If we
draw the line _w_ we can see in what proportion the measurement should
be made between the outer diameter of the cylinder and the measure of
the half shell. It will be seen on measurement that the distance between
the center _e_ and the line _w_ is about one-fifteenth part of the outer
diameter of the cylinder and consequently with a cylinder which measures
45/1000 of an inch in diameter, now the half shell should measure half
of the entire diameter of the cylinder plus one-fifteenth part of such
diameter, or 251/2 thousandths of an inch.
After these proportions are understood and the drawing made, the eye
will get accustomed to judging pretty near what is required; but much
the safer plan is to measure, where we have the proper tools for doing
so. Most workmen have an idea that the depth or distance at which the
cylinder is set from the escape wheel is a matter of adjustment; while
this is true to a certain extent, still there is really only one
position for the center of the cylinder, and that is so that the center
of the pivot hole coincides exactly with the center of the chord to the
curve of the impulse face of the tooth or the point _e_, Fig.
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