Re: [CAD_CAM_EDM_DRO] What is G-Code really? (Was Gerber to final PCB)

ghidera2000 wrote:

>I just finished a chat with a Gerber format expert and he's telling
>me that its not possible for G-Code to be 274-D because 274-D has no
>aperature information in it.
>

Right. The original Gerber code may have aperture info in it in the form
of COMMENTS, but most programs don't read it. They expect the aperture
definition to be in ANOTHER file.

Just to be absolutely pedantic, I quote the first sentence from the
"Gerber Format Guide", published by Gerber Systems Corp in 1994.

"Gerber Format defines a family of data formats, the most frequently
used of which are subsets of EIA Standard RS-274D."

> Only 274-X has enough information to
>actually mill a workpiece without a human operator to set the
>aperatures manually.
>
>Or is G-Code based on and extended from 274-D?
>
>

Mill a workpiece? Apertures? How do you MILL with an aperture?
The apertures are images to flash or draw on photographic film.
And, as they can be square, oval, hexagonal, or whatever, they don't
resemble drills, mills, or any other tool, except possibly a punch.

Note there is NO SUCH THING as "G code". That is a slang reference
to RS-274D, an EIA standard for machine tool control. "G-code" is
not BASED on RS-274D, it IS RS-274D. But, the definition of RS-274D
leaves a LOT of room for interpretation, which different CNC control
vendors did with abandon, to the extent that there are now "flavors"
of g-code. The very original Gerber photoplotters had a fixed aperture
wheel, and it cost thousands of $ to have one made up. So, the PC board
fabricator had his wheel made up, and he told the PCB designer what
apertures would be available, and if he needed it changed, he got hit
with a several thousand $ setup fee for that service. Now, of course, it
is all done with computers and turned into pixels, so the apertures can
be changed with abandon.

RS-274D has tools (Which Gerber uses to select apertures with the D
word). There is the T word and the D word. T selects the next tool to
use, and it can be selected in advance. The D word brings that selected
tool into the spindle on machines with auto tool changers. Every CNC
control vendor has different ways of setting this up. There are also
radius and length offsets that are kept for each tool.

Jon