学习啦【英语散文】 编辑：韦彦 发布时间：2016-09-14
Angle milling cutter. An angle milling cutter is employed in cutting dovetail grooves, ratchetwheels, and the like. Fig.12.4e indicates a milling cutter of this type.
T-slot cutter. As shown in Fig.12.4f, a T-slot cutter involves a plain milling cutter with anintegral shaft normal to it. As the name suggests, this type is used for milling T-slots.
End mill cutter. End mill cutters find common applications in cutting slots, grooves, flutes,splines, pocketing work, and the like. Fig.12.4g indicates an end mill cutter. The latter is alwaysmounted on a vertical milling machine and can have two or four flutes, which may be eitherstraight or helical.
Form milling cutter. The teeth of a form milling cutter have a certain shape, which is identicalto the section of the metal to be removed during the milling operation. Examples of this typeinclude gear cutters, gear hobs, convex and concave cutters, and the like. From millingcutters are mounted on horizontal milling machines.
Materials of Milling Cutters.The commonly used milling cutters are made of high-speed steel,which is generally adequate for most jobs.
Milling cutters tipped with sintered carbides or cast nonferrous alloys as cutting teeth areusually employed for mass production, where heavier cuts and/or high cutting speeds arerequired.
Although small tolerances give higher quality work and a better operating mechanism, the cost of manufacture increases rapidly as the tolerances are reduced, as indicated by the typical curve of Fig14.1. It is therefore important that the tolerances be specified at the largest values that the operating or functional considerations permit.
Tolerances may be either unilateral or bilateral. In unilateral dimensioning, one tolerance is zero, and all the variations are given by the other tolerance. In bilateral dimensioning, a mean dimension is used which extends to the midpoint of the tolerance zone with equal plus and minus variations extending each way from this dimension.
The development of production processes for large-volume manufacture at low cost has been largely dependent upon interchangeability of component parts. Thus the designer must determine both the proper tolerances for the individual parts, and the correct amount of clearance or interference to permit assembly with the mating parts.
The manner of placing tolerances on drawings depends somewhat on the kind of product or type of manufacturing process. If the tolerance on a dimension is not specifically stated, the drawing should contain a blanket note which gives the value of the tolerance for such dimensions.
However, some companies do not use blanket notes on the supposition that if each dimension is considered individually, wider tolerances than those called for in the note could probably be specified. In any event it is very important that a drawing be free from ambiguities and be subject only to a single interpretation.