Stack
Saved in this browser as you typeChain at 20 °C
Arrows right add, left subtract · band = ± tolerance · circle = zero nominal · click a row to editColour: share of variancelowhigh
Contributors
result = Σ direction × factor × valueImport and export
Method notes
- Sign convention
- Each contributor has a direction (+ adds to the result, − subtracts) and an optional factor, e.g. a lever ratio. Worst case and RSS use each contributor's mean (centre of its zone) and half range
h. - Worst case and RSS
- Worst case is
Σm ± Σh. RSS isΣm ± √Σh², which assumes every tolerance is a centred ±3σ normal process. - Monte Carlo
- Each contributor is sampled from its own distribution. Normal means the tolerance zone is ±3σ about its centre, unbounded, so a few samples land past the worst case. Contribution bars show the share of result variance.
- Thermal expansion
- Sizes are defined at 20 °C (ISO 1). A part at ambient T plus its own ΔT grows by
α·L·(T + ΔT − 20). Fits change clearance byD·(α_hole·ΔT_hole − α_shaft·ΔT_shaft). - Angle and form
- An angular tolerance ±θ moves a point at lever arm L by
L·tan θ. A geometric zone t over length Lz (perpendicularity, parallelism) is treated as a tilt of up tot / Lz. ISO 2768-1 angles use the shorter leg length. - Fits, pins and play
- Clearance is diametral:
hole − shaft. Floating means the part can sit anywhere within ±½ clearance (uniform). Pushed to one side gives +½ clearance, e.g. under gravity or a spring. Where clearance is zero or negative (transition or interference) the float is zero. - ISO 286 codes
- Deviations are computed from the ISO 286-1 fundamental deviation rules for 0–500 mm, letters D–H, JS, K, M, N, P, R, S (holes) and d–h, js, k, m, n, p, r, s (shafts), grades IT4–IT13. Check critical fits against the published tables, which list a few special cases. Rolling bearing ring tolerances (ISO 492) go in as plain deviations.