Engineering · Cost

Tolerance vs cost — the ladder.

Eight tolerance planning tiers with candidate processes and example applications. No universal cost ratio follows from tolerance alone; the feature, setup, material, quantity and measurement plan govern the quote.

Loosest tier

0.030″

Feature-specific quote

Common precision

0.001″

Feature-specific quote

Tight precision

0.0005″

Feature-specific quote

Jig-grind class

0.0001″

Feature-specific quote

Interactive Reference

Tolerance Cost Curve Analyzer

These ordinal tiers are not cost indices, measured TPM capability or production forecasts. Inspection descriptions are considerations, not mandatory methods or sampling plans.

Ordinal Planning Tiers Tier 1

0.030" (Coarse) 0.002" (Standard Precision) 0.0001" (Jig-Grind)

Active Limits 0.030″ (0.76 mm)

Production Process Standard milling, sawing

Part Scrap Risk 1% (Negligible)

Metrology & Inspection Level Standard caliper / line check

Example Process Equipment

Can be run on standard manual or 3-axis mills with minimum setup overhead.

Standard CNC

Tier	Tolerance	Cost vs baseline	Process	Typical features
Tier 1	0.030″ (0.76 mm)	1	Standard milling, single-pass turning, sawing	Bracket envelopes, weldment blanks, non-mating clearances
Tier 2	0.010″ (0.25 mm)	2	Standard CNC, no special tooling	Most general structural features, clearance holes, blank dimensions
Tier 3	0.005″ (0.13 mm)	3	Standard CNC with tighter QC	Mounting bores, dowel-pin holes (clearance), fastener spotfaces
Tier 4	0.002″ (0.05 mm)	4	Precision CNC, in-process probing	Bearing fits, sliding fits, locating features, mating surfaces
Tier 5	0.001″ (0.025 mm)	5	Glass-scale machine, CMM verification	Precision bushing IDs, locating dowel holes, optical mounting interfaces
Tier 6	0.0005″ (0.013 mm)	6	Makino-class precision mill, careful thermal management	Press-fit interfaces, gauge surfaces, metrology fixtures
Tier 7	0.0002″ (0.005 mm)	7	Wire EDM or grinding for finishing	Bearing races, optical alignment surfaces, gauge masters
Tier 8	0.0001″ (0.0025 mm)	8	Wire EDM, jig grinding, lapping	Tool-and-die work, ultra-precision metrology, quantum/cryo flexures

Why the cost climbs so fast

It’s not just the cut.

Tighter tolerance forces tighter machine selection.

A 0.005″ feature runs on any mill. A 0.0005″ feature needs a Makino-class precision machine with glass scales — different machine, different rate, different schedule.
Inspection needs a measurement plan.

Measurement method, resolution, uncertainty and sampling depend on the characteristic and quality plan. A CMM is not automatically adequate or required at a particular tolerance.
Yield needs process data.

Yield depends on the process distribution, measurement system and feature requirements. No scrap-rate percentage can be inferred from tolerance alone; use measured capability and production data.
Setup time grows with tolerance.

Setup time depends on datum strategy, workholding, thermal stabilization, measurement and trial cuts. No fixed setup duration follows from a tolerance value.
Process changes — sometimes you have to.

Small internal radii or demanding form requirements may favor EDM, grinding or another finishing process. Material conductivity, access, geometry and demonstrated capability determine the options; a tolerance alone does not mandate one process.

Practical guidance

Three rules for not overspending on tolerance.

1. Tolerance only what mates or measures.

Bearing fits, alignment surfaces, sealing surfaces — those need precision. Edges of a bracket, hole locations far from a datum, cosmetic features — those don’t. Apply tight tolerance only where it matters functionally.
2. Use ISO 2768 or default-tolerance blocks.

Unnecessary tight callouts can add setup and inspection work. Use a reviewed general-tolerance scheme and explicit requirements on functional features; savings require a feature-specific quote.
3. Specify GD&T relative to actual datums.

A 0.001″ positional tolerance referenced to the right datums is much cheaper than 0.001″ on each X/Y/Z dimension. GD&T allows the machinist to optimize stack-up; per-axis tolerance forces them to hit each independently.

Keep exploring