Backenschmiege - Back Bevel

Reading thru the book Handbuch der Schiftungen by Manfred Euchner , I came across this method to  find the jack rafter side cut angle  in plan view. It's one of those drawings where you say, well of course of it works. Just never seen it drawn this way. It would also give you the roof sheathing angle.

German PDF file with back bevel saw blade angle (Maschinen winkel)

Schiftungen.

The consideration of the chapter .. Dachau averaging "given the numerous samples of composite roofs teaches us that the latter BEZW are formed almost exclusively by the intersection of gable roofs. Can be broken down into those. A simple gable roof, including understanding the shape of the roof, in which only two inclined to each other, intersecting planes form the roof in a straight line, like a lying, triangular prism, namely a right prism if the building floor plan rectangular, a truncated prism when it is trapezoidal in shape., the forming the bases of the prisms vertical levels, the gable of the roof or the building. become but the latter is replaced by planes which are inclined like the surfaces of gable roof to the horizontal plan level, ie with the latter an acute angle, so that the roof appears as a gable-less and in all drops out, the hipped, and the triangular faces, in which now the previously limited by vertical planes prism formed cut is glad Walme when the horizontal lying sides of the same with those of the saddle roof surfaces lying in a horizontal plane Krüppelwalme when the said sides in different horizontal planes.

The lines in which the saddle roof surfaces intersect Walmflächen glad ridges, and the intersection with the ridge of the roof is called attack point.In the horizontal projection of the ridges bisect the angle of the building plan, if the roof pitch on all sides assumed to be equal, and therefore we obtain for roofs with the same roof pitch the projections of the ridges and at the same time the attack points by bisecting the angle of the floor plan.The position of the points is not attack without affecting the distribution of the binder of the saddle roof. Of the main bundles of the same one is usually two on the same so that it faces with their the Walme, vertical sides are under this points found on this page, the hip rafters and indirectly the remaining timbers that form the hipped, a prop. The hip rafters are such that the amount drawn on the upper bounding surface of Gratsparrens center line with the ridge line, of which we have the projection in Gruudriss, coincide, ie that, conversely, a to outline level in the projection of the ridge built vertical plane of the hip rafter length of halved. Those parts of the roof areas, for which the ridges form the upper boundary formed by rafters, probably as the other rafters of the gable roof begin at the foot of the same (at the eaves), but not reach up to the ridge, but are au blunt the hip rafters Creating, they are all of different lengths and hot as distinguished from the rafters of the gable roof Schiftsparren or shifter. Similar considerations can also hire for such parts of roof surfaces for forming the timber rafters which. Absorbed from the ridge to a Throat rich (Kehlschifter), which is known to arise if the building floor plan has a re-entrant angle. The spatial valley line as well as the ridge line forming the median line of the upper surface of a bar, which is called a collar beam.