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So far we've seen that all of the Gerber files have imported correctly and that the artwork looks like what we saw on our original CAD layout screen. But what about the drill information? If your viewer program supports drill previews you can examine the NC drill data in the same manner as the Gerber data. Lavenir's ViewMate program supports drill previews as does Graphicode's GCPrevue program. Now let's look at the drill layer data.

Notice that the drill information (the three blue circles) imported with the correct sizes but mirrored along one axis. Again, this is common and does not present a problem. Also, the drill information may be significantly offset from the Gerber information. Prior to board fabrication, the drill layer is lined-up with the thru-hole pads.

At this step, the problem most commonly observed during previewing are drill sizes that don't make sense. If you see very large or very small holes, or holes that are crowded together or spread apart,  it most likely means that same leading/trailing zero suppression or m.n format problems exist as in the Gerber examples. Check your CAD program settings and regenerate the NC drill files.

If you've gotten this far and everything makes sense, you're ready to submit your files for fabrication! 

You can check the validity of your imported data by viewing the list of D codes (Gerber files) and T codes (NC drill file). Examples of these two lists are shown below for the board files used in this tutorial.

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