Gerber help sought

[der Mouse]

>> Everyone seems to want Gerbers, but without documenting exactly what
>> they are.  I found a PDF describing "RS-274X", which appears to be
>> most of it, but there are lots of conventions it doesn't describe.
> That's the spec.  What is missing?

- How do I specfy which layer is which?
- How do I specify soldermask?
- ...holes and vias?
- Is the PDF I have accurate and complete?  (Okay, it probably is not
   complete; it even says it contains just (someone's idea of) the
   commonly-used directives.)

> The Wikipedia page has useful links:
>     http://en.wikipedia.org/wiki/Gerber_File
> You also need an Excellon drill file:
>     http://en.wikipedia.org/wiki/Excellon

I'll have a look.  Thank you.  (Duh...I really should have thought of
Wikipedia myself.)

>> I've found indications that there exists some open-source software,
>> but extracting documentation from code is a mess.
> I dunno about extracting documentation, but gEDA is purportedly
> useful for doing board layout.

It probably would be for me too, if it were to build painlessly.  That
is extremely unlikely.

Also, I like to understand things all the way down - even if I almost
never actually use that understanding, it informs everything I do, and
can border on essential when debugging.

> I use Eagle (from CadSoft).  It's not open source, but it's less
> expensive than most commercial alternatives, and it seems to work
> well.  For nonprofit use, there's a "free" version that's limited to
> 100x80 mm double-sided boards,

Even if I were willing to run code I don't have source to (I'm not; I'd
sooner throw some money to someone on the list to do it for me than run
something I don't have source to), it wouldn't be free even as in beer,
because (AIUI) Eagle is a Windows program, and Windows ain't cheap.

Is there anyone who'd be willing to exchange some files with me -
sample files for me to sanity-check my understanding, in one direction,
and tests to see if my generation is correct, in the other?  I'd just
as soon not have a board made until I'm reasonably sure I've got the
board description right. :)

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