The Design of Cam-linkage Self-centering Steady Rests

• Main Authors: Wei, sung, 魏嵩
• Other Authors: Wu, long iong
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/93329599251327064972

碩士 === 國立清華大學 === 動力機械工程學系 === 102 === The steady rest is a gripping device to support a long cylindrical workpiece and is often used when a slender shaft is machined on the lathe. Furthermore, the self—centering steady rest can help the cutting cylindrical workpiece to additionally keep a stationary center. The cam-linkage type self-centering steady rest is the most popular one, but how to design such a device has not been illustrated. The purpose of this thesis is to present a method for designing the cam-linkage self-centering steady rest. The cam-linkage self-centering steady rest can be either the active translating cam type or the active translating roller link type, and both of them have three grippers. In order to keep the cutting workpiece having a stationary center, the relative positions and the instant centers of three grippers must be a function of the workpiece radius. Either the contact points between the cam and the followers or the contact points between the active roller links and the inverse cam can then be determined according to the locations of instant centers. Consequently, the cam profiles, their radii of curvature, and the pressure angles can be expressed in the form of parametric equations. In addition, for their proper operation, some geometric constraints of each link of the self-centering steady rest must be observed and can be calculated. After a force analysis of the steady rest has been undertaken, the forces applied on each gripper can be determines, and the contact stress among the workpiece and three gripping rollers can be calculated. By applying the equivalent linkage method, finally, the radius varaion as well as the eccentric amount of the cutting workpiece caused by each link length deviation can be estimated. The designer may accordingly assign proper tolerances on each member of the steady rest to restrict the output within a specified maximum value.