Micro Drill Selection: Diameter, Depth, Material and Point Geometry
Choosing a micro drill is a four-variable problem: diameter, hole depth as a multiple of diameter, workpiece material and point geometry. Getting the interaction right is what separates a tool that works from one that merely exists.
A micro drill is selected the same way any drill is — by the combination of material, depth and speed — but at small diameters the margins are far thinner and the interactions between variables matter more.
Diameter sets the limits, not the speed
Below about a millimetre, a drill's cutting edge speed is easy to achieve and hard to use. Small diameters deflect more, absorb heat faster and have less stock to fail before the tool breaks. The practical starting point is therefore to confirm the spindle can reach the required edge speed and then decide how much of it you will actually use.
Hole depth as a multiple of diameter
The ratio of depth to diameter is the single most important selection variable. A Ø 0.1 mm hole drilled to 3× diameter is a routine operation. The same hole at 10× diameter is a different tool entirely, because chips must travel further before they clear.
- Up to 3× — most micro drills perform well.
- 3–6× — prefer a higher helix angle and more flutes for evacuation.
- 6–10× — consider spiral flute geometry, lower speed, interrupted cuts.
- Above 10× — discuss the process before ordering; a different tooling strategy may be more reliable.
Workpiece material decides the coating
Match the surface to the chip, not the other way round.
- Hardened steel, stainless, titanium — TiAlN or AlCrN.
- Aluminium, copper — DLC or uncoated with a generous helix angle.
- CFRP, graphite — DLC, to reduce friction and delamination.
- Brass, soft steel — uncoated HSS or carbide is often sufficient.
Point geometry
The point angle controls entry behaviour. A sharper point (118°) enters more cleanly in hardened material; a larger web and steeper point tolerate more runout but remove material differently. In practice the point form should be specified together with the tolerance on runout, because a sharp point on a misaligned spindle will wander on entry.
What to send us
For a quotation we need: nominal diameter, depth as a multiple of diameter, workpiece material and hardness, machine and maximum spindle speed, coolant arrangement, and target production volume. If an existing tool is underperforming, send one — comparing against a known reference is faster than iterating blind.
Does this apply to your part?
Send the drawing and we will tell you, not guess.
Related notes.
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August 23, 2026What we make.
Micro drills from 0.03 mm, in standard, helical, step, left-hand and aluminium-grade geometry. Every entry is a live, shipped configuration.
End mills from 0.1 mm across single and double flute, helical and straight, ball and flat geometry, with aluminium- and acrylic-dedicated lines.
Single and double flute chamfer mills, ball-tip finishing cutters, flat-bottom finishing cutters and extended-reach versions for deep features.
