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用导套引导的齿条式拉刀拉键槽时,键槽的底面往往不能与孔中心线平行——拉刀出口处的尺寸大于入口处的尺寸(如图1 t_1>t_2)。用不同长度的两个导套拉削图1所示的工件时,偏差情况如右表。可见用长导套要比用短导套拉出的键槽精确得多。原因是,导套的长度不足时,切削力P(如图2)不能通过导套与拉刀的接触基准面,在P力弯曲力矩的作用下拉刀杆产生变
When using a guide sleeve with a guide bar, the underside of the keyway can not be parallel to the centerline of the hole - the size of the broach outlet is larger than the size of the entrance (see Figure 1 t_1> t_2). When using two guide bushings of different lengths to pull the workpiece shown in Fig. 1, the deviation is shown in the right table. Visible with a long guide sleeve than with a short guide sleeve pulled out of the keyway is much more accurate. The reason is that when the length of the guide sleeve is not enough, the cutting force P (as shown in FIG. 2) can not pass through the contact plane between the guide sleeve and the broach and the bar will be deformed under the bending moment of P force