1. Base material: the base material shall be correctly selected according to its structure, process, cost, production batch and production cycle, Common are: (1) Cast iron: it is easy to cast into parts with complex shape; The price is cheaper; Cast iron has large internal friction and good vibration resistance. his The disadvantages are long production cycle and high single piece production cost; Castings are easy to produce waste products and the quality is not easy to control; Machining allowance of castings Large, high machining costs. There are two kinds of commonly used gray cast iron: HT200 is suitable for those with simple shape and large unit pressure (P > 5kg / cm2) Guide rail, or one with large bending stress（ σ 2300kg / cm2) bed, etc; HT150 has good fluidity but mechanical property It is suitable for the base with complex shape and small load. If gray cast iron cannot meet the wear resistance requirements, wear resistance shall be adopted Cast iron. (2) Steel: welded into a frame with steel. The elastic modulus of steel is larger than that of cast iron, the wall thickness of welded frame is thinner, and its weight ratio is the same The rigidity of the base is about 20% ~ 50% lighter; In the case of single piece small batch production, the production cycle is short and the required equipment is simple; weld The disadvantage of the connecting frame is that the anti vibration performance of steel is poor, and anti vibration measures need to be taken in the structure; Large workload of fitter; mass production The cost is high.