Work is rarely laid out for the lathe. It is not necessary that it should always be done for the planer. Laying out is employed where accuracy is essential, and where it is possible to secure the proper dimensions, with the piece to be operated upon in position on the machine.
The man who has charge of the work of laying out should have some knowledge of the elementary principles of geometry; he should also have some knowledge of drawing, and should, of course, be able to read drawings.
A few general suggestions may be given regarding work to be finished in the vise on either the planer, shaper, or milling machine, where several faces are to be finished at right angles to one another. Referring to the rectangular block of Fig. 253, the block is first placed in the vise with the face MNOP down, and the face MADP against the fixed jaw. The face ABCD is then machined, and the work turned so that ABCD is against the fixed jaw, and MADP down, With the block in this position, NBCO is worked, making NBCO at right angles to ABCD. With ABCD still against the fixed jaw, and NBCO down, surface MADP is next worked. This brings two edges at right angles to the same side and parallel to each other. Then, placing ABCD down and either MADP or NBCO against the fixed jaw, surface MNOP is generated parallel to ABCD. This leaves the ends to be finished. The vise is swung so that the fixed jaw is at right angles to the line of motion of the tool; and on the planer and shaper they are finished by using the vertical feed. In the two last-named tools, the tool holder is swung so that the tool will clear the work easily on the return stroke. In working cast iron it is well to chamfer the edges with a file. If this is not done, the metal will break off when the tool reaches the end of the cut, leaving a ragged edge. The depth of the chamfer depends on the amount of metal to be removed.