Re: [CAD_CAM_EDM_DRO] Re: re:Compucut ?

Rab Gordon wrote:

> Thanks for the replies,
> Could anyone explain the advantages of G-Code over HPGL ?

Whew! Big topic. HPGL is a language for describing pen plots, inherently
a 2D process, without regard to speed. There is a command to set speed
so the pens don't skip. There isn't any tool diameter info in the file, either.

'G-code', a common term for the national standard RS-274D language.
It has provisions to accept at least 9 axes, some linear and some rotary,
and general conventions on how those axes are related. It has provisions
for spindle speed and feed rate control, methods for describing tool diameter
and length, so that programs can be written without knowing the exact
size of tools, and the control can cut the correct shape by compensating for
the size of the tools at run time. There are features for coordinate offsets,
so identical parts mounted in several fixtures can be machined with the
same program. Programs can cut completely arbitrary 3-D shapes,
including pockets with curved bottoms, and curved tops.

>
> My current machine, a Roland uses HPGL to cut in 3D very
> successfully, although I have nothing to compare it with, it contours
> well enough for me. It seems that compucut would work similarly ?

How would you specify cutting a shape like 1/2 of a sphere
(either convex or concave)? If you can do that with your Roland,
the language is NOT pure HPGL, because HPGL does NOT have
a height command, just pen up and pen down.

>
> I don't understand the unipolar v. bipolar thing yet, is there a big
> difference ?

Bipolar drive of stepper motors usually provides a little better
high speed performance.

Jon