机电专业英语 教学课件 作者 杨寿智 刘水平 机电专业英语.Lesson 7.pptVIP

Lesson 7 Work-Holding Methods and Standard Setups Text Before any machining can be done on the horizontal mill, the workpiece or work-holding fixture must be secured and aligned on the machine table. A specific setup will depend on the particular workpiece and the machining task to be done. Considerable ingenuity on your part is required to make a safe and secure setup that will not distort or damage the workpiece. Milling machine setups are almost infinite in number and it would not be possible to discuss them all. The purpose of this unit is to introduce you to the equipment and techniques for common setups on this machine. Direct Mounting to the Table A large variety of milling clamps are available for direct table mounting of the workpiece. Always follow the rules of good clamping. Clamping studs or bolts should be fully screwed into their T-nuts. Clamp nuts should have full thread engagement on studs. Studs or clamp bolts should be located as close to the workpiece as possible and clamp support blocks arranged so that clamping pressure is applied to the workpiece (Figure7.1). Clamps should be located on both sides of the workpiece if possible. This will ensure maximum safety.(Figure7.2). Clamp supports must be the same height as the workpiece. Never use clamp supports that are lower than the workpiece. Adjustable step blocks are extremely useful for this as the height of the clamp bar may be adjusted to ensure maximum clamping pressure. To protect a soft or finished surface from damage by clamping pressure, place a shim between the clamp and work (Figure7.3). If you are machining a rough casting or weldment (Figure 7.4), protect the machine table from damage by using parallels or a shim under the workpiece. Paper, plywood, and sheet metal are shim materials. Their selection depends on the accuracy of the machine cuts. Workpieces can be easily distorted, broken, or otherwise damaged by excessive or improper clamping. One solution to this problem is to use a scr