Basic Principles For Dimensioning Of Mechanical Parts

DALIAN, China - Jan. 1, 2023 - PRLog -- Reasonable Selection Of Dimension Datum:

The starting point of dimension is called dimension datum (abbreviated as datum). Generally, the face (such as end face, bottom face, symmetry plane, etc.), line (such as axis), and point on the part are selected as the datum. There are two kinds of dimension datum on parts, namely design datum and process datum.

From the design point of view, some benchmarks selected to meet the specific requirements for the structure and performance of parts in machines or components are called design benchmarks. The design basis determines the location of parts on a machine or assembly.

From the perspective of processing technology, some benchmarks selected to facilitate the processing, measurement and assembly of parts are called process benchmarks.

In order to reduce the size error and ensure the product quality, it is better to unify the design datum and process datum when dimensioning. If it cannot be unified, the main dimensions shall be marked from the design basis.

Dimensioning Principles Of Common Parts:

Shaft Sleeve Parts:

Generally, the axis is selected as the radial dimension datum (the axis is both the design datum and the process datum), and the important shoulder surface or end face (the locating surface or the contact surface) is used as the dimension datum in the length direction. The main dimensions with design requirements must be marked directly from the datum, and the other dimensions are generally marked according to the processing sequence. The dimensions of standard structures (such as chamfer, undercut, keyway, etc.) shall be marked after referring to relevant manuals.

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