Re: [CAD_CAM_EDM_DRO] Again, What is True 3D?

joe wrote:

> When you guys talk about "true 3D" what are we really talking
> about? To my knowledge, G-Code only supports motion in one plane at a
>
> time (not counting helical interp.) , so no matter what you do it's
> only
> the summation of 2D moves.

No, I'm afraid you are wrong. Some older CNC controls supported motion
in
only two axes at a time, but most of those were replaced in the late
70's.
Nearly everything I know of supports motion in 3 (or more) axes at a
time.
Now, standard G-code (RS-274D) is limited to arc moves in one of the
3 orthogonal planes, but vector moves are not constrained at all. You
can
specify a block like
N123 G01 X1.234 Y2.345 Z3.456
and it will make a linearly interolated move in 3 axes simultaneously.

> I feel like the real distinction is in the code posting software.
> If you go to buy Gibbs or MasterCAM you will pay about 7 to 10 grand
> more for what they call "Full 3D" or "Solids". I have yet to have
> anyone explain the difference to me. Am I missing some basic
> understanding of G-Code? The output of any post processor has to
> consist of arc segments and lines (In Plane). There are no 3D curves.

It is not in the G-code, it is in what the CAD -> CAM translation will
do
to convert a mathematical description of a solid surface into the G-code

needed to cut the surface.

Many of the higher-end solids packages will allow you to graphically
define
a basic 3-D structure by combining elements of cylinder, ellipse,
rectangular
solid, etc. and then blending the surfaces with draft angles, ribs,
fillets and
such. You can also subtract material by having the same graphical
elements
chopped out of the structure. Think of things like plastic housings for

small tools, engine blocks, and the like. Now, tell the software you
want
to cut a MOLD for the part, not the part itself. Tell the software that
the
material is ABS plastic, and that there will be a shrinkage of 10%, and
it figures out how to reshape the mold such that the part comes out
the shape you defined. This is what the high end packages do for you.
Automatically cutting out the mold cavity for one of these complex
shapes is a difficult task, and requires extensive study and thorough
testing, or there will be dimensional errors, gouges, crashes, etc.

And, a number of high end CNC controls DO have a variety of 3-D
curve features, from arbitrary mathematical equations defining the
surface to be cut to NURBS (Non Uniform Rational B-Splines),
another way to define complex 3-D curved surfaces. These features
are non-standard, each control has its own way of doing it, so
it keeps the post processor writers busy.

Jon