SECTION 6.2

1. The design or selection of a workholder is governed by many factors, the first being the physical characteristics of the workpiece. The workholder must be strong enough to support the workpiece without deflection. The workholder material must be carefully selected with the workpiece in mind so that neither will be damaged by abrupt contact.
   Cutting forces imposed by the broaching operation vary somewhat in magnitude and direction. However, it usually causes a straight line thrust. The workholder must support the workpiece in opposition to the cutting forces and will generally be designed for each specific application.
   
   
2. The workholder must also establish the location of the workpiece relative to the broach tool. If the operation is to be performed at a precise location on the workpiece, locating between the workpiece and workholder must be equally precise. If the broach tool must engage the workpiece at a specified distance from a workpiece feature such as a line or plane of the workpiece, then the workholder or workholding fixture must establish the line or plane at the specified distance. The degree of precision in the workholder will usually exceed that of the workpiece because of cumulative error.
   
   
3. The strength and stiffness of the workpiece will determine to what extent it must be supported for the broaching operation. If the workpiece design is such that it could be distorted or deflected by machining forces, the workholder must support the affected area. If the workpiece is sufficiently rigid to withstand the machining forces, workholder support at the edge of the workpiece may be adequate. The strength of the workholder is determined by the magnitude of the machining forces and the weight of the workpiece.
   
   
4. Safety requirements must always dictate workholder design or selection. A workholder must not only withstand normal cutting forces and the workpiece weight but may also have to withstand large momentary loads. In machining a cast workpiece, the broach tool might strike an oxide inclusion causing instantaneous multiplication of force. The tool might cut through the inclusion, the tool might break, or the machine might stall. If the workholder broke, however, the tool might impart motion to the workpiece. A workpiece in uncontrolled motion is a missile. The workholder must also be designed to protect workers from their own negligence. Where possible, a shield should be interposed between the worker and the tool.
   
   
5. A workholder should be designed to receive the workpiece in only one position. If a symmetric workpiece can be clamped in more than one position, it is probable that a percentage of workpieces will be incorrectly clamped and machined. Workholders should be designed to prevent incorrect placement and clamping.
   
   
6. It is advisable to use standard workholders and commercially available components whenever possible. Not only can these items be purchased for less than the cost of making them, but they are generally stronger and more accurate.