The disk or cutter head is in one piece with the spindle, and carries twenty-four cutters arranged in a circle of 36 inches in diameter. These cutters are made from the square bar, and each cutting point should have the same form and position as referred to one face, side, or square of the bar, so that each cutter may take its proper share of the cutting duty; and it is obvious that all the cutting edges must project an equal distance from the face of the disk, in which case smooth work will be produced with a feed suitable for the whole twenty-four cutters, whereas if a tool cuts deeper than the others it will leave a groove at each passage across the work, unless the feed were sufficiently fine for that one tool, in which case the advantage of the number of tools is lost.
The cutters may be ground while in their places in the head by a suitable emery-wheel attachment, or if ground separately they must be very carefully set by a gauge applied to the face of the disk.
Chapter XVII.—PLANING MACHINERY.
[Fig. 1565] represents a planer by William Sellers and Co., of Philadelphia, Pennsylvania. This planer is provided with an automatic feed to the sliding head, both horizontally and vertically, and with mechanism which lifts the apron, and therefore the cutting tool, during the backward stroke of the work table, and thus prevents the abrasion of the tool edge that occurs when the tool is allowed to drag during the return stroke. The machine is also provided with a quick return motion, and in the larger sizes with other conveniences to be described hereafter.
Fig. 1565.
The platen or table is driven by a worm set at such an angle to the table rack as to enable the teeth of the rack to stand at a right angle to the table length, and as a result the line of thrust between the worm and the rack is parallel to the V-guideways, which prevents wear between the Vs of the table and of the bed.