TolChain: Tolerance Stack-up

TolChain chains drawing dimensions and tolerances together so you can check whether an assembly gap or protrusion stays within spec — a tolerance stack-up analyzer for your phone.
Analyze the same dimension chain three separate ways — Worst Case, RSS and Monte Carlo — and compare the results. Every calculation runs on your device; your dimensions and projects are never sent to a server.

■ Method 1 — Worst Case
· Minimum and maximum assembly value with every dimension at its tolerance limit
· Margin to the lower and upper spec limits (mm) and a pass/fail verdict
· Tolerance-width contribution: which dimension takes up most of the worst-case band
· Limit values per dimension, with +/− direction applied

■ Method 2 — RSS (root sum square)
· Mean ±kσ range (±2σ, 3σ, 4σ, 6σ) assuming independent dimensions
· Estimated mean, standard deviation σ and spec margins
· Cpk (normal approximation when all inputs are normally distributed)
· Variance contribution, sorted so you know which tolerance to tighten first
· Asymmetric tolerances use the midpoint of the tolerance zone as the mean; normal or uniform distribution per dimension

■ Method 3 — Monte Carlo (3D variation simulation)
· 10,000 to 1,000,000 random assemblies, reproducible with a seed
· Normal, uniform and symmetric triangular distributions
· Histogram, estimated defect rate (PPM) with a Wilson 95% confidence interval, empirical quantiles
· Simulate your 1D chain as-is, or run a 3D model
· 3D: position (X, Y, Z) and rotation (Rx, Ry, Rz) tolerances of two rigid parts, gap or distance between measurement points, conservative 3D bounds and per-input sensitivity

■ Enter tolerances from pictures
· 24 models with 48 illustrations: housings, bearings, bolts, connectors, PCBs, lenses, battery cell stacks and more
· Tap a colored symbol on the assembly or exploded view to jump to that dimension
· Repeated parts are expanded into individual dimensions by quantity

■ Data and reports
· Auto-saved on this device, plus one automatic backup per day
· Full backup and restore (free) — move projects to and from the PC web version as JSON
· PDF / print reports and Monte Carlo result CSV
· No sign-in required · English and Korean

■ Free and Pro
Free: Worst Case and RSS analysis, 3D analysis, previews of all 24 models, 8 basic examples, 3 new projects, 30 dimensions, backup and restore
Pro subscription: no ads, all 24 examples (including battery stacks and advanced 3D models), 1D and 3D Monte Carlo up to 1,000,000 runs, 100 dimensions per chain, unlimited projects, unlimited reports and CSV
The free version shows ads, and some features can be used once by watching a short ad. You can also watch an ad for a 24-hour Pro trial.
Cancel anytime in Google Play. Subscriptions renew automatically unless cancelled before the end of the period. Your projects and backups stay even if you cancel.

■ Made for
· Mechanical designers checking housing and cover gaps or shaft and bearing end play
· Process and quality engineers allocating tolerances and estimating defect rates
· Students and new engineers learning the difference between Worst Case and RSS with pictures

■ Good to know
· The 3D feature is TolChain's own two-rigid-body, measurement-point model. It does not connect to or replace commercial tolerance analysis software, CAD (STEP) geometry analysis, GD&T, or contact/deformation analysis.
· The mean of an asymmetric tolerance is modeled as the midpoint of the tolerance zone. Real process means and distributions may differ, so use the results as a reference for design review.
· RSS ranges and Monte Carlo defect rates are statistical estimates, not worst-case guarantees. Zero simulated defects does not guarantee zero defects.
· Illustrations are conceptual and not to scale.

Contact: [email protected]