Sketches and drawings of conical and shaped parts
A sketch is a hand-drawn picture of a part, without instruments but keeping proportions; a drawing is made accurately with instruments to scale and shows all dimensions. On a conical part’s drawing the big diameter D, small diameter d and cone length l are given. If the slope angle is not shown, it can be found by the formula tg α = (D − d) : (2 · l), where α is the slope angle of the cone. Scale is the ratio of a drawn size to the real size: at a scale of 1 : 2 a real length of 120 mm is 60 mm on the drawing. When drawing a shaped part, first the axis line is drawn, then the cylindrical, conical and spherical sections one after another along the axis, with dimensions on dimension lines. After the sketch comes the drawing, and from it the technological map is prepared. With pencils, rulers and compasses mind the sharp points: keep the compass point away from your face and close it when walking.
Drawing workshop: each pair sketches and draws (1 : 1) a conical part with a bottom diameter of 40 mm, top of 20 mm and length 60 mm, adds dimensions and calculates tg α ((40 − 20) : 120 for a length of 60 mm).