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ISO 2768m General Tolerances PDF: A Complete Guide for CNC Machining and Sheet Metal Fabrication
If you are a CNC machinist or a sheet metal worker, you know how important it is to follow the correct tolerances for your parts. Tolerances are the allowable deviations from the nominal dimensions of a part, and they ensure that the parts fit and function properly. However, specifying individual tolerances for every dimension on a drawing can be tedious and time-consuming. That’s why there is a standard that simplifies the drawing indications and specifies general tolerances for linear and angular dimensions without individual tolerance indications. This standard is called ISO 2768m.
In this article, you will learn what ISO 2768m is, what are the tolerance classes and ranges, how to apply it to your drawings, and how to download the PDF file of the standard for free.
What is ISO 2768m?
ISO 2768m is an international standard made by the International Organization for Standardization (ISO), which consists of two parts: ISO 2768-1 and ISO 2768-2. ISO 2768-1 specifies general tolerances for linear and angular dimensions without individual tolerance indications in four tolerance classes: f (fine), m (medium), c (coarse), and v (very coarse). ISO 2768-2 specifies general geometrical tolerances for features without individual tolerance indications in three tolerance classes: H, K, and L.
The purpose of ISO 2768m is to simplify the drawing indications and reduce the number of tolerances required. It applies to the dimensions of parts that are produced by metal removal or parts that are formed with sheet metal fabrication. It does not apply to dimensions that have individual tolerance indications, auxiliary dimensions, or theoretically exact dimensions.
What are the tolerance classes and ranges?
The tolerance classes and ranges depend on the type of dimension and the nominal length. The tables below show the permissible deviations for linear dimensions, external radii and chamfer heights, and angular dimensions according to ISO 2768-1. The tables are based on the web search results .
Tolerance Class | Designation (Description) | f (fine) | m (medium) | c (coarse) | v (very coarse) |
---|---|---|---|---|---|
Linear Dimensions | 0.5 up to 3 | ±0.05 | ±0.1 | ±0.2 | — |
over 3 up to 6 | ±0.05 | ±0.1 | ±0.3 | ±0.5 | |
over 6 up to 30 | ±0.1 | ±0.2 | ±0.5 | ±1.0 | |
over 30 up to 120 | ±0.15 | ±0.3 | ±0.8 | ±1.5 | |
over 120 up to 400 | ±0.2 | ±0.5 | ±1.2 | ±2.5 | |
over 400 up to 1000 | ±0.3 | ±0.8 | ±2.0 | ±4.0 | |
over 1000 up to 2000 | ±0.5 | ±1.2 | ±3.0 | ±6.0 | |