface,
> unsuitable for cams.

What resolution is your physical machine? Do you have a program that
does cut
a smooth path? It is incorrect to say that a list of linear moves will
not reach the
necessary smoothness, if the moves are small enough. For instance, if
your machine
has a basic resolution of .001", then if all the moves are no greater
than .001" on
the long axis, it makes no difference if the interpolation is linear or
circular.
(Yes, these programs may get pretty LONG, doing it this way.)

> Does anyone know of some inexpensive G-code generators that will
> G02/03 from splines? And can you control the "resolution" of the
> individual arc segments. Will an over-sized G-code file crash the
> software controllers?

EMC will take VERY large RS-274 files, many megabytes, at least. If
your control program does not
do lookahead and blending of moves, then it will dwell a moment where
each move ends, and that
will put little 'dimples' at each of these spots.

If I had much of this sort of work, I'd try writing my own program to
take the curve apart and
try to fit small arc sectors to it. It is a bit tricky, because for
each sector, you have to figure
out what the radius of that tiny bit of curve is, so you can correctly
specify the arc.

Jon