The Screw-Set Carpenter's Square: A Hidden Clamp That Sets the Blade True

"To this end I employ a slotted piece of metal J, having a shoulder on its lower end, on which the lower edge of the tongue or blade A, rests—a piece being cut out of the blade to allow it to fit well down on the beveled shoulder of the piece J, and to keep the piece from slipping out of its place. This piece J, terminates at its upper end in a screw g, that projects above the head of the stock B, and into the T-slot as shown in Figs. 1 and 3, and receives a milled nut h, which presses on the head or end of the stock B, when screwed up, and draws upon the blade A." "It will thus be seen that to 'set' or fix the blade at an exact angle, after the pins have been inserted that secures it to the stock, it is only necessary to turn the nut h, when the blade may be drawn or forced to its proper position to a nicety, and it may afterwards be kept so."

**Stock.** Plane a hardwood stock 25 cm × 5 cm × 22 mm and saw a slit into one end, across its width, that the blade fits. Mortise a recess C inside the slit near the head and drill down from the head's end into it for an M5 screw. **Blade.** Cut a 35 cm blade from aluminium flat bar. Near the end that enters the stock, file a notch with a beveled lower edge. **Clamp J.** Cut a short strip of steel with a bent-over shoulder that fits the blade's notch, and silver-solder an M5 screw to its upper end as g. Put it in the recess so the screw passes up through the head, and fit a knurled or wing nut on it as h. **Pins.** Put the blade in the slit, drill one hole through stock and blade near the pivot end and fit a pin as c; fit a second, looser pin c′ nearer the head. **Set it true.** Draw a line along a straight board's edge with the square, flip it and draw again. Turn the nut until the two lines agree, and note how much it took.

**James Hathen** of Philadelphia, Pennsylvania, received US 28,859, dated 26 June 1860; Charles Disston was one of his witnesses. The stock B was wooden with the usual metal face plate a, the blade was inserted in a slit cut transversely into its end, and all the parts were within the stock except the thumb screw. His claim is one or more adjusting clamps J at either end of the stock, used with the pins c and c′. **Honest limits.** Aluminium flat bar and a soldered strip stand in for his steel blade and clamp, and the face plate is left out. The notebook treats the blade as turning about one pin; its pitch and lengths are examples. Your flip test is the result.