So were laying out a patch, did a pattern using lexan, 1x1 and it was perfect. Marked the skin with a sharpie and had the guy center punch. Used a good drill, and a sharp cobalt bit. Taught him how to remove the usual aluminum from the tip of the bit after each hole and still, out of 25 holes, 8 of them drifted. So after I had a cow, I laid a pattern on a scrap sheet of .050 and drilled it myself. Had minor drifting on 3 holes. When your drilling close to chem mill or the ED is close, this could really be an issue. I usually hit the drill a bit, then once the hole is defined I go on and drill it. Its not practical to use a drill guide for 300 holes.Name:  IMG_9558.jpg
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