First, the interchangeability of parts

Precision parts processing manufacturers introduce that after long-term production and operation of the machine, some parts will inevitably wear out, deform and be scrapped, and replaced with new parts. These parts are called accessories or spare parts. Accessories or spare parts can be installed on the machine without repair or selection, which is called interchangeability.

In order to achieve interchangeability, when manufacturing parts, the size, geometry, etc. of the parts should be made consistent. The so-called consistency is not required to be exactly the same (it is neither economical nor possible to do so), as long as the size and geometry of the parts are controlled within an allowable range, so that the parts and other parts have the same bonding performance. This allowable error range is the shape and position tolerance.

Second, the machining quality of precision parts is expressed by machining accuracy.

1. Geometric shape accuracy

Geometric shape accuracy refers to the accuracy of the geometric shapes such as the surfaces or axes of the components, such as whether the lines are straight, whether the surfaces are flat, and whether the regular sections on the cylinder are round. The allowable range of variation is expressed as "shape tolerance". The smaller the number of shape tolerance, the higher the shape accuracy.

2. Dimensional accuracy

Precision parts processing manufacturers analyze that dimensional accuracy refers to the accuracy of the size of the part after processing, expressed as "dimensional tolerance". When the size of the parts is the same, the higher the accuracy, the smaller the tolerance number.

3. Position accuracy

Precision parts processing manufacturers introduce that positional accuracy refers to the accuracy of the mutual positions between the surfaces of the components, such as whether the two planes are parallel, vertical, and whether the two axes are coaxial, etc., expressed as "positional tolerances".

The above shape and position tolerances are referred to as "shape and position tolerances".