For a practical drawing the form must be shown in elevation and not in perspective. All the horizontal divisions must be drawn in parallel lines. It is obvious that except for profiles and general height, further details must be given for a working drawing.
The Segment or Stretch Out
No. 225. Stretch Out of the Cone.
In designing for forms in the round it is necessary to detail the ornament on a segment or a stretching-out of the area. This is easily done in the case of a cylinder of which the height is evident, and the extreme width and circumference easily obtainable. If the object is not in existence for direct measurement the width can be determined from the diameter as expressed in the drawing. As this diameter is about one-third of the circumference a parallelogram three times the width of the diameter will provide, in the flat, the complete area on which detail has to be drawn.
Should the shape of the object be that of a truncated cone—that is, with straight inclined sides and a circular plan, the procedure must necessarily be different. In this case the lines of the sides should be extended till they intersect. This intersection forms a centre from which arcs may be struck coinciding with the lines of top and base. The greatest diameter should be set off on each side of the elevation on the larger radius and the points joined up with the centres from which the arcs were struck. The result is a fan-shaped figure bounded by these outer lines and the two arcs. This figure gives the entire area of the surface of the truncated cone.
In either of the figures thus obtained for designing detail on, the surfaces can be sub-divided. For instance, if the decoration consists of a unit repeated three or six times round the form, it will not be necessary to reproduce the whole area, provided always that the profiles are straight or tapered.
