As the name indicates, the planer is used for finishing flat surfaces. In the ordinary planer, the work is moved, and the tool is at rest. A common form of this tool is shown in Fig. 183. It consists of a bed A, upon the upper surface of which suitable guides or ways are planed. The platen B is made to travel back and forth upon these ways. The platen has a rack on its under surface, into which the gear C meshes. This gear is driven by a train of gears from the shaft carrying the pulley D. The tool is carried on the tool-head E, where it can be given a slight vertical motion or feed. This tool-head may be fed across the machine by the screw in the cross-rail F. The latter may be raised and lowered by the shaft and gearing shown at the top. This gearing turns two vertical screws running in nuts attached to the cross-rail.
The reciprocating motion of the planer table is obtained as follows: The pulleys D and G run loose on the shaft, and are driven in opposite directions by belts from an overhead countershaft. The center pulley is fixed to the shaft, and either belt may be moved over on this pulley by the belt-shifters J, which are moved in opposite directions by a connection with the shifting lever 7, connected with them by suitable mechanism inside the bed, and acted upon by the reversing dogs H H, which are adapted to be adjusted at any point in the length of the table, according to the position of the work and the length of the stroke desired.
The planer shown in Fig. 183 has but one head for holding a tool. In large planers it is customary to have two heads on the cross-rail, so that two tools may be cutting simultaneously, thus doubling the capacity of the machine. The vertical feed of the tool is also operated automatically; and in a planer having two heads, both vertical and lateral feeds are independent of each other.
Fig. 133. Common Type of Planer.
Fig. 184 shows a large planer equipped with two heads on the cross-rail, and a still further equipment of two heads with automatic vertical feeds on the side posts. Thus arranged, the machine is capable of handling very large work, and of keeping four tools cutting simultaneously. The table-operating mechanism within the bed is substantially the same in nearly all except some special planers. In this planer, there is a driving belt on each side of the machine, one running the table forward, and the other backward, the rod carrying the belt-shifters passing entirely through the machine.
Fig. 184. Large Planer with Two Heads on Cross-Rail and Two Heads on Side Posts Courtesy of Cincinnati Planer Company, Cincinnati, Ohio.
The speed of travel forward of the table is the ordinary cutting speed; while, to save time, the return or backward movement is as fast as the driving mechanism will permit. The ratio of forward to backward speeds will be from 2 to 1 (in very large planers), to 4 to 1 (in small planers).
Ordinarily the tool cuts only when the platen is moving toward the right, Fig. 183. As a result of this condition, the platen is made to move more rapidly toward the left than toward the right. This is accomplished by varying the speeds of the pulleys D and G. The usual ratio of the speeds of these pulleys is 2 to 1 or 3 to 1.
The feed of the tool is accomplished by a friction clutch driving the vertical rack K. This acts only at a point near the end of the travel of the platen. It is so arranged that any reasonable vertical or horizontal feed may be given to the tool.
The machine is driven by three driving pulleys placed side by side on the same shaft, the central one of the three being keyed to the shaft. The reversal of the motion of the platen is obtained by shifting one or the other of the belts onto the central pulley.