Geometrical elements of precision parts

Regardless of the structural characteristics of the parts processed by precision parts, the resulting body is composed of several points, lines, surfaces, and points. These points, lines, and surfaces are collectively called the geometric elements of the part.

Geometrical elements of the part

According to the role of elements in the body, there are some names.

1. Ideal and practical factors:

(1) Ideal elements are absolutely correct elements with geometric meaning, such as points, straight lines, planes, spheres, etc. It is in an ideal state without any shape error.

(2) The actual element is an element formed by machining that actually exists on the workpiece for processing precision parts. It is usually replaced by measured elements. Due to processing and measurement errors, the actual shape and position of points, lines, and surfaces cannot have ideal shapes and positions.

2. The measured element and the benchmark element:

(1) The measured element is the element that gives shape and position tolerance on the drawing, and it is the object of detection: the surface pointed by the guide arrow in the figure below.

(2) The reference element is the element used to determine the direction and position of the measured element should be marked with a reference symbol: as shown below, plane A is the reference element.

3. Single element and related elements:

(1) A single element is an element that requires shape tolerance only for the element itself. Elements that have only shape tolerance requirements but no position tolerance requirements on the drawing belong to a single element.

(2) Related elements are elements that have a functional relationship between the measured element and other elements. Elements that are required for position tolerance on the drawings of precision part processing drawings are related elements. Functional relationship refers to the orientation relationship between elements, such as vertical, parallel, coaxial, and symmetrical.