0.004" micro drill bit - photo

[Toolmaker51]

.004 Yikes.
I made 180 blow mold nozzles, drilled in 4 opposing rows, 44 total holes each. Those were .015 diameter, fastest spindle I could find, only 9000. Not 63,000.
So, I had the lightest touch imaginable for quite some time later.
Fixture used 01 drilled and heat treated for effective drill bushing in favored 10 diameters thickness [.150]. It was positioned one diameter from part, above centerline. The carrier had pin to register in fixture notched to regulate spacing of opposite sides. After 2 rows were done, moved pin to second position. That set other rows halfway between the first. It went remarkably fast; keeping fixture and bushing in place, moving the part instead. Targeting 11 bushings would have been a numbing endeavor.