The work of the machinist is to shape metal to a definite form, size, and finish by the use of grinding and cutting tools, and to assemble, repair, and erect machines. The metal in its original form may be a casting, a forging, or a piece of stock of indefinite form from which the required object is to be shaped. Designing the part often tests the ingenuity of the machinist, as he must devise ways and means to perform the various operations so that the dimensions when finished will be accurate and will correspond to those given on the blue-print. Before a machinist begins to grind or cut a casting he marks out the outlines, holes, and machine cuts required. This is called laying-off work; the measurements are carried out by means of a center punch and dividers. The casting is then attached to the plate or table of the machine tool by means of special bolts and plates. When a great many castings of the same kind are to be machined special devices, called jigs, are employed to hold them. A jig is a great aid to quick work.
The casting is shaped by cutting or grinding the excess metal by means of various power tools. Chips may be removed also by means of a hammer and chisel. The surface is smoothed by filing. Benchwork or visework consists in fitting and finishing the machine, and floorwork in assembling the parts. Considerable skill is often required to file and scrape the parts true, so that they fit perfectly when the machine is finally assembled.