Abstract: A motion model of tangential point tracing grinding has established according to the principle of grinding point’s uniform motion on the neck of connecting rod，and a new idea that changes the crank tangential point tracing grinding into the state of common external grinding is described through coordinate converting．According to the motion model，the influence of machining error caused by the tangential point tracing is analyzed．The influence and change rules of equivalent grinding thickness and grinding force of the tangential point tracing motion are discussed．The computer formula of NC compensation and the revised motion model are given．

Key words: Coordinate converting Equivalent grinding thickness, Crank, Machining error, Tangential point tracing grinding Motion model