I recently picked up a scrollsaw. The blades that it uses are pretty amazing, they almost wire thin but sharp enough to slice through 3/4 inch hardwoods. The human eye (at least these 40+ year old human eyes) can barely see the individual teeth. Which got me pondering as to how they manufacture and sharpen the blades.
Apparently they’re milled, rather than stamped, but that’s all I know. Anyone knows what processes are used to make something like this?
That depends on the particular blade and manufacturer. Frequently know as fret saw as well as scroll saw blades.
From >Dogpile.com> search for fret saw blades, get this site. <Scroll Saw Blades>
I really can’t imagine them being milled instead of stamped, but it might be. (I’d think that it’d be more likely they were cut out with a laser or water jet cutter.) Best guess, is that they’ve got a computerized machine with a grindstone (can’t imagine an endmill small enough to work, that would last long enough to cut more than a few teeth), which grinds the teeth onto the blade edge. The only other possibility I can think of off the top of my head, is that they have something like a knife (for lack of a better term) which drops straight down and cuts the metal such that it forms the teeth.
FYI They are first milled, ground, or formed THEN hardened.
Yeah, I figured as much, but since I’ve got no clue as to exactly what hardening process they would use (i.e. do they run a flame just over the teeth, or do they heat the whole blade up, or zap it with a laser, or induction harden), I figured I’d just cut my losses and go with the gibberish I had, rather than add more to it. 
Well, that doesn’t say anything about how they are made, although I note that at least one line of blades is described as “Precision Ground”. Which raises even more questions – what kind of grinder do you use on something that small? Almost microscopic diamond tipped wheels?
Unless you worked for the manufacturere you may never know. Some manufacturing process are propietary secrets. Most of the shaping done by carbide and/or diamond cutters, hardening done by induction and fast cooling. Big band saw blades 1 to 1-1/2 wide with varying pitches have only the tips of the teeth hardened by a similar method. The hard tooth does the cutting while supported by the sofer and flexible band. Not likely to find the fine details of actual manufacture.