Calculating the k6 fundamental deviation and its limits

On the drawing of a precision pulley locating shaft, the seat is dimensioned ⌀30 k6. The turner wants the exact numerical limits. Position k6 gives a transition fit: paired with an H7 hole, it can produce either a very small clearance or a very small interference.

Values and calculation of the k6 deviation to ISO 286

Nominal range (mm)	IT6 (µm)	Lower deviation ei (µm)	Upper deviation es (µm)	Limits at the range’s upper size (mm)
Over 6 up to 10	9	+1	+10	10.010 / 10.001
Over 10 up to 18	11	+1	+12	18.012 / 18.001
Over 18 up to 30	13	+2	+15	30.015 / 30.002
Over 30 up to 50	16	+2	+18	50.018 / 50.002

All values are given for the reference environmental conditions of 20 °C.

Deviations for a k6 shaft

For position k, the lower deviation ei is slightly positive (e.g. +2 µm for the 18–30 mm range). The upper deviation es is es = ei + IT6 = +2 + 13 = +15 µm (+0.015 mm). To compare with other fits, see the g6 fundamental deviation and its limits.

Inspection limits for a ⌀30 k6 shaft

Max size = 30.000 + 0.015 = 30.015 mm. Min size = 30.000 + 0.002 = 30.002 mm. The shaft is accepted if its measured diameter lies between 30.002 mm and 30.015 mm.

Machining example and metrology verdict

A ⌀30 k6 shaft is measured with a micrometer at 20 °C. Reading: 30.018 mm. 1. Allowed limits: [30.002 mm; 30.015 mm]. Verdict: the part exceeds the upper limit by 3 µm. The shaft does not conform.

Shop-floor pitfalls with the k6 position

The first pitfall is confusing k6 with j6. The second is forgetting the possible interference at assembly. The third comes from measurement drift with temperature. To automate your tolerance calculations, discover our automatic ISO 286 detection tools.