I wrote a gerber reader and it was a real learning experience about what different PCB apps do in generating gerbers, wow, lots of weird stuff. The gerber specs were not clear about exactly how some functions worked (they are much better now days) and programmers took a lot of liberties. Same issue for anything that reads gerber, best to keep gerber constructs simple.

I use PADs and I setup my gerber output as  simple. When I generate gerber from PCB design I disable all advanced functions like  apertures macros and polygon fills. So yes my gerber are a little larger but I don't care. For many years now I have never had a "Bad Gerber"  problem. The PCBs may not have been working but I always had the gerber that matched my working image.

If you ever get a bad gerber image try disabling advanced function. An example I have seen is with 360 arcs and poly fills. If you can reduce these to 90 degree arcs and have the CAD tool use simple lines to fill in polys the problems might go away. 

Bob K.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Pete
Sent: Wednesday, December 10, 2014 10:07 AM
To: [log in to unmask]
Subject: Re: [TN] annular rings on internal layers and check plots

I always check gerbers in a third party program.  There's something that worries me about checking gerbers in the same program that wrote them.  The free Viewmate works well if you don't plan to edit.

This does seem like somehow NFPs got removed somewhere in the process.

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