Learn ISO 14405-1 and how linear sizes differ from geometric tolerances. Understand LP and GG symbols to avoid common GD&T interpretation errors.
Overview of ISO 14405-1
ISO 14405-1 defines how linear sizes are specified and interpreted in engineering drawings. It clarifies the difference between size specifications and geometric tolerances, introducing concepts like local size (LP) and global size (GG).
This standard is critical because many engineers incorrectly assume size controls geometry, leading to misinterpretation and manufacturing issues.
Core Principle
Linear Size Specification
Defines how size dimensions are applied to features
Ensures clarity in dimensioning
Local Size (LP)
Measures size at a specific cross-section or point
Controls variation at a local level
Global Size (GG)
Measures overall size across the entire feature
Controls variation at a local level
Core Concepts
Size measured at individual sections of a feature.
Purpose: Size measured at individual sections of a feature.
Size does not automatically control form or orientation.
Purpose: Size does not automatically control form or orientation.
High-Cost Errors
Confusing Size with Geometry
Assuming size tolerances control form leads to rejected or non-functional parts.
Ignoring LP/GG Symbols
Misinterpreting local vs. global size causes incorrect inspection results.
How to Apply ISO 14405-1
01
Define Size Requirements
02
Choose LP or GG
Decide whether local or global size is functionally required.
03
Avoid Assumptions
04
Apply with ISO 8015
05
Validate Measurement Methods
AI Drawing Validation & Audit
Automated Compliance Checks
Reduce Revision Cycles by 40%
Comparison & Related Standards
ISO 14405-1
Focuses on size specification and interpretation.
ISO 1101
Defines geometric tolerances like form, orientation, and position.