Manufacturing Knowledge Base

This chapter has been adapted from SME’s Fundamentals of Tool Design, Fifth Edition (2003). The term work holder includes all devices that hold, grip, or chuck a work piece to perform a machining operation. The holding force may be applied mechanically, electrically, hydraulically, or pneumatically. A work holder must position or locate a work piece in definite relation to the cutting tool, and it must withstand holding and cutting forces while maintaining a precise location. Work holders also may be used for assembly, welding, and inspection operations. Work holders are commonly classified as fixtures or jigs. Fixtures are work holders designed to hold, locate, and support the work piece during a machining cycle, joining, or assembly operation. Fixtures do not guide the cutting tool, but rather provide a means to reference and align the cutting tool to the work piece. Jigs, like fixtures, hold, locate, and support the work piece, but also guide the cutting tool throughout its cutting cycle. Drill jigs are the most common type of jig. They are used for drilling, tapping, reaming, countersinking, counter-boring, chamfering, and spot-facing.