The setting-out as shown in Fig. 190 needs little explanation. The girth as taken from the section is first laid out, and construction lines drawn through each division point, these being cut off by the respective distances as shown projected down. In practice, it might be here remarked, this method of projecting lengths is hardly permissible, on account of the liability of error and inconvenience of drawing long lines parallel. The lengths should be measured from the section shape and transferred directly to the pattern. It will be sufficient, in practice, to mark out a piece like the shaded portion on the pattern, as this can be used as a template to strike out the remaining part by reversal.

Ridge Cap Elbow 207

Fig. 190.