Justin - my largest set is an 18, meaning 18 lines per inch. But I do a LOT of skip-line checkering, and thus I have a spacer for that.
You can do your two crossing lines with a single cutter, then start spacing them with the 9 cutter. The smooth blade will ride in the first line while the cutting blade makes the new line 1/9th of an inch further on.
Use the single cutter to deepen your lines. And don't worry about the 2.5:1 angles, etc. All the early checkering I've seen has been square, with the lines crossing at 90 deg.
I made a ML pistol for my son last year - barrel was 16.357" long, so it had a forestock on it that was checkered so as to give him a grip. Butt of the pistol was checkered using a #10 spacer, then a little sterling nail put in the center of the squares. About used up all my patience, but it looks great.