Re: How to go from 2.5 D to real 3 D ??

All,

Northwood Designs whose site I've just found, discuss this in their
technical White Paper at:
http://www.nwdesigns.com/Tech_paper.htm

To quote:
"Arcs may be fit in one of three methods: 1) relative to the standard
orthogonal planes (XY,XZ,YZ). 2) relative to any rotation of the
standard orthogonal plane. 3) to completely arbitrary planes (3D
arcs). Almost all controls will machine arcs using the first method,
some controls will allow method number 2, and a few controls are able
to machined true 3D arcs. (*note- a 3D arc is not a helix)."

They actually have a program that converts a file comprising of many
short linear moves into arc movements or NURBS curves for controllers
that have difficulty with high resolution files.

Their site has a couple of demos and info on the subject, well worth
a visit.

Hope this helps,
Rab

> We do plenty of arcs in XY plane (G17), and perhaps some do arcs in

XZ

> or YZ (G18, G19) as well. As far as I've learned, arcs must be in

one

> of these planes, unless line segments are used to generate an arc.
>
> Are there controllers (and CAD programs) that can generate true

arcs in

> other then these defined planes? I can see how to draw an arc in

CAD,

> and then rotate it in an axis. I don't recall any Gcodes (NIST,

RS274)

> that hint at a way to revolve, or define a plane in either then the
> mutually perpendicular planes. I have no idea "how they do it".
>
> So far, my CNC needs/interests have been met by "edged" surfaces. I
> anxious to experiment with "water line" cutting, and smooth

contours.

>
> Alan KM6VV