For this construction draw a circle c, [Fig. 2792], and divide it into as many equal points of division as there are to be arms in the wheel. From these points of division draw lines to the centre, and these lines will show the required bevel at the end of each spoke, as shown in the figure. The ends should be verified for bevel by striking from the common centre a second circle, as d; and measuring if the arms are equidistant, measured at the circle and from the edge of the arm to that of the next, finished along the full length. When fitted, corrected, glued and dry, the spokes may be let into the wheel and a recess turned into the centre to receive the hub.
The rim and all parts that can be got at may then be turned in the lathe, the pattern then being reversed in the lathe to turn the inside of the rim, or the other side of the spokes, when the job will be complete. When, however, the rim is to be a very thin one, it may be necessary to fasten the segments together at the ends by other means as well as glue, hence a saw-cut may be made in each end, and a tongue inserted.
It is obvious that each half of the pattern is constructed by similar segments, the line of parting being through the centre of the arms, as at a b, in [Fig. 2791]. To keep the two halves coincident when in the mould, pins are inserted in the rim and arms of one half, fitting closely into holes provided in the other half.
To construct a pattern for a pipe, the pattern would be made in two halves, and constructed of what are termed staves, that is, pieces of wood running lengthways of the pipe. The number of these staves is optional, save that it must be even, so that each half pattern will contain an equal number.
Fig. 2793.
Let it be required to make a pattern for a pipe 18 inches in diameter, and to be 1 inch thick. Draw the line a b, [Fig. 2793], and from a point on it, as c, draw a semicircle a b, equal in diameter to the diameter of the outside of the pipe. Also the circle d e f, equal to the diameter of the inside of the pipe, and these will represent an end view of the pipe. Divide these semicircles into as many equal divisions as it is decided to have staves in the half pattern—as 1, 2, 3, 4, 5, 6; and from one of these divisions make a template as denoted by the oblique lines at 2, leaving it slightly larger than the division, to allow stuff to work on in fitting the staves, &c.
