Re: CAM generating short lines not G02/G03 curve segments

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Doug Fortune <pentam@c...>
wrote:

>
> I'm trying to graduate from hand gcoding, some of my projects are

pretty

> complex (such as the master rod for a 7 cyl 125HP homebuilt radial

engine

> I'm working on.. see http://www.hciaviation.com/prod-r220-

a.shtml )

>
> See the master rod shape near the bottom of http://www.cnckits.com/
>
> I've generated the DXF file (which has a whole bunch of stress-

reducing

> curvey but strictly portions-of-circles cuts), but I'm having

trouble

> locating a CAM package which translates the DXF file into portions-

of-

> circles cuts (ie G02/G03).
>

Doug, your are probably defining your shapes as a spline of some kind
and the DXF interpretation is a series of linear approximations.
Vector Cad has a function called Arc-Spline. It fits arcs to a chain
of lines ( a cubic spline or a poly line) and replaces the lines with
arcs that fit within a tolerance that you specify. Creating the G-
code from this will make arcs. If you use a drawing program like
Corel Draw or similar, it may not be capable of exporting the shapes
as arcs. Most Cad-cam programs have this capability.

Alan's method of re-tracing, uses 3 points on the curves to make
arcs. It will allow you to more carefully control the sizing and
placement, but the actual final accuracy will not change much. For
free flowing shapes this can be a time consuming process, whereas the
arc-spline routine is an eyeblink of time. Also there should not be a
need to use arcs to cut your shape. Most of the current controllers
will cut a series of straight lines using some kind of constant
velocity planning and the series of lines will cut just as smoothly
as the original designed arcs.


Fred Smith - IMService