The planer is one of the heaviest of machine tools. Planing is rough and heavy work, and rigid construction and stiffness are needed to take the heavy cuts, as the surfaces of castings and heavy forg-ings are usually hard crusts difficult to remove. In most shops much of this rough cutting is saved by the use of a pickling solution of one part sulphuric acid to eight parts of water. This solution is painted over the casting, and after four or five hours washed off with clear water, thus removing the sand and hard grit from the surface. If the castings are small, they are put with the pickling solution into a wooden vat into which a small amount of steam is injected. The castings are thus easily prepared for machining.

For roughing cuts on a planer, a highly tempered diamond-nosed tool is used which must be kept sharp by grinding. The cut of the roughing tool should be deep enough to go below the scale or surface, and thus allow the tool point to reach soft metal. Care must be taken not to allow the tool to ride over the hard scale, without doing any work, as a heavy drag on the machine will thus be caused. In cases where the casting is out of level, it should be leveled as nearly as possible. In such cases several cuts will be necessary to get the planer properly started. Any hard burr or sand-hole lump on the surface of the casting is best removed by a chisel and hammer, as an unnecessary strain is thrown on the machine tools when an attempt is made to remove them by planing.

After the surface is smooth, the round-nosed tool may next be used to plane to size and to proper depth. Some work may require no further finish than this. In cases where a smoother finish is desired, a square or flat-nosed tool is fed with a rapid revolution of the feed screw, sometimes as much as one-fourth revolution per stroke of the planer platen. The cross-rail is supplied with two feeding devices on single-head planers, "cross" and "vertical." The tool-head is marked with graduations for any desired angle.

Care must be taken during the operation of a planer that chips and dirt from the platen are not swept or allowed to blow into the V-ways,as this will cause injury to the machine. Oil should also be freely supplied to the machinery under the planer platen; these parts are likely to be neglected because they are hidden.

The installation and erection of a planer is of much importance, as poor work will result from a machine built on a poor foundation. A planer 24 in. X 24 in. X 6 ft. will consume an average of .035 horse-power for every pound of cast iron removed per hour and .065 horse-power for every pound of machinery steel removed per hour. The ignorant operator may, by the way he grinds and sets his tools, waste much power in driving the machine.