The Sash Fastener: Two Cams on One Shaft Squeeze the Window Shut

"My invention relates to that class of sash-fasteners in which a cam is employed to compress the sash to be locked or fastened". It consists "in the employment, for the purpose mentioned, of a double cam or eccentric, or two cams, or eccentrics, mounted upon the same shaft, arranged in such manner that the movement of the fastening-device or devices, by which the sash is compressed, shall be equal to the sum of the eccentricities of the two cams." "The fastener is composed of two plates, A B, placed one upon the other." The two eccentrics "are so placed that the point of greatest departure from the axis of the shaft in the one will be diametrically opposite, or thereabouts, the like point of the other." "These two plates may be let into the side of the window-frame contiguous to the sash or sashes, so that the exterior plate B will be flush with the face of the jamb. They can be used with either one or two sashes, and to compress either or both."

Cut two plywood strips 120 x 30 mm to be the plates, and two discs 30 mm across to be the cams. Drill each disc 3 mm off its centre and glue them together on one bolt with their offsets opposite. Cut a round-ended slot in the top strip a little wider than a disc, and one in the bottom strip for the other disc; in the bottom strip also cut a slot for the bolt, as long as the cam's throw, so the shaft itself can move. Put a lever on the bolt head. Turn the lever and measure the top strip's travel with a caliper, first with the bottom strip clamped still and then with it free. Compare with one throw and with the sum of both. Then look at a sash lock on a real window: find its cam, and where the turn stops pushing and starts squeezing.

**Walter K. Marvin** of New York received US 83,983, dated 10 November 1868 (no filing date is printed on patents of that period). He notes it can fasten "the single sashes of railway-car windows" too. **Honest limits.** The patent gives no sizes. The throws, crank length and handle force in the notebook are examples, and the squeeze figure ignores friction, which is what actually lets the cam hold.