What the tool does
Spreadsheet stacks lose signs, mix up upper and lower limits and hide the statistical assumptions. The tool keeps each link's direction and limits and shows every method side by side.
- Chain: each link with direction, nominal, signed upper and lower deviation, distribution (normal, uniform, triangular), Cp and mean shift; a loop diagram; paste from a spreadsheet.
- Methods: worst case, RSS (with the Bender factor 1.5 if you want), statistical ± 3σ with mean shifts, and Monte Carlo with a sample count and seed you choose.
- Against the limits: yield, ppm outside, Cp and Cpk of the result, and a warning when only statistics keep the design inside.
- Contributions: each link's share of the worst case and of the variance, so you see which tolerance to tighten.
- ISO fits: H holes and e, f, g, h, js, k, m, n shafts from the published ISO 286 formulas, the fit type and clearance, with fields for the exact values from your table; send hole and shaft to the chain.
- Report: a PDF with the chain, the loop diagram, the results, the contributions and the histogram, a workbook whose results are formulas, and CSV.
How to use it
- Enter the dimensions of the loop in order, + where they add to the gap and − where they subtract.
- Set the limits on the result, for example a lower limit of 0 for a gap.
- Choose distributions, Cp and mean shifts where you know them, and run Monte Carlo.
- Read the contributions, change tolerances, and export the report.
What is built in
The formulas only. ISO 286 limits are computed from the published formulas for IT grades and fundamental deviations; the standard's own tables are copyrighted and round some values, so the tool labels its fit limits as approximations and takes the exact values if you enter them.
How it was checked
Before every release the engine is run on published examples: housing 25 ± 0.10, shaft 18 ± 0.08 and spacer 6.5 ± 0.05 give a gap of 0.27 to 0.73 worst case and ± 0.137 RSS with contributions 43.5 / 34.8 / 21.7 % and 52.9 / 33.9 / 13.2 % (turn2engineering); three links of ± 0.05 give ± 0.15 and ± 0.0866; three sheets of 0.075 ± 0.005 against 0.225 ± 0.009 keep 99.8 % centred and about 70 % with a 1.5σ shift (Five Flute); 25 H7/g6 gives a hole of 25.000 to 25.021, a shaft of 24.980 to 24.993 and a clearance of 0.007 to 0.041 mm. Monte Carlo is checked against the analytical σ.
Limits
The tool handles one-dimensional chains with independent links. It does not model 3D assemblies, geometric tolerances beyond simple ± equivalents, or correlated dimensions. Fits cover H holes and the common shafts; interference shafts p to zc are not included.
Last checked 2026-10-20