That is the way it was done back in the 60's. My Dad was one of the first people to make the tool.

Almost everyone who pre-slotted tail surfaces (like Lyle Larson, etc) have used the technique that my Father started using in the early 70's of using a micro saw in a drill press. The 1/64" ply slides right into place. Unfortunately Dremel discontinued the saw (I still have some). But the Chinese stores have some slightly thinner ones that still work.

I've done intense threads on mold making and composite layups, and videos as well. Check them out. You might learn some new stuff.