Transmission chain hanging error will affect the correctness of tool movement, in some cases, it is the main factor affecting the machining precision. For example, when the gear hobbing, hob speed and workpiece to speed ratio is constant, maintain strict movement relationship.

When the driving element drive in the chain (such as hobbing hanging wheel indexing worm gear, etc.) have the manufacturing error and assembly error, and in the use of the process of wear, will destroy the movement relations correctly, make out of gear errors (such as pitch error, cumulative pitch error and tooth profile error). Therefore, the transmission accuracy of machine transmission chain, first of all depends on the transmission component manufacturing and assembly precision, and the second transmission element related position in suspension in the chain.