Hi Mike, I just use some real thin basswood sheet and cut squares of the desired size, then I use a ruler and a .5mm pencil to draw the lines "with the grain". You can run a scribe across with similar results. Then I glued some cut match sticks under and applied some indian ink/alcohol wash. You can poke nail holes in it before wash too and they will pick up the ink, along with scribed lines.
The coating on the gears is 50/50 flat cammo green/gloss black, then just a little white to get an almost black shade of semigloss green slime. They come from a junk motor gearhead. Next time junior takes apart something expensive, just pat him on the back, pick up the gears, and make an eaod!
I've shrunken them down. The original ones are on the left in the top piccy, the rest are 5 and 8 ft in N scale. I'll keep the larger ones in HO land...