Making a pattern from a worn or broken casting without the aid of a blueprint happens from time to time. In scribing this layout, you must first obtain (by checking the casting) the centerlines or basic construction lines which will form the basis of the layout. The centerlines may be found very accurately by placing the sample casting on a surface plate. You then measure them from the surface plate to the center of the bosses, outlets, or holes by means of standard rules, squares, gages, or calipers. It is always best to work from a casting's machined surface if one is available. After the centerlines have been established by this method, you proceed to scribe the outline of the casting and to add the necessary details. Rememember that the proper shrink rule must be used when transferring the standard rule measurements from the casting to the layout.
The following procedure is presented as a guide for drawing a layout from a casting:
1. First, find out from what part of the major assembly the worn casting was removed. Be sure you understand the purpose and function of the assembly.
2. Inspect the part and the rest of the unit closely to identify the surfaces which require machining. In some cases it may be necessary to build up or restore the dimensions of the warn surfaces.
3. Apply the standard metal tests such as the spark, chip, or file tests, in order to identify the kind of metal used in the warn part.
4. Make a working sketch of the casting by transferring all measurements from the worn part, using the standard measuring instruments such as calipers, scale, trammel, dividers, etc.
5. From the sketch make a layout, using the proper shrink rule.
6. Locate the core prints and add the proper machine finish allowance.
7. Doublecheck the layout carefully against the sample casting before proceeding with the construction of the pattern.
Layouts From Worn Castings