How to Read ISO Technical Drawings - Complete Guide
Learn the basics of reading technical drawings according to ISO standards. Discover how to interpret dimensions, tolerances, and machining symbols.
Technical drawings are the fundamental communication tool in the mechanical industry. The ability to read them correctly is crucial for CNC technologists, machine operators, and designers. In this guide, we will present the basics of reading drawings according to ISO standards.
Projections and Views
A technical drawing represents an object using orthographic projections. Three main views are typically used: front view (main), top view, and side view. Each view shows a different perspective of the part, allowing for complete understanding of its shape. The ISO standard defines two projection methods: European (first angle) and American (third angle). In Europe, the first angle projection method is most commonly used.
Dimensioning According to ISO
Proper dimensioning is key to understanding a drawing. Dimension lines should be placed outside the object outline and terminated with arrowheads or oblique strokes. Dimension values are given in millimeters (without units). Diameters are indicated with the Ø symbol, radii with R. Angular dimensions are given in degrees. It's important to distinguish between nominal dimensions and dimensions with tolerances.
Dimensional Tolerances
Tolerances define the permissible deviations from the nominal dimension. They can be specified as numerical values (e.g., 50±0.1) or as ISO tolerance classes (e.g., H7, g6). The ISO tolerance system is divided into classes from IT01 to IT18, where lower numbers indicate higher precision. For fits, a combination of hole tolerance (uppercase letters) and shaft tolerance (lowercase letters) is used.
Surface Roughness
Surface roughness defines the quality of surface finish after machining. The most commonly used parameter is Ra (arithmetic mean deviation of the profile). Roughness symbols are placed on surfaces requiring specific quality. Typical Ra values for cutting operations are 0.8-6.3 μm, for grinding 0.2-1.6 μm.
Heat Treatment Designations
Drawings may contain requirements for heat treatment: hardening, carburizing, nitriding, etc. These designations are usually found in the title block or as technical notes. Most commonly, the required hardness (HRC, HB) and the depth of the hardened layer are specified.
Summary
Reading technical drawings is a skill acquired through practice. Key aspects include understanding symbols and designations according to ISO standards, knowledge of the tolerance system, and the ability to interpret quality requirements. Our Technolog CNC system helps automatically analyze drawings and extract the most important technological information from them.
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