Spindle Speed and Feed for Micro Tools: A Practical Setup Guide
Small tools fail from too much speed, not too little. This note covers practical spindle speed, feed per tooth, chip load and how to reduce them safely when the first trial goes wrong.
The instinct with small tools is to run them faster, because edge speed has to be high. In practice most micro tool failures come from speed and feed that are too aggressive for the rigidity available, and the fix is almost always to reduce rather than increase.
Establish edge speed first
Calculate the required surface speed from the workpiece material and tool material, then convert to RPM from the tool diameter. Because RPM scales inversely with diameter, a Ø 0.1 mm tool reaches the same edge speed at ten times the RPM of a Ø 1.0 mm tool. Confirm the spindle can actually reach it — many machines nominally reach speeds they cannot sustain under load.
Start conservative
For a first trial, run at roughly 60–70% of the calculated edge speed and let the tool tell you what it wants. If chips are clean and evacuation is good, increase in steps. If the chips are being compacted or burned, reduce before you increase.
Feed per tooth
Feed per tooth should be small enough to cut rather than rub, and large enough to let the chip escape. For a two-flute micro end mill in hardened steel, think in terms of a few microns per tooth per flute, then adjust from observed behaviour. Rubbing produces built-up edge within seconds and destroys the coating.
Interrupted cuts
In interrupted cutting the tool sees a shock on every engagement. Reduce the feed and allow the machine to decelerate on entry. For a contouring operation, prefer a finer step-over with more passes over a single aggressive one.
What to check on a failed trial
- Burned chip — reduce speed or improve coolant.
- Built-up edge — the tool is rubbing; reduce feed per tooth and check the coating.
- Wandering hole — the spindle or collet is the problem, not the drill; check runout.
- Chatter marks — reduce feed and increase rigidity.
- Poor surface finish — usually step-over on a ball nose, or chip load too high.
Send us your numbers
When you ask for a tool, send the machine, spindle, collet and the speeds you run. A tool specified against your real rigidity will outperform one specified against a datasheet ideal.
Does this apply to your part?
Send the drawing and we will tell you, not guess.
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September 4, 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.
