Spindle hours are the single most important indicator of a CNC machine’s mechanical condition — more important than the build year, more important than the exterior. Anyone buying or selling a CNC machine needs to know what spindle hours mean.
What spindle hours measure — and what they don’t
Spindle hours are a count: how long the main spindle was powered and rotating — with or without load. That’s the best available proxy for mechanical wear, but it’s not a direct measurement of the spindle’s condition.
What spindle hours show: The cumulative operating time of the spindle bearing system. What spindle hours don’t show: Whether the bearings were well or poorly maintained. Whether collisions occurred. Whether the spindle ran under normal operating load or idle.
That’s why spindle hours should always be read in context — alongside the maintenance history, the spindle test report (if one exists), and the machine’s visible condition.
Thresholds by machine class
The percentages in the following tables are guide values from our valuation practice and also the calculation assumptions of our residual value calculator — not market data and not asking prices.
Premium milling machines (Hermle, Röders, Mazak Variaxis)
| Spindle hours | Status | Price impact |
|---|---|---|
| Under 5,000 h | Very good — nearly like new | +10 to +15% |
| 5,000–10,000 h | Good — normal operation | 0 to −5% |
| 10,000–15,000 h | Acceptable — inspection recommended | −10 to −20% |
| 15,000–25,000 h | High — spindle test report mandatory | −20 to −35% |
| Over 25,000 h | Very high — assess risk | −35 to −50% |
Standard machines (DMG MORI, Mazak Standard, Okuma LB-EX)
| Spindle hours | Status | Price impact |
|---|---|---|
| Under 5,000 h | Very good | +8 to +12% |
| 5,000–8,000 h | Good | Reference (0%) |
| 8,000–15,000 h | Normal | −12 to −22% |
| 15,000–20,000 h | High — inspection needed | −25 to −40% |
| Over 20,000 h | Very high | −40 to −55% |
Grinding machines (Studer, Blohm, Kellenberger)
Grinding spindles have tighter tolerance windows and run at higher speeds — the thresholds are correspondingly lower.
| Spindle hours | Status |
|---|---|
| Under 5,000 h | Very good |
| 5,000–8,000 h | Good |
| 8,000–12,000 h | Inspection recommended |
| Over 12,000 h | Spindle inspection mandatory |
The spindle test report — and why it’s worth money
A spindle test report, issued by a service technician from the manufacturer or a specialized spindle service company, typically includes:
- Runout error: Measured in µm at the spindle holder and at the end of a test mandrel. Typical: < 1.5 µm for a very good spindle, < 3 µm for an acceptable one.
- Bearing temperature: Measured after 30 minutes of running under typical load. Limits are manufacturer-dependent.
- Vibration amplitude: In mm/s, shows imbalance or bearing wear.
- Noise character: A qualitative judgment from the technician.
This report can offset a high hour count: if a machine with 20,000 hours shows a runout error under 2 µm in the report and a clean bearing temperature, it’s worth more than a machine with 10,000 hours, no report, and unknown noise.
In practice, a current spindle test report can make a noticeable price difference on premium machines.
When spindle hours matter less than the build year
There are cases where the build year is a more important value factor than spindle hours:
Outdated control generation: A machine with 5,000 spindle hours and a Windows XP-based CNC from 2005 is worth less than a machine with 15,000 hours and a current Siemens 840D SL from 2015. The control is the utility driver — and while a spindle is mechanically repairable, a control isn’t quite so easy to replace.
Design progress: Newer machine models often offer significant precision and stability improvements (DMG MORI monoBLOCK versus older designs, for example). A 2012 model with 8,000 hours can be worth less than a 2018 model with 12,000 hours, simply because the newer design is better.
Reading spindle hours — a quick guide
Heidenhain TNC 640/530: MOD key → machine data → operating times. Spindle operating hours listed separately from total operating hours.
Siemens 840D SL: Diagnostics → operating hours → spindle operating hours.
FANUC 30i/31i: System → F → operating times → spindle operating time (a separate entry under machine control time).
Mazak MAZATROL: Machine overview → diagnostics → operating times.
If you want to know what your machine is concretely worth given its specific spindle hours, send us the make, model, build year, and the hour readings — initial assessment.
The tables above are also the basis for the CNC machine residual value calculator — enter machine class, build year, and spindle hours to read off the range.