The Extent of Location and the Choice of Location System

 The Extent of Location and the Choice of Location System

The location system used for a particular operation will depend upon the operation to be performed and upon the shape of the work piece before that operation. illustrates three stages in the machining of a part; when stage l is completed the part is symmetrical about the x-x axis, and so it does not need to be positioned about that axis when drilling hole A at stage 2. It must, however, be positioned so that the axis of hole A will be parallel to the X-X axis. When hole A has been produced the part is no longer symmetrical about the x-x axis and so it must be completely constrained before slot B is machined at stage 3.

Three stages in the machining of a part

Three stages in the machining of a part When there is a choice of location points the most effective location system must be selected; the choice will depend upon such features as simplicity of the system, accuracy of the location, ease of location and effect of wear upon the accuracy of the system. When a cylindrical hole or shaft is available as a location point it should be used if possible because cylindrical location eliminates all the freedoms except that of rotation about that of the cylinder.shows two methods of machining a part. After operation 1 has been completed that part is symmetrical about the axis of the bore. At this point there is a choice of method; either hole L or hole H can be machined at operation 2. In order to compare these two alternatives it is necessary to consider the location for operation 3.

When method A is used the part can be positioned for operation 3 by locating it from the bore and from hole L and when method B is used it can be positioned by locating it from the bore and hole H. Method A is the better method because the locators will be parallel and easy to see during location; method B is not a good method because the two locators will not be parallel, and so the locator that positions the part about the axis of its bore must be retractable and will wear during use; in addition to this objection, location will be awkward because the operator will not be able to see the location in hole H being done.

Two methods of machining a part (Location shown in heavy lines)