Evening star. [volume] (Washington, D.C.) 1854-1972, 1931-03-12
M|LL|ONTH OF INCH
IS HELD IMPORTANT
Auto Industry Needs Most
Accurate Measurements,
Says Bureau.
BY THOMAS R. HENRY.

BY THOMAS r. HENRY.
Underwriting accuracy within less than
ten-millionths of an inch now is essen
tial in Americas standardized automo-
bile industry.
Anything greater than this minute
error might throw whole plant out Of
operation, as well as branch factories
scattered over the world, it is revealed
in the standards yearbook of the United
States Bureau of Standards, just issued.
Fineness of measurement which a few
years ago was only the dream of the
physical laboratory now has become a
necessary commonplace Of industry.
Accuracy Need Explained.
How this extreme accuracy is main
tanned is shown in a report by C..
Z. Johansson of the Ford Motor Co.
First the parts are checked by gauge
accurate to within eight-millionths of
an inch. This is checked every day and
sometimes every four hours, against an
inspection gauge accurate 10 within
four mlllionti1s of an inch. This in turn
Is checked frequently against labor
atory gauge accurate to within two
nlilliontns of an inch. Whenever the
working gauge In the hands CT the fac
tory inspector shows an error greater
than -millionths of an inch, it Is
immediately discarded.
"One guage worn to the point where
1t does not check the specified limits
properly" says Jollansson, may mean
in hour run several thousand defective
parts, stopping the operation of the
assembly line and retarding the pro-
duction activities of some branch in
distant part Of the world"
Temperature Important.
The necessary extreme accuracy, he
points out, requires that finer parts be
measured in a constant temperature
room because of the minute expansions
Of metals due to very slight temperature
changes. This room, in the Ford plant,
Is kept at 68 degrees farenheit. Ex-
periments revealed, he says, that an
increase of Is degrees from this con-
slant temperature increased the size
of the connecting rod 10 hundred
thousanths of an inch: Of the piston
90 hundred thounsandths; and of the
piston pin 10 red-thousandths. An
increase of % degrees increased the
size of the connecting rod IA hundred
thousandths Of an inch.
Minor Details Important.
Most of the standards now used in
the automobile industry apply to rel
atively minor details, reports DR.. Charles
F. Referring, president Of the General
Motors Research Corporation, who sees
little prospect of changes in the major
features of design, although such
changes might add to operating eff
cheney. Cars must be kept at relatively
their present width, he says, because of
the size of roads, and at their present
he Ar1.& h0fIlR-
wards sometimes are rutty with ice
and snow.
Even finer measurements now are
required as routine in other American
industries, the bureau reports. One
set of commercial length standards in
spected had a maximum error Of only
three ten-millionths of an inch. To
meet these increasing demands for
accuracy, the bureaus own equipment
must have an even greater accuracy.
Standard meter bars submitted from
physical laboratories for comparison
with the standard length unit kept at
Washington are tested to an accuracy
Of one micron, or thousandth part Of a
uillimeter.
Delicate Standards.
The most delicate length standards
now in general Use are made of
platinum alloy. The bureau announces
the determination Of superior mate
rial in an alloy of chromium and carbon
steel, which has the same heat eXpan-
sion as platinum and is superior in
hardness, rigidity and polishing quality.
For some of the finest length measures
the standard, extremely difficult TO use
is a certain wave length of light. For
short distances light wave measurements
have been co-ordinated with linear
measures to an accuracy Of one-balf
micron.
Accuracy in weight measurements of
one part in 1000, 900 with a new high
precision balance is announced. Among
| the notable advances has been the de-
termination of variability of standard
weights with changes in the humidity,
which Is believed to have brought about
serious errors in some laboratory
measurements in the past.
Electricity Measured.
Improvement of an old mechanism,
the bureau announces, now makes 1t
possible to measure the absolute value
of an electric current with a possible
error of only few parts in a million.
Meanwhile. the bureau announces, 1t
is cooperating with industrial labora-
; tories and government institutions in
England, France and Germany for the
establishment of other standards, deal
ing especially with light and electricity.
Among the new projects is the deter
mination of the absolute value Of gravity
at Washington for use Of the United
States Coast and Geodetic Survey, which
hitherto has used value Established
in Germany several years ego and which
is believed TO contain slight error
when applied to measurement in the
United States.