Tolerance stacks decide whether a Divine Precision assembly fits on the first try or burns hours in rework. Reading the stack early — before the drawing reaches the shop floor — keeps fits intentional and machining economical.
When to review a tolerance stack
A tolerance stack is worth reviewing whenever parts mate, slide, press or seal. Gaps that look fine on a single drawing often disappear once diameters, positions and surface finishes accumulate across the assembly.
Review the stack when your project involves:
- Mating diameters, bores and shafts with press, slip or transition fits
- Multi-part assemblies where position and flatness interact
- Sealing faces, O-ring grooves and gasketed joints
- Features that will be inspected with CMM or functional gauges
- Drawings converted from 3D models without a manufacturing review
- Cost targets that leave little room for scrap or selective assembly
At Divine Precision we walk through the stack with your design team, highlight the drivers, and suggest where opening a tolerance or changing a datum saves cycle time without risking function.
What a clear stack review delivers
1. Functional fits, not paper fits
We map each contributor to the fit you care about so nominal numbers are not chasing millimetres that never touch.
2. Datum strategy that matches the process
Primary datums are chosen for how the part is held and measured, not only how it was modelled.
3. Process capability in view
Swiss turning, CNC milling and grinding each hold different realities; the stack should reflect that.
4. Inspection plan alignment
Critical dimensions get a method — CMM, gauge or attribute — before the first article runs.
5. Cost levers called out
Tight callouts that do not affect function are candidates to open or move to a note.
6. Change traceability
Agreed revisions land on the drawing so purchasing and quality see the same target.
7. Faster first-article release
Fewer surprises at FAI mean shorter path from sample to production.
Typical contributor ranges we discuss
The table below shows the kinds of contributors we capture in a stack review. Values are indicative for precision machining discussions, not a substitute for your GD&T.
| Contributor | Typical discussion range | Notes |
|---|---|---|
| Diameter / shaft | ±0.01 – ±0.05 mm | Depends on bearing or bushing class |
| Positional (true position) | Ø0.05 – Ø0.2 mm | Tied to datum scheme |
| Flatness / parallelism | 0.02 – 0.1 mm | Sealing and mounting faces |
| Surface finish (Ra) | 0.4 – 3.2 µm | Impacts fit and sealing |
Treat the stack as a living document: update it when materials, suppliers or inspection methods change, not only when a fit fails in assembly.
Once the critical chain is agreed, we lock it into the control plan and quote to that intent — so shop-floor decisions stay aligned with design.
Before you release the drawing
Share the assembly context, preferred datums and any must-hold interfaces. PDF plus STEP is enough to start; full GD&T drawings accelerate the review.
Send the package to Divine Precision and we will return a short stack summary with recommended callouts, risk notes and a machining approach that matches your volume.
