An automatic power cutter is operated first by determining the line of the cut by the indicator or by pulling the clamp down upon the work; then pulling the starting lever, which automatically forces the clamp down first upon the stock, and then drives the knife through it, and returns both knife and clamp to stop at the top.
Automatic-clamp power cutting machines are also furnished with hand-clamp attachment for special clamping pressures.
Continuous running is effected by devices which permit the quick disengagement of the stop throw-out mechanism. This is desirable with duplicate work in quantities carefully arranged for fast production. Automatic cutting machines are also furnished with spacing devices for the rapid duplication of exact widths of any size.
Vertical stroke (and vertical changeable to shear stroke) cutting machines (see Fig. 9, page 17), both hand power and also power, are used with special shaped knives for cutting fancy edges, and pinking cloth samples, etc., some having back tables of great length, moved on rollers or slides by spacing devices. Considerable ingenuity has been shown in the variable method and mechanism used for moving the knife up and down.
The Knife
The knife is most important. It must be kept sharp. It must be of the proper shape and thickness and bevel and temper and free from any burrs or lumps on its back edge. A cutting-machine knife is like a razor that, stropped correctly, does not pull the beard, but stropped an infinitesimally different way—a difference impossible to see except with a microscope—pulls hard. Study carefully the knife. No matter how carefully the machine is built, an imperfect knife cannot cut right. Most knives are imperfect in spite of the rigorous specifications given them by makers. They vary in thickness, straightness, concave, bevel, flatness, temper, and quality of steel; and also in the character of their sharpening and honing, which varies with the fineness or coarseness of the grinding wheel and stone. These variations need only be a few thousandths of an inch to cause trouble.
Fig. 9
VERTICAL-STROKE POWER MACHINE
Changeable to Double Shear
A blue wave mark indicates where the temper is drawn, and a file which "drags" when pushed fairly hard across the flat of the bevel indicates the soft spots, where the temper is imperfect.