Fig. 2794.
Now, when the staves are cut out it is necessary to have some kind of a frame or support to hold them while jointing them; hence, draw also from the points of division, as d, e, f, the lines a, b, c, d, e, f, and these will form the sides of a half-disk polygon, whose diameter is from d to f. A sufficient number of these polygonal half-disks are cut out to stand about two feet apart along the whole length of the pipe, as in [Fig. 2794], and on these, temporarily fastened to the board b, the staves are jointed and fastened together by glue while each stave is held to its place on each half-disk by a screw. The top stave may be put on first, as it will act as a stay to the half-disks. If the pipe is so long that it is composed of more than two pieces, the end pieces should be put on first, and the intervening space filled up last, which enables the ends to abut firmly. The second half may be added to the first one, putting a piece of paper between the edges of the two to prevent their sticking together.
If the pipe has a bend, it is built up separately, instead of being formed of staves, the process being as follows:—
Fig. 2795.
Fig. 2796.
In [Fig. 2795] let b represent the centre of the bend curve, the line c representing one end, g the other end, h the inner and j the outer arc of the bend. Let it be determined to build up the bend in five pieces, as shown at 1, 2, 3, 4, 5, which represents an end view of the half pattern. Templates are then made for each of the pieces 1, 2, &c., being formed as denoted by the oblique lines, whose dimensions slightly exceed the half circle e of the pattern, to allow wood for dressing up. To find the curve for these pieces, set the compasses to a radius from b to the outer corner of piece 1, and draw the arc k. Set the compasses to the radius from b to the inner corner of piece 1, and draw the arc l, and the space between these two arcs, which space is marked 1 t, is a template for the curve of piece 1. By a similar process applied to pieces 2, 3, 4 and 5 similar templates for their respective curves are obtained; and selecting timber of a proper thickness, we mark out the respective curves from these templates, which may be of thin board or of stiff paper. In putting these pieces together the lower ones are set to lines forming a plan of the bend, being set a little outside the lines to allow wood for truing the pieces to shape after they are put together. The lower pieces are temporarily fixed to the board on which the plan is marked, and the upper ones fastened to the lower by glue, the joint surfaces of each line being planed true previous to being glued. It is a great assistance, however, to cut out two half circles, representing the ends of the pipe, and to place them on the board to build upon. When a bend of this kind occurs in a covering for a pipe that is exposed to view, it is necessary, for the sake of appearance, to have the pieces composing the bend to correspond with those on the straight part of the pipe, as shown in [Fig. 2796]. The part a would be got out in staves, as described for the pattern of a pipe. The bend b would be also got out as described for that figure for a bend, save that the number of staves for the bend would equal the number on the pipe. But in this case each stave should be fitted to its fellow by pins, or its edge fitting into dowels on the edge of its fellow; thus one edge of a stave would have the dowels and the other the pins; the whole, when finished, being bound together by metal bands, as shown in the figure.