Save yourself a lot of problems with the default Eagle files and use the free Sparkfun tutorials. Then use the Sparkfun provided render files for rendering the Gerber and Excelon drill files. Then check ALL the layers with a Gerber viewer and with the DFM pre-check available from a few board vendors.
Also check that the trace widths are set to something more reasonable by hand, for ALL the hand laid traces, and any of the machine laid traces that you forgot to set the sizes on, prior to auto-route. The default traces in Eagle are very thin, thin enough to cause problems with some board vendors, or if you run any substantial current through them. Pay for the solder masks when you have the boards ran, its not worth running without them to save a few bucks. Watch for short jumper traces between main traces and through holes, it has a habit of making those hard to see in the viewer. Zoom In.
Buy the "Adult" version of Eagle and print the boards to check them with actual parts. Especially if you have created your own components. Watch for correct mirroring in the files you send out. Hopefully the folks who bought Eagle three years ago put paid the printing issue in the free version.
While I'm sure some of this has been fixed lately, some versions of Eagle and the included files default out to some weird stuff. I stick to a older version.
The above comes from a expensive lessons learned session a few years ago.
Sound card dacs need to die, but I'd hate to see you hit the thin trace problem with any customers.
Steve
Last edited by mixedgas; 07-15-2013 at 09:58.
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