The eccentric may be built up from a metal disc about 3/4 inch diameter and
two slightly larger discs soldered concentrically to the sides. The width
of the middle disc should be the same as that of the eccentric rod. A
careful filer could make a passable eccentric by sinking a square or
semicircular groove in the edge of a wide disc. The centre of the eccentric
must be found carefully, and a point marked at a distance from it equal to
half the travel of the valve. To ascertain this, pull the valve forward
until the steam port is fully exposed, insert a bar at the rear end of the
valve tube, and mark it. Then push the valve back until a wire pushed
through the port from the cylinder side shows that the port is again fully
exposed. Insert and mark the bar again. The distance between the marks
gives you the "travel" required.
Order of Assembly.--The following list of operations in their order may
assist the beginner:
Make the bed.
Cut out cylinder barrel, piston, and valve tube.
Bevel off the ends of the last inside to allow the valve to enter easily.
Make the valve.
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