Selection of the datum and determination of the precision of the spiral bevel gear

1) Selection of rough datum

According to the principle of selection:

(1) Principle of non machined surfaces.

(2) The principle of minimum machining allowance.

(3) Important surface principles.

(4) Principle of non reuse.

(5) The principle of easy clamping.

2) Selection of precise datum

The design basis is the basis adopted in the drawing. For example, the axis line on the part drawing is the design basis of each outer circle and hole. From the process analysis of the part, it can be seen that the design basis of the part is the axes of Φ 50k6mm and Φ 35mm, and the selection principle according to the precise basis is as follows:

(1) Principle of datum coincidence.

(2) The principle of datum unification.

(3) The principle of self reference.

(4) Principle of mutual benchmark.

(5) The principle of easy clamping.

According to the above selection principle, when processing: also from the product use aspect, the Journal of the active spiral bevel gear (Φ 65mm) and the Journal (Φ 50mm) are the mating surfaces, according to the installation distance (118mm), it can be seen that the journal end face of Φ 65mm is the assembly datum; from the product design aspect, the journal end face of Φ 65mm is the design datum, and its axis is the datum of the form and position tolerance. Therefore, it can be determined that the positioning datum of the tooth profile machining should be the end faces of the two journals (〝65mm and〝50mm) and the Journal (〝65mm).