A machinist constructing a machine or machine part from drawings requires not only a true representation of the object to be built, but every one of its dimensions. The drawing must also give other instructions like the material being used, the method of manufacturing, etc. A mechanical drawing of this kind is called a working drawing.
Working drawings are divided into two general classes; namely, assembly, or general, drawings and detail drawings.
Assembly, or general, drawings give the workman the relation between, and the places or positions occupied by, the component parts of a structure, machine, device, fixture, implement, etc. If any dimensions are given they are the principal ones, such as distances between the center lines of the main parts of a machine or engine, etc.
Detail drawings show the exact shape and size of each individual, part and also the material. For this purpose they are supplied with all the dimensions required by the workman and any explanatory notes that the draftsman may consider necessary.
Detail drawings may be made so complete that they will answer for the pattern maker, shop smith, and machinist, and they’re usually made in the smaller shops. In the large shops, however, separate drawings are often made for these different professionals. The detail drawing for the use of the pattern maker usually has only the dimensions and notes needed by them to make the pattern. For the mold maker and shop smith, the drawings only contain the dimensions needed for making the forging. Finally, whats needed for the machinist will have only the dimensions that they need.