For refined base consideration will focus on how to reduce errors, improve positioning accuracy, so choose refined base principles are:
First, the benchmark coincide principles: the design basis should be used wherever possible as positioning reference. Especially in the final finishing, to ensure accuracy, but also should pay attention to this principle. This avoids positioning errors due to baseline caused no coincidence;
Second, the principle of unity of reference: the surfaces should be used wherever possible unified positioning reference processing, in order to ensure the accuracy of each position between the surface; principle sometimes follow each other benchmarks, repeated processing;
Third, since the basis of the principle: Some finishing operations require small and uniform allowance, in order to ensure processing quality and increase productivity, then you to the machined surface itself as a fine base.