David Krause14.1 The difference
A machine is switched on as long as it is occupied — including during setup, gauging and tool changes. The spindle turns only part of that time. In the reference company that is 2,647 of 3,393 productive hours, i.e. about 78 percent.
| Cost element | spindle time | setup time | Reasoning |
|---|---|---|---|
| Electricity | 80 % | 20 % | main drive vs. base load and control |
| Coolant | 90 % | 10 % | high pressure while cutting, otherwise base circulation |
| Compressed air | 70 % | 30 % | blowing and cooling active |
| Tool wear | 100 % | 0 % | no contact without cutting |
14.2 Costing rate and spindle rate
Both rates are correct — they answer different questions. The costing rate spreads all costs over the productive hours and is used for quotations. The spindle rate shows what a value-adding hour really costs and is steering information.
| View | Basis | Energy | Tooling | Total rate |
|---|---|---|---|---|
| Costing rate | 3,393 h | €8.97/h | €5.45/h | €46.37/MH |
| Spindle rate analysis figure | 2,647 h | €11.50/h | €6.99/h | €59.44/h |
| Difference | — | +€2.53/h | +€1.54/h | +€13.07/h |
Costing still uses €46.37/MH. The spindle rate of €59.44 is not an alternative to it but a diagnostic figure: it shows how expensive unused spindle time is. Whoever mixes the two rates charges the costs twice.
14.3 What the split does to the price
An order with 30 minutes of setup and 90 minutes of spindle time is valued differently under the correct method: the setup costs come out lower because they carry no tool costs, the spindle costs correspondingly higher.
On balance, large-series parts with long spindle time become 2 to 4 percent more expensive, small-series changeover parts with much setup time 3 to 6 percent cheaper. That is exactly the signal you want: setup costs time but no tooling — and a company that makes small series should not be penalized for it.
14.4 Effect on the machine hour rate
Costing view (all costs over productive hours — the rate for the quotation) and analysis view (all costs per spindle hour — the causation figure) on the 5-axis machining center. The spindle view is steering information; costing still uses €46.37/MH.
| View | Hour basis | Energy | Tooling | Total rate |
|---|---|---|---|---|
| Costing rate (productive hours) | 3,393 h | €8.97/h | €5.45/h | €46.37/MH |
| Analysis figure (per spindle hour, 78 %) | 2,647 sp-h | €11.50/sp-h | €6.99/sp-h | €59.44/sp-h |
A value-adding spindle hour really costs €59.44 — the difference from the €46.37 shows how much the 22 % idle time raises the cost of productive time.
14.5 OEE measurement in practice: four maturity levels
| Level | Method | Data source | Effort / accuracy |
|---|---|---|---|
| 1 | estimate from experience | supervisor judgment, benchmark values | ★☆☆☆ · sufficient for initial setup |
| 2 | shop-floor feedback (manual) | time stamps per order | ★★☆☆ · SME without MES |
| 3 | spindle monitoring | spindle-current sensor / NC data | ★★★☆ · precise spindle time |
| 4 | MES / IIoT connection | machine data in real time | ★★★★ · best accuracy, highest effort |
Most companies sensibly start at level 1 or 2 — a rough OEE from experience values is better than none. The jump to level 3 pays off as soon as spindle time is needed for tool cost allocation (Chapter 15).
