This section is from the book "Practical Sheet And Plate Metal Work", by Evan A. Atkins. Also available from Amazon: Practical Sheet And Plate Metal Work.

An elevation which illustrates this method of constructing a head is shown in Fig. 215; the body being divided into three segments, A, B, and C.

The patterns for two of the parts are shown set out, and after what has been said in connection with Fig. 214, it will be sufficient to briefly indicate the method of obtaining one pattern, say, for segment A. The back and throat curves are each divided into three equal parts, and the joint lines drawn. On these semicircles are described and divided into, say, four equal parts. Now to deal with the lines required for the pattern of segment A. From each of the division points of the semicircle, which is described on 0 4, drop perpendiculars on to that line, and from the feet of these perpendiculars run lines down square to a e and across it, cutting them off equal in length to the corresponding lines on the semicircle. There is no need to join the joints so found; but if they are connected together it will be seen that they form a semi-ellipse as in Fig. 244. The mid-line 4 e of the pattern will, of course, be made the same length as 4 e in the elevation. Now fix the compasses to e 3' and set this distance along the base line from e' and so determine the point 3". The line 3" 3° will give the required length of e 3 for the pattern. Next measure d 3' and set this along the base line from e', and so obtain the point d'. The line d' 3° will then be the length required for the line d 3 on the pattern. In the same manner the lengths of all the other lines required to construct the eight different triangles on the half-pattern can be obtained. The lengths e d, 4 3, etc., will be taken from the lengths of one of the parts on the respective semicircles, as in Fig. 214.

All the construction lines actually required to strike out the pattern for the piece B are shown on the elevation; but as the marking out is only a repetition of that already gone over for segment A, there is no need for any further description. The pattern for C is not shown; but this will, of course, come out in the same manner as for the other segments.

If the backs of each segment are to be left straight (which is sometimes done in very common heads), as in Fig. 214. then the patterns as laid out in Fig. 215 will be quite correct; but if they are to be hollowed to the required curve, then it will give a more accurate result to produce the joint lines out to the dotted lines of the backs, and describe the semicircles on these, thus making allowance for the draw-ing-in of the backs of the segments somewhat in hollowing.

As pointed out in connection with the pattern for Fig. 214, it should also be noted that there is no need to draw a single construction line on the pattern, all that is wanted being the points obtained by the intersection of the arcs. The construction lines are simply shown to illustrate the principle of setting out the pattern.

No allowance for jointing has been made, as this can be added according to requirements.

The method of fixing the split-tube to form the bead around the mouth is also shown in an enlarged view on Fig. 215.

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