El Paso herald. (El Paso, Tex.) 1901-1931, 1915-05-29
ACCURACY IN
MAKING MOTORS
MachinistssTest the Various
Parts Down to One One
thousandth of Inch.

One one-thousandth Of an inch is a
difference so small that should the va
riOus parts OF motor vary rom the
standard measurement by several times
that amount il would seem that 1t
would make no difference-especial
when that motor is large enough TO
propel an automobile Yet a difference
OF one One-thOusandth OF an inch IS
Just the difference between success and
failure For that reason a large num-
Der OF the inspectors OF finished parts
at an automobile factory spend all their
working hours testing with microme-
tiers that measure with scale IN thOus-
andths Of an inch
What would happen II an inspector
passed a part that varied more than
one one-thousandth Of an inch2 To be
perfectly frank, the purchaser would
not get what he pays for. He pays for
a motor that viii not wear unduly-
for, in time any motor viii show signs
OF wear; that is why so many parts OF
a good motor are adjustable. But where
there is a discrepancy OF more than
one One-thousandth Of an inch then the
wear begins Immediately in an uneven
manner. which means rapid deteriora-
ton.
With care that gives such accuracy
the result is a motor with a smooth,
silent flow of power. making one in the
machine feel as il riding through the
air And because Of this accuracy in
construction, the car continues TO run
smoothly. silently. and powerfully
month after month A perfectly ad-
justed motor runs noiselessly. except
for the Sound OF gas in the carburetor
and the passage Of exhaust through the
muffler.
The flywheel OF a motor must be
balanced TO perfection. 1t is cast OF
special fine gray iron, then il is put
in a machine and turned to a perfect
roundness- The center is then bored
out with perfect accuracy in reference
TO the circumference. In a test. II il
develops that there is the fraction Of
an ounce difference in the weight OF
any side Of a wheel the workman bOres
is brought exactly 10 a balance. When
his work is finished. the flywheel is as
perfectly balanced as the balancewheeI
o. a watch
which admit the bolts that fasten the
fyWheel TO the crank shaft has a gage
so finely adjusted that between the
go and won't go marks on il there
is only a difference Of three-quarters
OF one one hOusandth OF an inch Yet
there are finer divisions still The
pushrods and pushrod guides must be
accurate within one-half Of one one
thousandth OF an inch. SO must be the
wheel bearings on the four aNles And
even these have twice the leeway that
some other parts possess
The Wristpin on the connecting rods
viii not be passed by an inspector II it
Is more than One-fourth OF one one
thousandth Of an inch over or under
the standard measurement The round
crankpinS on the crankshaft cannot lie
out Of round" more than that minute
fraction of an inch if they are to pass
inspection When il is borne in mind
that an ordinary sheet OF writing paper
has a thickness Of from two to four
one-thOusandths Of an inch, the mar
TelOus accuracy Of manufacture % -
motor may be imagined. Here are parts
OF the machine that must not vary
from the true more than one-eighth TO
the thickness OF a sheet
OF writing paper
Time gears must mesh within one
one-thOusandth Of an inch. The accu-
racy Of inspection may readily be un-
derstOod- There are machines in op-
GRAFTON which bore "A holes in a cylin-
der casting In one operation These
holes In each cylinder bear exactly the
same relation 20 each other, because
the boring mechanism is always guided
through jigs that viii not admit Of one
one-thousandth part Of an inch differ
ence In any two operations. These ma
chimes cost SIS o00 each.
Cylinders are reamed out after they
are cast These roaming machines.
which operate through jigs with un-
varying accurac TO one one-thOus-
andth Of an inch cost $4,000 each.