The Clamp Skate: One Screw Closes the Toe and Heel Jaws

"The object of the present invention is to facilitate the adjustment of the toe and heel-jaws by so setting the adjusting-screw that it can be easily reached by the wearer." "In the skate described in the aforesaid Letters Patent, the screw was set longitudinally, and was therefore difficult to reach". "This longitudinal adjustment is obtained by means of a right and left screw, G, which is fitted through nuts g h, that are respectively pivoted to the inner ends of the levers E F, so that they can freely turn on their pivots. As by turning the screw G the nuts are forced further apart, the clamp-levers are moved outward, to spread the jaws, while the latter will be contracted when the nuts are drawn together." On the heel-plate is "an upward-projecting lug, i, with a backward-projecting prong or point, j, which serves to retain the heel and boot in position, longitudinally as well as vertically."

Take an adjustable clamp-on skate. Measure the gap between the toe jaws with a caliper, turn the key one full turn and measure again; repeat for five turns. Compare the change per turn with twice the pitch times the lever ratio. Clamp it onto a hard-soled shoe held in a vise by the upper, tightening the key the same way each time. Hook a spring scale to the skate's runner and pull sideways until it slips on the sole. Try half a turn tighter and looser. Never skate in a clamp that slips under a hand pull.

**Charles T. Day** of Newark, New Jersey, received US 98,237, dated 28 December 1869 (no filing date is printed on patents of that period); it improves his US 40,916 of 15 December 1863. **Honest limits.** The patent gives no pitch or lever lengths. The pitch, efficiency, lever arms, friction coefficient and torques in the notebook are examples.