The Rafter Layout Instrument: One Length, Two Bevels, Every Rafter Alike

"In making my invention, construct the measure (A—B) of wood having the extremities plated with brass; make it in two parts with clasps (C) so arranged as to connect the two parts together and at the same time allow them to be drawn or extended lengthwise by each part sliding through the clasp of the other part." "Each end of the measure is provided with a bevel (D—E) working upon a pivot (H)."

**Measure.** Saw two strips 60 × 2.5 × 1 cm from hardwood board. Bend two strips of aluminium sheet round both strips into clasps and rivet one to the end of each strip, so each slides through the other's clasp. Mark centimetres along both with the ruler and pencil. **Bevels.** Cut two blades 15 × 3 cm from plywood and bolt one to each end with a hex bolt and nut, tight enough to stay where set. Draw a half-circle protractor on card at each pivot and glue it on. **Test.** Lay out a 1:10 model of a 6 m span at 35°: set the measure to the notebook's rafter length divided by ten, set the top bevel to 35° and the bottom to 55°, and mark four rafters on a pine board. Saw them, stand pairs on a base 60 cm wide and check they meet at the ridge and sit flat. Mark two more with a loose bevel gauge and ruler and compare the fit.

**LeGrand Crofoot** of Syracuse, New York, received US 15,600, dated 26 August 1856, for an instrument for laying out rafters. His bevels were held by set screws on graduated arcs whose divisions could be read as roof pitch or as degrees, fixed square plates at each end marked the side surfaces, and sliding square plates marked tenons on the ends of timbers. **Honest limits.** Wooden strips, riveted clasps and bolted plywood blades stand in for his brass-tipped measure and set-screw bevels, and the model is at 1:10. The notebook ignores overhang and the ridge board's thickness; its spans and pitches are examples. Your model's fit is the result.