Double or binary planing, is that in which two planing-tools of one machine cut at one time, either while producing planes on two different objects, or while producing two planes on one object. This species of planing is denoted in Fig. 767, in which two pieces are seen fixed to two el-chucks, in order to plane both articles at one time on one machine. Triple planing is that by which three tools of one machine cut at the same time instead of only two. There are also planing-machines capable of producing four, five, or six planes at once, on one machine, by means of two carriages, and slide-rests attached to the machine's standards; and, in accordance with the terms just given, such planing may be named, quadruple, quintuple, sextuple, etc.

This chapter is now closed, by mentioning that a variety of curved surfaces also are produced with planing-machines in addition to the production of ordinary planes. The shaping of curved surfaces by planing-machines, has been partly treated in this chapter, because the shaping of curves cannot be quite distinctly treated, through some objects being both plane and curved. Planing, is a general term for work effected on a planing-machine, whatever may be the shapes of the surfaces which are formed ; and it will be observed that planing constitutes a necessary portion of the next chapter, which is devoted to shaping in general.