A micro drill is only the drive — what actually happens to the material is decided by the accessory in the collet. Burrs of various profiles, grinding and engraving heads and cutting discs all fit there, and the shape of the tool determines the result: a ball head hollows out a recess, a cylindrical one opens a hole to a straight wall, a tapered one breaks an edge and countersinks a mouth, while fine diamond points serve for engraving and refining a shape.
These hollow material out into a recess with a rounded bottom. They are used inside cowlings, when thinning a wall and for organic shapes in filler. Work in thin passes — a ball head cuts quickly and a hollow appears in a wall sooner than you expect.
These open a hole out to a straight cylindrical wall and flatten its bottom. They suit seats for magnets, pins and tubes, where a part has to sit exactly and square.
These break an edge, countersink a mouth and create a tapered transition. They earn their place at gun muzzles and exhausts, where the rim should look thin — the countersink creates the impression of a tube wall.
Very fine tools for engraving, levelling small blemishes and working hard materials. They cut abrasively, so they remove material gradually and stay easy to control.
Thin cut-off and grinding discs part material where a saw will not fit and true an edge at the same time. With these it goes double that the work must be clamped and the eyes protected, because a disc shatters when it binds. Use them in short touches and let the material cool, especially styrene, which melts under heat.
The most important figure is shank diameter — the accessory has to fit the collet of your micro drill, otherwise it is badly held and runs out of true. The second is speed: low on styrene so the material does not melt, higher on hard compounds with a light feed. The third is clamping the work, because a rotating burr can snatch a loosely held part out of your hand. Use a vice from stands and clips.
If all you want is a hole with no further shaping, a tool from pin vices will do the job.
