Perhaps the most complicated patterns to mark out are those for objects where the two parts fitting together are both conical. Such a case is shown in Fig. 321.

As usual the first thing to do is to locate points on the joint or curve of intersection, and when this is done the ordinary method of getting out a pattern for a part cone (Chapter XIV.) can be applied.

Conical Spout Fitting On Conical Vessel 358

Fig. 3-1.

The obtaining of one point (p) only is shown, as all the others will be found in exactly the same manner. The centre line t n of the spout cone is first drawn and r s divided into four equal parts, and lines drawn across as shown by a b and the others. The middle point, c, of a b is next determined and the line e d drawn through it square to t n. A quarter-circle is constructed on e d, and c o drawn parallel to e n. The line c m is next drawn perpendicular to a b and cut off equal to c o. The quarter ellipse, a g m, is now constructed by the trammel method (Chapter XXI (Elliptical Work. Construction Of Ellipse).), and the point g determined by describing the quarter-circle on l k to intersect the ellipse. A perpendicular is now run up from g to cut a b in p; which will be a point on the elevation of joint curve. In the same way points can be found on the other two lines.

There is no need to describe the marking out of the spout pattern, as this is done in former chapters, but the method of obtaining the shape of the hole on the body pattern is worth considering. Mark off H L equal to h l, and draw around the arc, cutting off L G equal in length to the arc l g on the elevation. In the same way other points can be found which, when joined up, will give the shape of the hole.