Page:Sheet Metal Drafting.djvu/216

202 {|
 * Triangles.
 * Altitudes.
 * Triangles.
 * Altitudes.
 * Triangles.
 * Altitudes.
 * A to 1|||1|||D to 4|||4|||G to 7||7
 * 1 to B|||1|||4 to E|||4|||7 to H||7
 * B to 2|||2|||E to 5|||5|||H to 8||8
 * 2 to C|||2|||5 to F|||5|||8 to J||8
 * C to 3|||3|||F to 6|||6|||J to 9||9
 * 3 to D|||3|||6 to G|||6|||9 to K||9
 * }
 * 2 to C|||2|||5 to F|||5|||8 to J||8
 * C to 3|||3|||F to 6|||6|||J to 9||9
 * 3 to D|||3|||6 to G|||6|||9 to K||9
 * }
 * 3 to D|||3|||6 to G|||6|||9 to K||9
 * }
 * }
 * }

The diagrams of triangles, Figs. 287 and 288, are now constructed by drawing short horizontal lines equal to the base lines of Fig. 286 with letters and numbers to correspond. Upon perpendiculars erected at one end of each of these lines the proper altitude is placed. The true lengths of the altitudes are plainly marked in Fig. 284.

The pattern development is started by drawing a straight line and setting off upon it a distance equal to the hypotenuse of triangle A to 1. Next in order comes triangle 1-B, so with point 1, Fig. 289, as a center and with a radius equal to the hypotenuse of triangle 1-B, an arc is drawn bearing away from point A. This is intersected at B by an arc drawn from point A, with a radius equal to line AB of Fig. 286.

With B as a center and a radius equal to the hypotenuse of triangle B-2, an arc is drawn bearing away from point 1. This is intersected by an arc drawn from point 1, with a radius equal to the distance 1-2 of Fig. 285, thereby establishing point 2 of the pattern. In this manner the entire half pattern is developed by following the order of triangulation, taking the spaces between the figures from Fig. 285, and the spaces between the letters from Fig. 286. Should the draftsman require a whole pattern, he would work both ways from the center line A-1, as the development progressed.