There are many different kinds of elliptical coal-buckets, one of the commonest being that known as a "Waterloo," a sketch of which is shown in Fig. 169. To set the pattern out for the body of this is generally considered a somewhat difficult task. With careful consideration, however, and some understanding of the principles of development, the reader should find the difficulties disappear.
In the example as set out in Fig. 170 it is assumed that the back and the front of the bucket have the same taper:
hence the body will come out as a portion of an elliptical cone. The elevation is drawn as shown, and the end lines produced to meet in T. The centre line T t is drawn square to 6 0, and produced to 3'. The semi-ellipse is described and divided into six equal parts, perpendiculars being dropped from each division point on to 6 0. Through the feet of these perpendiculars lines are drawn from T and produced to the top curve of the elevation, thus obtaining the points 1', 2', 3', etc. The points 1, 2, 3, etc., on the semi-ellipse are then swung about t on to the line 6 0, these latter points being joined to T, and the lines produced upwards to meet the horizontals drawn through the points on the top curve of the elevation. Thus, 5" is obtained by connecting T to 5° and producing to meet the horizontal line drawn through 5'. In the same way the other points 1", 2", etc., are fixed.
Now for the pattern. The curve 0 0 (Fig. 170) is obtained in exactly the same way as that on Fig. 168, the length of lines A 0, A 1, etc., being measured from T up to the base line 6 0. Thus A 5 equals T 5°, and so for other corresponding lines. The pattern construction lines are then drawn from A through each point and produced outwards. These radial lines are cut off to their proper lengths by taking corresponding lengths from the elevation. Thus A a = T 0", A b = T 1", A c = T 2", and so for the rest of the points.
Allowance for wiring is added to the top end of pattern, for throwing off and knocking up on the bottom, and grooving on the sides.
The pattern for the foot is laid out exactly as in Fig. 168, the point c on the elevation (Fig. 170) representing the apex of the elliptical cone. For the inner curve, the lengths are measured from c down to the line 6 0, and for the outer curve down to the bottom line. Thus, C 5 and C h on the pattern are respectively the same length as c 5° and c h on the elevation.
Allowance is made for wiring on the outer part, a single edge on the inner, and for grooving or riveting on the ends. Details of the methods of attaching the bottom and foot to body are also shown on Fig. 170. If made of black sheet iron the bottom edge is annealed by running around in the fire, after which it is (1st) carefully thrown off by stretching, and annealed again. The flange is then levelled with a mallet and (2nd) edged over. The bottom (3rd) is slipped in, and after a single edge has been turned on the foot this, also, is put in and (4th) paned down, the latter operation being best performed on a bick-iron and then run around on a hatchet-stake. The final operation (5th) is the doubling-over, or knocking up, as shown in Fig. 171. A special knocking-up hammer is used, and the bench-stake being either a head, as shown, the back end of a side-stake, or the end of a bench-bar.
Whilst the illustration (Fig 171) shows the knocking-up process on a coal-bucket, this method of attachment, it may be pointed out, is very commonly applied to a large number of sheet-metal articles.