Re: Best cam only software?

--- In CAD_CAM_EDM_DRO@y..., "John Schwab" <johns@m...> wrote:

> Well a primary reason I want NURBS support is that all the CAM

programs i've

> seen so far tesselate to polygonal form before tool path

generation, this

> not only is inaccurate to the parametric surface representation, it

should

> be a needless step. You may think you're getting smooth arcs, but I

bet you

> aren't unless you model is excessively high on the polys. And to

let you

> know IGES is the only format that supports NURBS, but most CAM

ignore that

> or tesselate to polygons on import.

Well here is a little additional information that may help you make
your decision.

1) NURBS is supported by IGES and also by STEP. Also the Rhino
OpenNurbs is another format (3DM) that supports NURBS directly.

2) Most CAM programs internally convert NURBS to tesselated surfaces
when they create toolpaths. I've asked this question of several
vendors and none have yet denied it and have also received whistle
blowers reports privately when the discussions have become public.
This applies even if they have NURBS capabilities. Many CAD programs
do this too.

Delcam has built their reputation on the use of STL and similar
formats for high end CNC CAM applications.

3) Tesselation or approximating a smooth surface with polygons,
triangles in the case of STL files, can be adjusted to meet a
tolerance requirement. If you have a tesselation setting that is
smaller than the accuracy of your CNC machine, no amount of NURB
mathmatically smooth curve vs triangulated surfaces will make a
better surface on the finished part. The part will look, feel and BE
smooth. In fact the velocity algorithms in most hobby controllers
will probably cause more surface variation than the toolpath, except
at very slow speeds.

As far as a CAM program that would be able to handle NURBS, right now
that is limited to a few in the $2000-$4000 range if you want lathe
and mill. Some Candidates would be Onecnc, Visual Mill(not too sure
if they even have lathe), and Excalibur.

For home/hobby use that is a lot of money for CAM software, when
there are alternative software programs that can develop toolpaths as
accurate from STL files for less than $200.

The free ProDesktop does an excellent job of translating IGES files
to STL and has good tesselation accuracy control settings.

Best Regards,

Fred Smith
IMService