Most of the blanks used for shaft parts are profiles (steel), which are round, square, hexagonal and other special shapes. According to its accuracy, it can be divided into: 1) ordinary precision hot rolled material and 2) high precision cold drawn material. Common mechanical parts are mostly hot-rolled  . When the outer circle can not be machined, the cold drawn profile can be used.

II. Machining allowance of blank

During machining, in order to ensure the machining quality, it is also the difference of dimensions before and after machining. The difference between part size and blank size is called blank allowance

The blank allowance of castings shall be determined by the foundry workshop personnel.

III. machining allowance between processes

The metal layer required to be reserved to ensure the quality of a process is called the process margin of the process. The size of process allowance has a great relationship with improving   part processing quality and labor productivity. We should pay attention to the following points when taking allowance in the process,

1. The advantage of selecting machining allowance is that it can shorten the machining time and reduce the production cost. Note: you can't change the size. In particular, for the following processes, generally speaking, the machining allowance shall ensure that the surface finish (roughness) and dimensional accuracy specified in the drawing can be guaranteed after machining.

2. When determining the machining surface allowance, the size of the part should be considered, because after the part size becomes larger, the possibility of deformation caused by cutting force and internal stress also increases. Therefore, the more the parts are, the larger the machining allowance is.

3. When determining the machining allowance, it is also necessary to consider whether the parts are treated and the deformation of hot spots.

4. Pay attention to the equipment and processing methods used