The escalation rule
A tolerance error caught at design costs ~$1 to fix. Caught in production it's ~$10; once it reaches the customer, ~$100 — the classic 1-10-100 cost-of-poor-quality curve, and far steeper in regulated industries.
◇ 1D Stack-Up · Worst-Case · RSS · Monte Carlo
Tolerance stack-up analysis,
done the way you'd do it on
paper.
Professional-grade variation analysis for the missing middle — the engineers stuck between fragile spreadsheets and $25,000-a-seat simulation suites. It reads your drawings, parses the GD&T, and is fast enough to use before you release the package.
Designed for the
PTC Onshape Ecosystem
80%Time Reduction (vs. manual Excel)
90%+Extraction Accuracy (from 2D PDFs)
Onshapenative CAD import
SHA-256audit-ready reports
01 · Why it matters
Improper tolerancing is a silent profit killer
In precision work — aerospace, medical, robotics — variation is inevitable. How you analyze it decides whether parts assemble, what they cost to machine, and how late you find out.
The over-tolerancing tax
To dodge failures, engineers default to tight tolerances. That pushes parts from standard milling into secondary grinding — quietly inflating machining cost on features that never needed it.
Analysis done too late
Stack-up is often deferred until the design is frozen, when corrective changes are hardest and most expensive. TolFlow makes it cheap enough to run while you're still dimensioning.
$1 design──┤ $10 production──┤ $100 field ▲ cost of catching it late
02 · The market
The tooling left a hole in the middle
Tolerance analysis is bifurcated: free but disconnected on one end, powerful but priced for specialists on the other. Most small-to-medium teams get neither.
| Tool | Tier | Analysis | CAD link | Price | Key limitation |
|---|---|---|---|---|---|
| Microsoft Excel | Universal | 1D, manual | None | In M365 | Transcription errors; breaks on every ECO |
| Five Flute calculator | Startup | 1D, web | None (manual) | Free | No bidirectional CAD link |
| SolidWorks TolAnalyst | Mid | 1D + basic 3D | SW native | In SW Pro/Premium | Clunky; struggles with angles & radii |
| Sigmetrix EZtol | SMB | 1D standalone | Reads PMI | ~$125 / mo* | No full 3D kinematic capability |
| ◇ TolFlow | The middle | 1D WC + RSS + Monte Carlo | Onshape-native | Mid-market | Focused on 1D stack-up (by design) |
| CETOL 6σ (Sigmetrix) | Enterprise | 1D / 2D / 3D | SW, NX, Creo, CATIA | ~$10k–25k / seat* | Cost & complexity barrier for SMBs |
| 3DCS Variation Analyst | Enterprise | 1D / 2D / 3D + FEA | SW, NX, CATIA, Creo | ~$8k–25k / yr* | Needs a dedicated variation specialist |
*Enterprise figures are quote-based industry estimates — none of these vendors publish list prices. EZtol price from a public marketplace listing (1-month, single seat). Figures verified 2026-06-30; full sourcing in the project's competitive research notes.
03 · Onshape-native
The first stack-up app built for cloud CAD
PTC's Onshape leads cloud-native CAD, but its App Store still has no dedicated tolerance stack-up or variation app. TolFlow docks straight into that gap.
- Paste an Onshape drawing URL, or launch TolFlow from the Onshape app
- Dimensions and GD&T pulled from structured drawing data — no LLM guesswork
- Refresh after a CAD edit: unchanged dims keep approval, changed ones reset, new ones flag
- Batch-pick additional drawings from the same Onshape document
04 · Capabilities
Built for engineers who have to defend the number
Every result traces back to a source. Nothing is invented.
Worst-case & RSS, side by side
Deterministic worst-case limits for 100% interchangeability, and probabilistic RSS limits when you want to open tolerances for higher yield — from the same loop.
Pareto sensitivity
See the heavy hitters driving your stack so you can loosen non-critical tolerances and cut machining cost where it doesn't matter.
Cpk manufacturability checks
Called a tolerance tighter than the process can hold? TolFlow flags it against standard process-capability data before it reaches the floor.
Monte Carlo simulation
Go beyond closed-form limits — sample each dimension's manufacturing distribution to estimate real-world yield and Cpk for the assembled gap.
GD&T & feature control frames
Reads feature control frames straight off the drawing — ⌖0.1 A B becomes a position tolerance with datums A and B, with datum continuity tracked through the stack.
Annotations, Smart Dimension & BOM
Mark up assemblies and place dimensions Onshape-style — click start, click end, drag to offset. Parts lists and revision history are pulled from the title block.
Collaboration & designer sign-off
An acting-identity model with a reviewer workflow: designers approve dimensions, leave feedback, and every action lands in a timestamped audit log.
Provenance on every tolerance
Each value carries a tag — explicit callout, title-block rule, or a standard like ISO 2768. If a dimension can't be resolved, the engine refuses to guess.
Audit-ready reports
Reports are immutable and SHA-256 checksummed, exported to PDF, DOCX, or XLSX. Recomputation creates a new revision — never a silent overwrite.
Zero-setup, mid-market price
Professional worst-case and statistical stack-ups with none of the setup friction — at a price that fits the shop with neither a spreadsheet wizard nor a six-figure tooling budget.
Review
Verify every dimension on the original drawing
Extracted dimensions are overlaid directly on the source PDF, so you can confirm each one before it enters a loop. Garbage in, garbage out — so the tool pushes back at every step.
Review workflow →
Loop · Analyze
Build the loop, read the result
Define the closed dimension loop, and the engine evaluates the worst-case sum and RSS spread with closure checks — warning you when the nominal chain doesn't reproduce the gap callout.
The math, stated exactly →
Report
Export a signed, traceable report
Every analysis exports to an immutable, checksummed report — dimension tables, provenance tags, the assembly image, and the Monte Carlo histogram — ready for a design review or a regulated quality file.
Traceability →
05 · The pipeline
A linear, seven-step pipeline
Each step has its own screen — and a Help button that opens the matching guide right beside your work.
- 1Create a project
- 2Import drawings
- 3Review components
- 4Link assembly
- 5Build the loop
- 6Analyze WC / RSS
- 7Export report
06 · Walkthrough
End-to-End Workflow Demonstration
Watch the full TolFlow automated pipeline in action.
07 · Pricing
Plans that scale with your precision
Choose the level of analysis and collaboration that fits your engineering workflow.
Free
For hobbyists and individual engineers getting started with tolerance loops.
- 1D Worst-Case & RSS stack-ups
- Onshape-native CAD import
- Vector PDF drawing import
- Core dimension annotations
Professional
For startups and consulting engineers who need advanced statistical yield analysis.
- Everything in Free
- Monte Carlo simulation & yield
- AI-assisted report narratives
- Scanned PDF extraction (OCR/Vision)
- PDF, DOCX, & XLSX exports
Enterprise
For engineering organizations and mid-market OEMs requiring reviewer approval and sign-offs.
- Everything in Professional
- Reviewer sign-off workflows
- Acting-identity reviewer logs
- Revision control & history tracking
- Centralized company templates
- Org-scoped user administration