countersinking

Reference — What angle of countersink do I need? 60°, 82°, 90°, 100°, or 120°?   [2].

holes < ~¼"

The sort of holes that you need a pin vise to drill.

For these, I like to use a rotary tool bit (AKA rotary burr):

• A good setup — use 1) a 60° steel bit [1] [2] [3], followed up with 2) any of these 60° diamond bits.
• Bits might be made out of tungsten carbide, aluminum oxide grinding stone, silicon carbide grinding stone, diamond, (TODO)
• The shape you're looking for is something like a "60 degree cone" or a "beveling chamfer bit"

holes from 1/4" to ~1.5"

These "zero flute" cutters seem to work really well — but only for wood, not metal:

• KEO Cutters [offsite] [offsite]
• HHIP
• My goal is to build a container of my own that's similar to this kind of box.
• (TODO: add more manufacturers. These are variously known as "cross-hole", "Weldon style", or "zero flute" countersink bits.)