This is a good example of an article which follows the egg-shaped oval form. A sketch of the bath is shown in
Fig. 124, and on careful consideration of this and Fig. 125, the reader should find no trouble in understanding the composition of the bath surface.
The body of the bath is usually made up in three parts, the back and two side-pieces; the joints being respectively at the two sides and down the middle of the end.
On examining the plan and elevation in Fig. 125 it will be seen that the back of the bath is formed of part of a right cone, whilst the sides and end are built up from portions of two oblique cones. To obtain the construction lines for the back pattern first produce the lines 3 a and t k, to meet in the point c. This will give the apex of the cone of which t 3 may be considered to be the half-base. On t 3 describe a quarter-circle and divide it into three equal parts, dropping perpendiculars from each division point on to the line t 3. Join c to each of the points 1° and 2° and produce to meet the top line of the back t 3'. The pattern for the half-cone is now developed by using c 3 as a radius, and setting along a girth line (Fig. 126) equal to twice the length of the quarter-circle in the elevation. Radial lines are then drawn, passing through C and each numbered point on the girth line; these being cut off equal to the corresponding lengths taken from the elevation. Thus C 1", C 2", and C 3" are respectively equal to c 1', c 2' c 3' from the elevation. The points are joined up with a curve and thus will give the outline for the top part of back pattern. The radius C A for the bottom part will be taken from c a in the elevation. Allowances are put on the pattern for an edge, to which the bead is attached, a lap on the sides for grooves, and a single edge for the knock-up around the bottom. When worked up, the back, as set out, will come level across the top; in practice, however, the shoulders are brought round a little, and to do this the upper portion of the back pattern is very often formed by describing a semicircle on the line 0 0. The thick dotted line shows this semicircle on the pattern in Fig. 126. It will be seen that this latter method is much easier for marking the back pattern out, and gives a bolder look to the bath when made.
If it is required to make the bath so that the top of the back is to come some other shape, then all that is necessary is to draw an elevation of the particular shape, instead of the line t 3'. The construction lines c 1°, etc., would then be run up to meet this curve.
Instead of marking the side pattern (Fig. 123) out by the methods shown in Chapter XVIII (Articles Of Unequal Overhang. Oblique Cone). in connection with oblique cone surfaces, it will be simpler, in this ex-ample, to strike it out by the general method of triangu-lation. Turning again to the plan and elevation in Fig. 125, the curves b d of the bottom and f g of the top are each divided into three equal parts, and the lines numbered 1, 2, 3, etc., drawn, thus dividing the plan of the side and half-end into eight triangles. Imagine these are the plans of triangles, which lie on the surface of the bath, and it will readily be conceived that the pattern for this part can be obtained by adding together the true shapes of the eight triangles. To get the true lengths of the sides of the triangles set each of the numbered lines along from k, as shown. That is, make k 1, k 2, k 3, etc., equal respectively to the lines numbered 1, 2, 3, etc., on the plan. These points are then joined to t, and the lengths of lines for the pattern will be measured from the respective points up to t. Now turn to the side pattern (Fig. 128). Line number 1 is set down equal to 1 t, line number 2 equal to 2 t, and B L equal in length to the curve b l on the plan. The length F N equals f n, and the line number 3, or L N, equals 3 t, and so on for the other six triangles. When the points are connected up and the proper allowance added, as in the back plate, the pattern is complete.
The foot being equal-tapering can have its pattern struck out with very little trouble. The radius for the part of foot to go around the back of bath will be taken from p a. So that, on the pattern (Fig. 127), P A equals p a and P R equals p r; the length of the inner curve A A being equal to twice the length of the quarter-circle a b in plan. The side pattern of the foot (Fig. 125) is developed by first marking off k s equal to t d (the point t in this case being the centre from which the side curve of egg-shaped oval is described), and then drawing u s parallel to p a. The curve S B for the pattern is described with radius equal to u s and the part D B cut off equal in length to the arc d b in the plan. The distance k w is now set along the same length as e v (the radius for the small end of oval) and x w drawn parallel to p a. The centre W is determined by setting D W equal in length to x w; the arc D E then being drawn from this centre and cut off the same length as the curve d e in the plan. The width of the pattern will, of course, be the same as that for the back part, that is, D R will equal a r.
A pattern, showing the half-bottom, is drawn at the top of Fig. 125; the lines Z A and Z E being respectively equal in length to the lines z a and z e on the elevation. Allowance for a double edge is made all round the bottom to cover for knocking up on to the body.
A sketch, showing the arrangement of body, bottom, and foot, is shown at the lower part of Fig. 126. A good deal of care wants exercising in attaching the bottom to the body. After the bottom has been hollowed to the proper shape a flange about 1/2 in. wide should be set down all round. A single edge is then turned up to fit on the edge around the bottom of bath. After the bottom is slipped on, the paning down can be done with a paning hammer (Fig. 130), or, as is more generally the case, with a sheet metal worker's common hammer, as shown in Fig. 131. The knocking up of the joint can, of course, be done in the usual manner on a bench bar or otherwise.
A sketch explaining the arrangement of the bead is also shown on Fig. 129. The bead is usually made from a strip of sheet metal, being bent and curved in a beading machine. It can, however, be quite easily blocked up to the required shape with a suitable hammer on a lead block.
It is soldered to the edge of body and filling-in pieces are also soldered to the bead and body, as shown.
Sheet-metal lugs are fastened to the side of bath, as seen in Fig. 124; but these present no difficulty in marking out their shape or making.