I am looking for information on the most popular [G/M] cnc file
layouts.

As some of you may remember I am writing a program to convert
HPGL files to cnc files. The reason for using HPGL rather than
dxf for input is that the HPGL files have the actual vectors for
text, including ttf, where the dxf files contain the text
strings.

I discovered a free GNU program called hp2xx that will take
regular HPGL and HPGL/2 files for input and generate an output
file using only PU [pen up], PD [pen down], and PA [plot
absolute] commands, with some other extraneous [for my purposes]
commands such as IN [initialize plotter]. This eliminates the
more problematic conversions such as converting AR [arc relative]
because of the difference in the way cnc controllers handle the
arc commands. The downside of this is that a single line for an
AR [arc relative] command is replaced with a huge number of short
absolute G1 moves.

My program called hpgl2cnc is nearing completion. Rather than
attempting to write a complete cnc program, this generates only
the G0/G1 codes that will need to be cut-n-pasted into a complete
program with headers to start the machine and footers to properly
shut it down. The program has the option of either metric or
inch code generation and will run in the "console" [dos box] of
windows xp and 2k. [I had to buy a new compiler (PowerBasic
CC4.01) to do this.]

HPGL plotter units are 1016 to the inch or 40 per m/m. Accuracy
will be 0.001 inch or 0.05 m/m. You will be able to set a
different plunge [z] and lateral [xy] feed rates. You will also
set a "clearance" above the part and a "plunge" distance into the
part in either inch or metric.

Specifically I need to know what is the most common/portable cnc
output file format suitable for cut-n-paste:

Line numbers? - how many places? Sequential or every 5 etc.

Include decimal points? If no decimal points what is assumed
accuracy?

Leading or trailing signs? -0.123 or 0.123- also do you want/need
+ signs?

Spaces between variable name and value, i.e. "X0.123" v "X 0.123"

Comment indicator? "%". " ' ", "*" or what?

== Is column alignment still important? If so what spacing? ==

== I am including range checking on the xy and z feed rates.
What is the min/max in inch and/or metric that you think you
would use? I am using IMP in the inch mode. What is the accepted
metric feed rate unit?

While HPGL2CNC is generally intended for plaques, I can see doing
2 dimensional contouring such as flat cams. With the ability in
most cad programs to turn layers on/off, some elaborate work
should be possible, with the manual insertion of G41/G42 codes
and T specifications.

Thanks for your advice.

I will post the compiled exe program and PowerBasic source on my
website and submit for inclusion on some of the other cnc sites
and the PowerBasic site. This will be freeware under the GPL.
If you would like a copy when it is completed please send me an
email. Most likely not the program to use for high volume
production, but may be just what you need for a one off plaque or
sign.

I'll start work on the 'C' axis version for engraving around a
cylinder when this one is up and running.

Uncle George