The Gang-Graver Graduator: Mark Every Inch at Once, One Fraction at a Time

"The nature of my invention consists in providing (for the common two foot square) twenty-four gravers set in stocks each about twenty inches long, which are confined to the bottom of a carriage, fitted to move back and forth far enough to make the longest crosswise mark on the square, the carriage being pressed forward by the action of a cam, in the rear, which is brought to bear on the teeth of a movable scale, having the length of the marks for the different divisions arranged on it—and the gravers being set one inch apart from center to center" "The advantages thus derived are facility, uniformity, certainty, and perfection of the work, having the edge of the square smooth and free from all fractures, to which, in the usual method they are constantly liable."

**Bed and fence.** Screw a straight hardwood fence along a 45 cm hardwood board. Cut a 30 cm length of aluminium flat bar as the rule to be graduated, and make a hardwood slide it clamps to, running against the fence. **Screw feed.** Fix a nut to the bed's end and run an M6 threaded rod through it against the slide's end, with a knob and a disc marked in ten parts on its outer end. One turn moves the slide 1 mm, as Whipple's scroll cam moved his anvil one fraction per revolution. **Gang of scribers.** Drill a hardwood bar at 25 mm centres for twelve hardened steel scribing points, set them at the same height with a straightedge, and hinge the bar over the rule so it swings down across it. Fix stops on the bar's swing that limit its sideways travel to a short, a middle and a long mark, as Whipple's scale set the mark lengths. **Graduate.** For each of 25 turns of the screw, lower the bar and draw it across: short marks each millimetre, middle ones each 5 mm, long ones each 10 mm. Check the finished rule against a steel rule at every 25 mm and at its ends.

**Heman Whipple** of Shaftsbury, Bennington County, Vermont, received US 16,857, dated 17 March 1857. His machine had gage rubbers near the gravers' points to regulate the depth, levers and springs pressing the gravers down, a crank whose throw set the fraction, and a latch that stopped the machine when the divisions were done; he did not claim cams for moving gravers as such. His claims cover the scale index, the rack and pawl arrangement, the gravers in the carriage, the scroll cam, anvil and latch, and the mortise bolt that sets each graver. **Honest limits.** A hand jig with twelve scribers, an M6 screw and a millimetre rule stands in for his powered machine with twenty-four gravers and eighths of an inch. The notebook's step and spacing errors are examples. Your checked rule is the result.