thick (A, Figs. 1, 2 and 3) saw a circular opening 2-7/8 in. in
diameter. On each side of this block cut a larger circle 3-1/4 in.
in diameter, having the same center as the first circle (Fig. 3).
Cut the last circles only 1/4 in. deep, leaving the first circle
in the form of a ridge or track 3/8 in. wide, against which the
rubber tubing, E, is compressed by wheels. Bore two 1/4 in. holes
(HH, Fig. 1) from the outside of the block to the edge of the
inner circle. Put the rubber tube, E, through one of these holes,
pass it around the track and out through the other hole. Notice
the break (S) in the track; this is necessary in order to place in
position the piece holding the wheels.
Fig. 4 shows the wheel-holder, B. Make it of hard wood 3-1/8 in.
long, 1 in. wide and a little less than 7/8 in. thick, so that it
will run freely between the sides (Fig. 5) when they are placed.
Cut two grooves, one in each end, 1 in. deep and 1/2 in. wide. In
these grooves place wheels, CC, to turn on pins of stout wire.
These wheels should be 3/4 in. in diameter. When placed in the
holder their centers must be exactly 2 in.
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