e stay is attached, having been previously chipped plumb and level.
The stake wedges with which the framing is set up preparatorily to the
operation of scribing, must be set so as to support equally the
superincumbent weight, else the framing will spring from resting unequally,
and it will be altogether impossible to fit it well. These directions
obviously refer exclusively to the old description of side lever engine
with cast iron framing; but there is more art in erecting an engine of that
kind with accuracy, than in erecting one of the direct action engines,
where it is chiefly turned or bored surfaces that have to be dealt with.

720. _Q._--How do you lay out the positions of the centres of a side lever
engine?

_A._--In fixing the positions of the centres in side lever engines, it
appears to be the most convenient way to begin with the main centre. The
height of the centre of the cross head at half stroke above the plane of
the main centre is fixed by the drawing of the engine, which gives the
distance from the centre of cross head at half stroke to the flange of the
cylinder; and from thence it is easy to find the perpendicular distance
from the cylinder flange to the plane of the main centre, merely by putting
a straight edge along level, from the position of the main centre to the
cylinder, and measuring from the cylinder flauge down to it, raising or
lowering the straight edge until it rests at the proper measurement. The
main centre is in that plane, and the fore and aft position is to be found
by plumbing up from the centre line on the sole plate. To find the paddle
shaft centre, plumb up from the centre line marked on the edge of the sole
plate, and on this line lay off from the plane of the main centre the
length of the connecting rod, if that length be already fixed, or otherwise
the height fixed in the drawing of the paddle shaft above the main centre.
To fix the centre for the parallel motion shaft, when the parallel bars are
connected with the cross head, lay off from the plane of main centre the
length of the parallel bar from the centre of the cylinder, deduct the
length of the radius crank, and plumb up the central line of motion shaft;
lay off on this line, measuring from the plane of main centre, the length
of the side rod; this gives the centre of parallel motion shaft when the
radius bars join the cross head, as is the preferable practice where
parallel motions are used. The length of the connecti