A tolerance is a permitted variation, not a generic promise attached to “sheet metal.” Cut features, bend angles and dimensions across several bends have different error sources.
| Dimension | Important contributors |
|---|---|
| Hole diameter in flat stock | Cutting process, kerf, burr, stock thickness |
| Hole-to-hole in one flat face | Cut path and machine positioning |
| Flange angle | Springback, material variation, tooling and setup |
| Hole across a bend | Flat location plus bend position and angle |
| Overall multi-bend width | Accumulated bend and flange variation |
Angle error becomes position error
For a flange of length L, a small angular deviation ε in radians produces a tip displacement of approximately Lε. At L = 100 mm and ε = 1° = 0.0174533 rad, the displacement is about 1.745 mm. This is an illustrative geometric sensitivity, not a claim that every shop holds ±1°.
A longer flange can therefore require more careful angular control even if the flat-cut dimensions are unchanged. Use the actual datum scheme and geometry for a complete analysis; not every flange tip moves in the same measurement direction.
Specify the functional requirement
Locate critical holes from useful datums, identify mating interfaces and distinguish dimensions measured before and after forming. Avoid tightly controlling every nonfunctional edge merely because the CAD model has many decimal places. For an assembly gap, calculate the contributing tolerance chain rather than assuming each part’s nominal size will occur.
Discuss achievable capability with the selected fabricator for the actual material, thickness, tooling and batch. Published supplier guidelines apply to their stated conditions and may separate single-bend features from dimensions spanning multiple bends.
Inspection needs a defined state
Specify whether dimensions are checked free-state, restrained in a fixture, before coating or after coating. A flexible part can change shape under measurement pressure. Agree on datum contact and inspection method for critical features. If a tolerance cannot be met economically, revise the design or process with approval; do not quietly widen the drawing limit.
Supplier reference: compare like dimensions
Protolabs’ tolerance article separates same-surface and multi-surface dimensions. Selected published examples are shown below. They describe that supplier’s guidance; they are not an ISO general-tolerance class or an MfgWorkbench manufacturing guarantee. The article does not give a thickness qualification beside each row, so obtain confirmation for your actual stock and geometry.
| Published feature/context | Stated tolerance |
|---|---|
| Hole-to-hole on one surface | ±0.005 in (approximately ±0.13 mm) |
| Edge-to-hardware on one surface | ±0.010 in (approximately ±0.25 mm) |
| Bend-to-hole, same-surface chart | ±0.015 in (approximately ±0.38 mm) |
| Illustrated box holes separated by four bends | Article’s case study: ±0.030 in linear and 1° per bend angular stacking |
Use the original diagrams when matching a feature: the phrase “bend-to-hole” alone is not enough to identify its datum and dimensional path. Do not sum rows indiscriminately or apply a non-cumulative chart value once for every bend.
Turn capability information into a fit check
In an invented one-dimensional fit example, a hole center can move ±0.38 mm relative to its datum and its mating pin center ±0.13 mm. Worst-case relative offset is 0.51 mm. A nominal 0.40 mm radial clearance would not cover that positional stack even before size variation is included. This is a geometry calculation, not a recommended clearance or a GD&T position-tolerance conversion.
Define which surfaces establish the datum and whether the flexible part is restrained during inspection. Check coating and hardware installation stages as well. If the stack is unacceptable, evaluate a slot, floating hardware or a revised datum scheme with the designer. Use the tolerance stack-up calculator only after defining the actual signed dimension chain.
Content updated October 8, 2026. Sources and numerical examples are explained above; examples are not production test results. Editorial method · Report a correction.
References and verification
Original explanations and worked examples by MfgWorkbench. Sources below support the stated concepts or selected reference data; they do not certify every example or a production application.
For a correction, send the page URL, the affected value and supporting documentation through our contact page.