An undershot wheel, turned by the water passing beneath (Fig. 165), can be easily made. It can be of any desired size, and of any wood readily worked.

Before beginning work read carefully Marking, Rule, Square, Saw, and look up anyother references.

One like Fig. 166 can be made by simply nailing a set of small boards or paddles in a radial arrangement between two disks of wood. A dowel or broomstick will do for the shaft and should be fitted tightly in the hole bored through the wheel (see Boring), but should turn freely in the bearings at the side. It will make a rather neater job to shape the paddles as in Fig. 167, so that when put together the wheel will look like Fig. 166, but this is not at all necessary, and it will work just as well to make plain rectangular paddles and simply nail the disks on the outside edges (see Nailing). If you have no saw with which to get out the disks you can have them sawed at the mill, or you can work them out by describing the required circles and sawing a hexagon outside of the line with a common saw, when the circle can be finished with shave, hatchet, chisel, or knife (see Paring). Divide the circumference of each disk into as many parts as there are paddles and draw lines on the side to the centre, by which to nail the paddles in the right position. Start the nails on these lines and drive them nearly through before placing the paddles in position. Then nail one disk to the paddles, turn the wheel over and nail on the other disk. It is essential to a neat job that the paddles should all be of the same width. First make one edge straight. From this edge gauge the desired width on all the pieces (see Gauge) and saw or plane or trim, with knife, chisel, or shave, exactly to the line. If you make the paddles as shown in the cut, first square lines across at equal distances from one end (Fig. 167), and with a gauge set at a point equal to the thickness of the disks make lines parallel to each edge, and with the saw or saw and chisel, or even a knife, remove the pieces marked (see Paring).

Fig. 165.

Fig. 166.

Fig. 167.

The overshot wheel (Fig. 168) is harder to make, but is a livelier wheel. It is put together upon the same principle as the wheel just shown, except that the paddles, which do not project beyond the circumference of the disks, are not placed radially, but so that, with the addition of another set inserted to connect them, they form buckets.

Fig. 168.

Pig. 169.

To lay off the lines for the buckets, divide the circumference of each disk as before, and from the centre describe a small circle, as shown in Fig. 169. From the points on the circumference draw-lines tangent to the small circle. These lines will give the positions for the bottoms of the buckets. To complete the buckets mark from the circumference equal distances on these lines, and from these last points draw lines as ab to the next points on the circumference. First, nail together with only the bottoms of the buckets (on the lines cd). Then fit in the other pieces, to complete the buckets, on the lines ab. The ends of these last pieces should properly be bevelled (see Bevelling) to make a fairly tight joint. The rest of the work is the same as for the undershot wheel. A larger form (but harder to make) is suggested in Fig. 170. See note under Windmills, above.