MACHINERY’S REFERENCE SERIES

EACH NUMBER IS ONE UNIT IN A COMPLETE LIBRARY OF
MACHINE DESIGN AND SHOP PRACTICE REVISED AND
REPUBLISHED FROM MACHINERY

NUMBER 21

MEASURING TOOLS

Third Edition

CONTENTS

Copyright, 1910, The Industrial Press, Publishers of Machinery.
49-55 Lafayette Street, New York City

CHAPTER I

HISTORY AND DEVELOPMENT OF STANDARD MEASUREMENTS^[1]

While every mechanic makes use of the standards of length every day,
and uses tools graduated according to accepted standards when performing
even the smallest operation in the shop, there are comparatively few who
know the history of the development of the standard measurements of
length, or are familiar with the methods employed in transferring the
measurements from the reference standard to the working standards. We
shall therefore here give a short review of the history and development
of standard measurements of length, as abstracted from a paper read by
Mr. W. A. Viall before the Providence Association of Mechanical
Engineers.

Origin of Standard Measurements

By examining the ruins of the ancients it has been found that they had
standard measurements, not in the sense in which we are now to consider
them, but the ruins show that the buildings were constructed according to
some regular unit. In many, if not all cases, the unit seems to be some
part of the human body. The “foot,” it is thought, first appeared in
Greece, and the standard was traditionally said to have been received
from the foot of Hercules, and a later tradition has it that Charlemagne
established the measurement of his own foot as the standard for his
country.

Standards Previous to 1800

In England, prior to the conquest, the yard measured, according to
later investigations, 39.6 inches, but it was reduced by Henry I in 1101,
to compare with the measurement of his own arm. In 1324, under Edward II,
it was enacted that “the inch shall have length of three barley corns,
round and dry, laid end to end; twelve inches shall make one foot, and
three feet one yard.” While this standard for measurement was the
accepted one, scientists were at work on a plan to establish a standard
for length that could be recovered if lost, and Huygens, a noted
philosopher and scientist of his day, suggested that the pendulum, which
beats according to its length, should be used to establish the units of
measurement. In 1758 Parliament appointed a commission to investigate and
compare the various standards with that furnished by the Royal Society.
The commission caused a copy of this standard to be made, marked it
“Standard Yard, 1758,” and laid it before the House of Commons. In 1742,
members of the Royal Society of England and the Royal Academy of Science
of Paris agreed to exchange standards, and two bars 42 inches long, with
three feet marked off upon them, were sent to Paris, and one of these was
returned later with “Toise” marked upon it. In 1760 a yard bar was
prepared by Mr. Bird, which was afterwards adopted as a standard, as we
shall see later.

In 1774 the Royal Society offered a reward of a hundred guineas for a
method that would obtain an invariable standard, and Halton proposed a
pendulum with a moving weight upon it, so that by counting the beats when
the weight was in one position and again when in another, and then
measuring the distance between the two positions, a distance could be
defined that could at any time be duplicated. The Society paid 30 guineas
for the suggestion, and later the work was taken up by J. Whitehurst with
the result that the distance between the positions of the weight when
vibrating 42 and 84 times a minute was 59.89358 inches. The method was
not further developed.

How the Length of the Meter was Established

In 1790, Talleyrand, then Bishop of Autun, suggested to the
Constituent Assembly that the king should endeavor to have the king of
England request his parliament to appoint a commission to work in unison
with one to be appointed in France, the same to be composed of members of
the Royal Society and Royal Academy of Science, respectively, to
determine the length of a pendulum beating seconds of time. England did
not respond to the invitation, and the French commission appointed
considered first of all whether the pendulum beating seconds of time, the
quadrant of the meridian, or the quadrant of the equator should be
determined as a source of the standard. It was decided that the quadrant
of the meridian should be adopted and that 0.0000001 of it should be the
standard.

The arc of about nine and one-half degrees, extending from Dunkirk on
the English Channel to Barcelona on the Mediterranean and passing through
Paris, should be the one to be measured. The actual work of measuring was
done by Mechain and Delambre according to the plans laid down by the
commission. Mechain was to measure about 25 per cent of the arc, the
southern portion of it, and Delambre the remainder; the reason for this
unequal division was that the northern division had been surveyed
previously, and the territory was well-known, whereas the southern part
was an unknown country, as far as the measurement of it went, and it was
expected that many severe difficulties would have to be surmounted. The
Revolution was in progress, and it was soon found that the perils
attending the measurement of the northern part were greater than those
attending the southern part of the territory. The people looked askance
at all things that they did not understand, and Delambre with his
instruments was looked upon as one sent to further enthrall them. He was
set upon by the people at various times and although the authorities
endeavored to protect him, it was only by his own bravery and tact that
he was able to do his work and save his life. The Committee of Safety
ordered that Mechain and Delambre close their work in 1795, and it was
some time afterward before it was resumed.

Having completed the field work, the results of their labors were laid
before a commission composed of members of the National Institute and
learned men from other nations, who had accepted the invitation that had
been extended to them, and after carefully reviewing and calculating the
work, the length of the meridian was determined, and from it was
established the meter as we now have it. A platinum bar was made
according to the figures given, and this furnishes the prototype of the
meter of the present time. Notwithstanding all of the care taken in
establishing the meter, from work done by Gen. Schubert, of Russia, and
Capt. Clarke, of England, it has been shown that it is not 0.0000001 of
the quadrant passing through Paris, but of the one passing through New
York.

The Standard Yard in England—Its Loss and Restoration

Whether incited by the work of the French or not, we do not know, but
in the early part of this century the English began to do more work upon
the establishment of a standard, and in 1816 a commission was appointed
by the crown to examine and report upon the standard of length. Capt.
Kater made a long series of careful observations determining the second
pendulum to be 39.1386 inches when reduced to the level of the sea. This
measurement was made on a scale made by Troughton—who, by the way,
was the first to introduce the use of the microscope in making
measurements—under the direction of and for Sir Geo. Schuckburgh.
In 1822, having made three reports, after many tests, it was recommended
that the standard prepared by Bird in 1760, marked “Standard Yard, 1760,”
be adopted as the standard for Great Britain.

The act of June, 1824, after declaring that this measure should be
adopted as the standard, reads in Sec. III.: “And whereas it is expedient
that the Standard Yard, if lost, destroyed, defaced or otherwise injured
should be restored to the same length by reference to some invariable
natural Standard; and whereas it has been ascertained by the
Commissioners appointed by His Majesty to inquire into the Subjects of
Weights and Measures, that the Yard, hereby declared to be the Imperial
Standard Yard, when compared with a Pendulum vibrating Seconds of Mean
Time in the latitude of London, in a Vacuum at the Level of the Sea, is
in the proportion of Thirty-six Inches to Thirty-nine Inches and one
thousand three hundred and ninety-three ten thousandth parts of an Inch;
Be it enacted and declared, that if at any Time hereafter the said
Imperial Standard Yard shall be lost, or shall be in any manner
destroyed, defaced or otherwise injured, it shall and may be restored by
making a new Standard Yard bearing the same proportion to such Pendulum,
as aforesaid, as the said Imperial Standard Yard bears to such
Pendulum.”

It was not long after this act had been passed, if indeed not before,
that it became known that the pendulum method was an incorrect one, as it
was found that errors had occurred in reducing the length obtained to
that at the sea level, and despite the great pains that had been taken,
it is doubtful if the method was not faulty in some of its other
details.

When the Houses of Parliament were burned in 1834, an opportunity was
offered to try the method upon which so much time and care had been
spent. A commission was appointed and to Sir Francis Baily was assigned
the task of restoring the standard. He did not live to complete the task,
dying in 1844. He succeeded in determining the composition of the metal
that was best adapted to be used, which metal is now known as Baily’s
metal.

Rev. R. Sheepshanks constructed a working model as a standard and
compared it with two Schuckburg’s scales, the yard of the Royal Society,
and two iron bars that had been used in the ordnance department. Having
determined to his own satisfaction and that of his associates the value
of the yard, he prepared the standard imperial yard, known as Bronze No.
1, a bronze bar 38 × 1 × 1 inch, with two gold plugs dropped into holes
so that the surface of the plugs passes through the center plane of the
bar. Upon these plugs are three transverse lines and two longitudinal
lines, the yard being the distance from the middle transverse
line—the portion lying between the two longitudinal ones—of
one plug, to the corresponding line on the other plug. Forty copies were
made, but two of these being correct at 62 degrees Fahrenheit, and these
two, together with the original and one other, are kept in England as the
standards for reference. In 1855 the standard as made by Rev. Sheepshanks
was legalized.

Attempts to Fix a Standard in the United States

The Constitution empowers Congress to fix the standards of weights and
measures, but up to 1866 no legal standard length had been adopted. In
his first message to Congress Washington said: “A uniformity in the
weights and measures of the country is among the important objects
submitted to you by the Constitution, and if it can be derived from a
standard at once invariable and universal, it must be no less honorable
to the public council than conducive to the public convenience.”

In July, 1790, Thomas Jefferson, then Secretary of State, sent a
report to Congress containing two plans, both based on the length of the
pendulum, in this case the pendulum to be a plain bar, the one plan to
use the system then existing, referring it to the pendulum as the basis,
and the other to take the pendulum and subdivide it, one-third of the
pendulum to be called a foot. The whole length was that of one beating
seconds of time. He made a table to read as follows:

Congress did not adopt his system, and as England was then working on
the problem, it was decided to await the results of its labors. In 1816,
Madison, in his inaugural address, brought the matter of standards to the
attention of Congress, and a committee of the House made a report
recommending the first plan of Jefferson, but the report was not acted
upon. In 1821, J. Q. Adams, then Secretary of State, made a long and
exhaustive report in which he favored the metric system, but still
advised Congress to wait, and Congress—waited.

What the Standards are in the United States

The standard of length which had generally been accepted as the
standard, was a brass scale 82 inches long, prepared by Troughton for the
Coast Survey of the United States. The yard used was the 36 inches
between the 27th and 63d inch of the scale. In 1856, however “Bronze No.
11” was presented to the United States by the British government. This is
a duplicate of the No. 1 Bronze mentioned before, which is the legalized
standard yard in England. It is standard length at 61.79 degrees F., and
is the accepted standard in the United States. A bar of Low Moor iron,
No. 57, was sent at the same time, and this is correct in length at 62.58
degrees F. The expansion of Bronze No. 11 is 0.000342 inch, and that of
the iron bar is 0.000221 inch for each degree Fahrenheit. While the yard
is the commonly accepted standard in this country, it is not the legal
standard. In 1866 Congress passed a law making legal the meter, the first
and only measure of length that has been legalized by our government.
Copies of the meter and kilogram, taken from the original platinum bar at
Paris, referred to before, were received in this country by the President
and members of the Cabinet, on Jan. 2, 1890, and were deposited with the
Coast Survey. By formal order of the Secretary of the Treasury, April 5,
1893, these were denominated the “Fundamental Standards.”

The International Bureau of Weights and Measures

After the original meter was established, it was found that copies
made by various countries differed to a greater or less extent from the
original, and believing that a copy could be made from which other copies
could be more readily made than from the end piece meter, and that better
provision could be made for the preservation of the standard, France
called a convention of representatives from various States using the
system, to consider the matter. The United States representatives, or
commissioners, were Messrs. Henry and Hildegard, who met with the general
commission in 1870. The commissioners at once set at work to solve the
problem presented to them, but the Franco-Prussian war put an end to
their deliberations. The deliberations were resumed later, and May 20,
1875, representatives of the various countries signed a treaty providing
for the establishment and maintenance, at the common expense of the
contracting nations, of a “scientific and permanent international bureau
of weights and measures, the location of which should be Paris, to be
conducted by a general conference for weights and measures, to be
composed of the delegates of all the contracting governments.”

This bureau is empowered to construct and preserve the international
standards, to distribute copies of the same to the several countries, and
also to discuss and initiate measures necessary for the determination of
the metric system. The commission adopted a form for the standard as
shown in Fig. 1. The lines representing the length of the meter are drawn
on the plane A, which is the neutral plane, and will not change in
length should the bar deflect. The bar is made of 90 per cent platinum
and 10 per cent iridium, about 250 kilograms having been melted when
preparations were made for the first standard, so that all of the copies
made from this cast represent the same coefficient of expansion and are
subject to the same changes as the original. The French government
presented to the bureau the pavilion Breteuil, opposite the Park of St.
Cloud, which was accepted and put into order and is now the repository of
the originals of the meter and the kilogram. The expense attending the
first establishment of the bureau was about $10,000 to the United States,
and since then its share of the annual expense has been about $900. The
standards in the possession of the United States were received through
the international bureau.

The Commercial Value of a Standard

Having at the disposal of the nation a standard of length, the
question arises, “What can be made of it commercially, and how do we know
when we have a copy of the standard?”

Fig. 1. Form of Bar Adopted for International Standards of Length

In 1893, the Brown & Sharpe Mfg. Co. decided to make a new
standard to replace the one they had at that date. Mr. O. J. Beale was
detailed to do this work. He prepared steel bars about 40 inches long by
1¼ inch square, and after planing them, they were allowed to rest for
several months. At the ends of these bars he inserted two gold plugs, the
centers of which were about 36 inches apart, and a little beyond these
two others about one meter apart. A bar was placed in position upon a
heavy bed. This was so arranged that a tool carrier could be passed over
the bar. The tool carrier consisted of a light framework, holding the
marking tool. One feature of the marking was that the point of the
marking tool was curved and had an angle, so that if dropped it made an
impression in the form of an ellipse. In graduations, ordinarily, the
line, when highly magnified, is apt to present at its ends an impression
less definite than in the center, by reason of the form of the objective.
The line made with the tool mentioned is short, and that portion of the
line is read which passes, apparently, through the straight line in the
eye-glass of the microscope. In order to make these lines as definite as
possible, the point was lapped to a bright surface. After being placed in
position, the microscope, which could be placed on the front of the tool
carrier, was set to compare with the graduation on the standard bar from
which the new bar was to be prepared. After such a setting the readings
were made by three persons, and by turning the lever the marking tool was
dropped, making a very fine line, so fine indeed, that when the
authorities in Washington began the examination of the bar later on they
declared that no line had been made upon these studs.

After making the first line, the carriage was moved along to compare
with the other line on the standard, and after the correction had been
made by the use of the micrometer in the microscope, the marking tool was
again dropped, giving the second line, which was intended to mark the
limit of one yard over-all. The same operation was repeated in the
marking of the meter. The whole of this work was done, of course, with
the greatest care, and, while the theoretical portion of it appears very
simple in detail, it required a great deal of time and patience before
the last line had been made. The bar thus marked was taken to Washington,
and in Mr. Beale’s presence was compared by the attendants with Bronze
No. 11 and later with Low Moor bar, No. 57.

In comparing this standard, a method was employed very similar to that
used in marking it. The bar, properly supported, was placed upon a box
that rested upon rolls, and on this same box was placed the government
standard with which the Brown & Sharpe standard was to be compared.
The standard was placed in position under the microscope, and after being
properly set to the standard, the bar to be measured was placed under the
microscope, and by the micrometer screw of the microscope the variation
was measured. Three comparisons were made by each of the attendants on
each end before determining the reading of the microscope, and after such
comparisons and many repetitions of it, the value of the standard No. 2
was found to be 36.00061 inches for the yard, and 1.0000147 meter for the
meter.

After this work had been done, Mr. Beale prepared a second standard
which he called No. 3, and after examining, as shown above, the error was
found to be 0.00002 inch for the yard, and 0.000005 meter for the meter.
Observing these variations as compared with the standards originally
made, we find they are very close, and it is doubtful if many repeated
trials would furnish more accurate work, when we remember that out of
forty original standards made, but two are correct at 62 degrees
Fahrenheit.

After establishing a yard, the problem of obtaining an inch comes
next, and this was made by subdividing the yard into two equal parts,
these into three, and the three further subdivided into six parts. It
should be particularly noted that no mention has been made of a standard
inch, as there is none, the standard yard only existing, the subdivision
of which falls upon those undertaking standard work. There is a
remarkable agreement between at least three leading gage makers of this
country and abroad, and each came to the result by its own method of
subdividing the standard yard.

Kinds of Measurements and Measuring Tools

The measurements in the shop may, in general, be divided into
measurements of length and measurements of angles. The length
measurements in turn may be divided into line measurements and end
measurements, the former being made by placing a rule or similar
instrument against the object being measured, and comparing its length
with the graduations on the measuring instruments; the latter are made by
comparing the object being measured with the measuring instrument, by
bringing the object measured into actual contact with the measuring
surfaces of the instrument. Examples of line measurements are the
ordinary measurements made with the machinist’s rule, and examples of end
measurement are those made by the micrometer, measuring machines, and
snap gages. Angular measurements can also be divided into two classes;
those measured directly by graduations on the instrument, and those
measured by comparison with a given angle of the instrument.

Measuring instruments may also be divided into two classes, according
to whether they actually are used for measuring, or whether they are
principally used for comparing objects with one another. According to
this classification all kinds of rules and protractors belong to the
first class, whereas all gages belong to the second class. The ordinary
instruments for length measurements, the regular machinists’ rule, the
caliper square, and the ordinary micrometer caliper, are too well known
to require any additional explanation. The same is true of the regular
bevel protractor for measuring angles. We shall therefore in the
following chapters deal principally with special measuring tools, and
with such methods in the use of tools which are likely to suggest
improvements, or otherwise be valuable to the user and maker of measuring
tools.

CHAPTER II

CALIPERS, DIVIDERS, AND SURFACE GAGES

In the present chapter we shall deal with the simpler forms of tools
used for measuring, such as ordinary calipers, and their use; surface
gages; special attachments for scales and squares, facilitating accurate
measuring; and vernier and beam calipers. The descriptions of the tools
and methods referred to have appeared in Machinery from time to time. The names of the persons
who originally contributed these descriptions have been stated in notes
at the foot of the pages, together with the month and year when their
contribution appeared.

Setting Inside Calipers

Figs. 2 and 3Fig. 4

Setting Inside Calipers

It is customary with most machinists, when setting inside calipers to
a scale, to place one end of the scale squarely against the face of some
true surface, and then, placing one leg of the caliper against the same
surface, to set the other leg to the required measurement on the scale.
For this purpose the faceplate of the lathe is frequently used on account
of its being close at hand for the latheman. The sides of the jaws of a
vise or almost anything located where the light is sufficient to read the
markings on the scale are frequently used.

The disadvantages of this method are, first, that a rough or untrue
object is often chosen, particularly if it happens to be in a better
light than a smooth and true one, and, second, that it is very hard to
hold the scale squarely against an object. It is easy enough to hold it
squarely crosswise, but it is not so easy a matter to keep it square
edgewise. As can be readily seen, this makes quite a difference with the
reading of the calipers, particularly if the scale is a thick one.

Figs. 2 and 3 show this effect exaggerated. B is the block
against which the scale abuts. The dotted line indicates where the
caliper leg should rest, but cannot do so, unless the scale is held
perfectly square with the block. Fig. 4 shows a method of setting the
calipers by using a small square to abut the scale and to afford a
surface against which to place the leg of the caliper. The scale, lying
flat on the blade of the square, is always sure to be square edgewise,
and is easily held squarely against the stock of the square as shown.
This method has also the advantage of being portable, and can be taken to
the window or to any place where the light is satisfactory. When using a
long scale, the free end may be held against the body to assist in
holding it in place.^[2]

Shoulder Calipers

Fig. 5. Shoulder Calipers

In Fig. 5 are shown a pair of calipers which are very handy in
measuring work from shoulder to shoulder or from a shoulder to the end of
the piece of work. For this purpose they are much handier, and more
accurate, than the ordinary “hermaphrodites.” The legs are bent at
AA so as to lie flat and thus bring the point of the long leg
directly behind the short one which “nests” into it, as at B, so
that the calipers may be used for short measurements as well as for long
ones.

Double-jointed Calipers to Fold in Tool Box

In Fig. 6 are illustrated a pair of large calipers that can be folded
up and put in a machinist’s ordinary size tool chest. The usual large
caliper supplied by the average machine shop is so cumbersome and heavy
that this one was designed to fill its place. It can be carried in the
chest when the usual style of large caliper cannot. It is a very light
and compact tool. It is a 26-inch caliper, and will caliper up to 34
inches diameter. The top sections are made in four pieces, and the point
ends fit between the top half like the blade of a knife, as shown in the
engraving. Each side of the upper or top section is made of saw steel
1/16 inch thick, and the lower part or point of steel ⅛ inch
thick. The double section makes the tool very stiff and light.

The point section has a tongue A, extending between the double
section, which is engaged by a sliding stud and thumb nut. The stud is a
nice sliding fit in the slot, and the thumb nut clamps it firmly in place
when in use. B, in the figure, shows the construction of the thumb
nut. C is a sheet copper liner put between the washers at
A. The dotted lines in the engraving show the points folded back
to close up. The large joint washers are 1¾ inch diameter, and a
⅝-inch pin with a ⅜-inch hexagon head screw tightens it up.
The forward joints are the same style, but smaller. The main joint has
two 1¾-inch brass distance pieces or washers between the two main
washers. The top section is 12½ inches between centers, and the point
sections 15 inches from center to point. Closed up, the calipers measure
16 inches over-all.

Fig. 6. Large Double-jointed Calipers

Kinks in Inside Calipering

Close measurements may be made by filing two notches in each leg of an
inside caliper so as to leave a rounded projection between, as shown at
E, Fig. 7. Then, with an outside caliper, D, the setting of
the inside caliper, B, is taken from the rounded points. The
inside caliper can be reset very accurately after removal by this method.
A still better way is to have two short pins, CC′ set in the sides of the inside caliper
legs, but this is not readily done as a makeshift. To measure the inside
diameter of a bore having a shoulder like the piece H, the inside
caliper F may also be set as usual and then a line marked with a
sharp scriber on one leg, by drawing it along the side G. Then the
legs are closed to remove the caliper, and are reset to the scribed line.
Of course, this method is not as accurate as the previous one, and can be
used only for approximate measurements.

Fig. 7. Methods of Inside Calipering

To get the thickness of a wall beyond a shoulder, as at K, Fig.
7, set the caliper so that the legs will pass over the shoulder freely,
and with a scale measure the distance between the outside leg and the
outside of the piece. Then remove the caliper and measure the distance
between the caliper points. The difference between these two distances
will be the thickness M.

Inside Calipers for Close Spaces

In Fig. 8 are shown a pair of inside calipers which are bent so as to
be well adapted for calipering distances difficult of access, such as the
keyway in a shaft and hub which does not extend beyond the hub, as
indicated. With the ordinary inside calipers, having straight legs, and
which are commonly used for inside work, it is generally impossible to
get the exact size, as the end which is held in the hand comes in contact
with the shaft before both points come into the same vertical plane. The
engraving plainly shows how calipers for this purpose are made, and how
used. Any mechanic can easily bend a common pair to about the shape shown
to accommodate this class of work.^[3]

Fig. 8. Inside Calipers for Close Spaces

Surface Gage with Two Pointers

Figs. 9 and 10 show a special surface gage, and illustrate an original
idea which has been found to be a great saver of time and of milling
cutters. It can also be used on the planer or shaper. By its use the
operator can raise the milling machine table to the right height without
testing the cut two or three times, and eliminate the danger of taking a
cut that is liable to break the cutter. This tool is especially valuable
on castings, as raising the table and allowing the cutter to revolve in
the gritty surface while finding the lowest spot is very disastrous to
the cutting edges.

Figs. 9 and 10. Surface Gage with Two Pointers

To use this surface gage, the pointer marked C in Fig. 9 is set
to the lowest spot in the casting, and then the pointer B is set
from it with perhaps 1/32 inch between the points for a cut sufficient to
clean up the surface. Pointer C is then folded up as shown at
C′ in Fig. 10, and the table is
raised until the pointer B will just touch the under side of the
cutter as shown at B′ in Fig. 10. In
this way the table is quickly adjusted to a cut that will clean the
casting or other piece being machined, and with no cutting or trying
whatever.^[4]

To Adjust the Needle of a Surface Gage

Fig. 11. Method of Adjusting the Needle of a Surface Gage

Fig. 12. Scale Attachment for the Square

Fig. 11 illustrates a method of adjusting the needle of a surface
gage. To set the gage 3¾ inches from the table, get somewhere within ¼
inch of the mark on the square. With the thumb and forefinger on hook
A, turn the needle till it reaches the point desired. By turning
the needle, it will travel in a circular path, on account of the bend
near the point, and thus reach the desired setting.

Scale Attachment for the Square

Fig. 12 shows a device for attaching a scale to a square. This
combination makes a very convenient tool to use when setting up work for
keyseating, as is illustrated in the engraving, in which S is the
shaft to be splined and C the milling cutter. It is also a very
handy tool for truing up work on the boring mill or lathe. At the upper
left-hand corner, is shown the construction of the parts, which are made
of dimensions to suit the size of the scale and the square. For the
combination to be successful, it is essential that the blade of the
square is the same thickness as the scale.^[5]

Attachment for Machinist’s Scale

Fig. 13. Convenient Attachment for Machinist’s Scale

Fig. 13 shows a very convenient appliance. It will be found very
useful in the machine shop for setting inside calipers to any desired
size. The gage is clamped over the rule wherever desired, and one leg of
the calipers set against the gage, the other leg being brought flush with
the end of the scale.^[6]

Setting Dividers Accurately

To set dividers accurately, take a 1-inch micrometer and cut a line
entirely around the thimble as at A, Fig. 14, and then, with the
instrument set at zero, make a punch mark B exactly one inch from
the line on the thimble. If less than one inch is wanted, open out the
micrometer and set the dividers to the dot and line so as to give one
inch more than the distance wanted. Now with the dividers make two marks
across a line, as at a and b, Fig. 14, and then set the
dividers to one inch and mark another line as at c. The distance
from c to b is the amount desired, and the dividers can be
set to it. Great care must, of course, be exercised, if accurate results
are required.

Fig. 14. Method of Setting Dividers Accurately

Combination Caliper and Divider

The combination caliper and divider shown in Fig. 15 is one that is
not manufactured by any of the various tool companies. It is, however,
one of the handiest tools that can be in a machinist’s kit, as it lends
itself to so many varied uses, and often is capable of being used where
only a special tool can be employed. The illustration suggests its
usefulness. The tool can be used as an outside caliper, as an inside
caliper, and as a divider. The common form of this tool has generally
only one toe on the caliper legs, but the double toes save the reversal
of the points when changing from outside to inside work. The divider
points may be set at an angle, which permits of stepping off readily
around the outside of a shaft at angular distances, where the ordinary
dividers are useless. A number of other uses could be mentioned, but any
intelligent mechanic can readily suggest them for himself.

Fig. 15. Combination Caliper and Divider

Attachment for Vernier Calipers

While vernier and slide calipers are very handy shop tools, their
usefulness is much more limited than it ought to be for such expensive
instruments. In order to increase the usefulness of these tools, the
attachments shown in Fig. 16 may be made. In the upper left-hand part of
the engraving the details of a useful addition to the caliper are shown.
A is made of machine steel, while the tongue B is of tool
steel, hardened and ground and lapped to a thickness of 0.150 inch, the
top and bottom being absolutely parallel. This tongue is secured to
A by the two rivets CC. The thumb-screw D is used
for fastening the attachment to the sliding jaw of the vernier or slide
caliper. In the upper part of the engraving is shown the base, which is
of machine steel, with the slot F milled for the reception of the
fixed jaw of the caliper. The set-screws GGG are put in at a
slight angle so that the caliper will be held firmly and squarely in this
base. In the figure to the left these pieces are shown in the position
for forming a height gage, for which purpose the attachment is most
commonly used. As a test of the accuracy of its construction when the
attachment is placed in this position, the tongue B should make a
perfect joint with the fixed jaw of the caliper, and the vernier should
give a reading of exactly 0.150. When it is desirable that the tongue
B should overhang, the base E is pushed back even with the
stationary jaw, as shown in the engraving to the right. In this position
it is used for laying out and testing bushings in jigs, etc. The
illustration shows the tool in use for this purpose, K being the
jig to be tested. All measurements are from the center line upon which
the bushing No. 1 is placed. Taking this as a starting point we find the
caliper to read 1 inch. Bushing No. 2, which is undergoing the test,
should be ⅝ inch from this center line. It has a ¼-inch hole, and
we therefore insert a plug of this diameter. Now adjust the tongue of the
caliper to the bottom of this plug (as shown in the engraving) and the
vernier should read 1.625 minus one-half the diameter of the plug, or
1.500, and any variation from this will show the error of the jig. In
this case the top surface of B was used and no allowance had to be
made for its thickness. In case the bottom surface is used, 0.150 must be
deducted from the reading of the caliper.

Fig. 16. Attachment for Vernier Calipers

It is very easy to make a mistake in setting a bushing, and such a
mistake is equally hard to detect unless some such means of measuring as
this is at hand. It often happens that jigs and fixtures are put into use
containing such errors, and the trouble is not discovered until many
dollars’ worth of work has been finished and found worthless. The
illustration shows but one of the many uses to which this attachment may
be applied. The figures given on the details are correct for making an
attachment to be used upon the Brown & Sharpe vernier caliper, but
for other calipers they would, of course, have to be altered to suit.^[7]

Improved Micrometer Beam Caliper

Fig. 17. Improved Micrometer Beam Caliper

In a beam caliper having a sliding micrometer jaw with or without a
separate clamping slide, it is necessary to have the beam divided into
unit spaces, at which the jaw or slide may be accurately fixed, the
micrometer screw then being used to cover the distance between the
divisions; but it is difficult to construct a beam caliper of this type
with holes for a taper setting pin, at exactly equal distances apart;
consequently a plan that is generally followed in making such tools is to
provide as many holes through the slide and beam as there are inch
divisions, each hole being drilled and reamed through both the slide and
beam at once. If it were attempted to drill the holes through the beam at
exactly one inch apart, having only one hole in the clamping head and
using it as a jig for the purpose, it would be found very difficult, if
not impossible, to get the holes all of one size and exactly one inch
apart. The design of the micrometer beam caliper shown in Fig. 17, which
has been patented by Mr. Frank Spalding, Providence, Rhode Island, is
such, however, that it is not necessary to drill more than one hole
through the clamping slide. The beam F is grooved longitudinally,
and in the groove are fitted hardened steel adjusting blocks in which a
taper hole D is accurately finished. Between the blocks are
filling pieces G, which are brazed or otherwise fastened in the
groove. Holes are drilled, tapped, and countersunk between the blocks and
the filling pieces G, in which are fitted taper head screws
EE₁. The construction is thus obviously such that the
blocks may be shifted longitudinally by loosening one screw and
tightening the other. In constructing the caliper, the holes through the
beam are drilled as accurately as possible, one inch apart, and centered
in the longitudinal groove, but are made larger than the holes in the
blocks, so as to provide for slight adjustment.

Large Beam Caliper

Fig. 18. Large Beam Caliper

Fig. 18 shows a large beam caliper designed for machinists and
patternmakers. It consists of a beam MN and the legs R and
S, made of cherry wood to the dimensions indicated. The legs are
secured in position on the beam by means of the thumb screws A,
which jam against the gibs C at the points of the screws. The gibs
have holes countersunk for the screws to enter, to hold them
approximately in place, and the nuts B are of brass, fitted into
the filling pieces P that keep them from turning. The filling
pieces are riveted to the legs by means of cherry dowels D. One
leg S is provided with a fine adjustment consisting of flexible
steel spring H, ending in a point which is adjusted by the thumb
screw E. This screw is locked in adjustment by the check nut
G bearing against the brass nut F, which is inserted in the
leg as shown.^[8]

CHAPTER III

MICROMETER MEASURING INSTRUMENTS

Of all measuring instruments used in the shop intended for accurate
measurements, those working on the principle of the ordinary micrometer
calipers are the most common. In the present chapter we shall describe
and illustrate a number of different designs of these tools, intended to
be used for various purposes. The instruments shown in Figs. 19 to 23
were built, in leisure hours, by Mr. A. L. Monrad, of East Hartford,
Conn.

Micrometer for Snap Gages

Fig. 19. Micrometer for Snap Gages

Fig. 19 shows a form of micrometer that has proved very handy for
measuring snap gages, and thicknesses, and can also be used as a small
height gage to measure the distance from a shoulder to the base, as shown
in Fig. 20. In measuring snap gages or thicknesses, the outside and
inside of the measuring disks are used, respectively. This instrument may
also come in very handy when setting tools on the planer or shaper. As
will be seen in the engraving, there are two sets of graduations on the
sleeve A, thus enabling the operator to tell at a glance what
measurement is obtained from the outside or the inside of the measuring
disks. Each of the disks is 0.100 inch thick, so that the range of the
micrometer is 0.800 and 1.000 inch for the outside and inside,
respectively. The details of the instrument are as follows:

The sleeve A is composed of the inside measuring disk, the
graduated sleeve, and the micrometer nut combined. On the disk are two
projections KK, which are knurled, thus providing a grip when
operating the tool. The sleeve is threaded on the inside of one end,
which acts as a micrometer nut, and the outside of this same end is
threaded to receive the adjusting nut D. The sleeve has two slots,
each placed 90 degrees from the graduations, and these provide for
compensation for wear. The disk part is hardened by heating in a lead
bath, and is finished by grinding and lapping. The barrel B is the
same as a regular micrometer barrel, and is graduated with 25 divisions.
Spindle E consists of the outside disk and the micrometer screw,
and the barrel B fits on its end, which is tapped out to receive
the speeder C, which serves to hold the barrel in position. The
thread is ¼ inch, 40 pitch, and the disk and unthreaded parts are
hardened, ground and lapped. To adjust this, instrument, loosen the
speeder C and turn the barrel until the proper adjustment is
obtained. Then lock the barrel by tightening the speeder again.^[9]

Fig. 20. Micrometer in Fig. 19 used as Height Gage

Micrometer Caliper Square

Fig. 21 shows an assembled view and the details of a micrometer
caliper square which, if accurately made, is equal and often preferable
to the vernier caliper now so generally used. One of its advantages over
the vernier is that when the measurement is taken, it can be readily
discerned without straining the eyes, and this instrument is as easy to
manipulate as the regular micrometer.

In the details, part A, which is the main body of the
instrument, is made of tool steel, the forward or jaw end being solid
with the body. This end is hardened, and the jaw ground and lapped. The
body is bored out and two flats milled on the outside, which lighten it
up and make it neat in appearance. The jaw end is counterbored out with a
45-degree counterbore to form a bearing for the forward end of the
micrometer screw. A slot, ⅛ inch in width, extends from the fixed
jaw to the other end, and in this slides the movable jaw C. There
are 44 divisions along the side of this slot, each division being 0.050
inch apart, giving the tool a range of 2.000 inches for outside and 2.200
inches for inside measurements. The screw B is the most essential
part of this tool, its construction requiring great accuracy. Its
diameter is ⅜ inch and it is cut with 20 threads per inch. On its
forward end fits the cone F, which is hardened and ground, the
round part acting as the forward bearing of the screw and fitting in the
45-degree counterbored hole in the body A. On its other end fits
the graduated barrel D and also the speeder G.

Fig. 21. Micrometer Caliper Square

The barrel is graduated in fifty divisions, each division equaling
0.001 inch. On the inside of the barrel is a 45-degree bearing which
rides on the cone M, the cone being held stationary on the end of
the body. Thus it will be seen that both front and back ends of the
micrometer screw are carried in cone bearings, which give a very small
point of contact, thereby causing but little friction and preventing any
danger of gumming up so as to run hard. The sliding jaw C is made
of tool steel, hardened, ground and lapped, and combined with it is the
micrometer nut which is drawn to a spring temper. This nut is split and
adjusted by two screws to compensate for wear. On this jaw are the two
zero marks that tell at a glance the outside or inside measurements
taken. The screw and washer, marked H and I, go onto the
end of the micrometer screw and take up the end play. To make a neat
appearance, the cap E is placed in the forward counterbored hole,
being held in place by a tight fit. The adjustment of the tool is
accomplished by loosening the speeder G and turning the barrel on
the screw; when the adjustment is made, the speeder is again tightened
down and the barrel locked.^[10]

Micrometer Depth Gage

The depth gage, shown in Fig. 22, has a ½-inch movement of the rod,
and may be used with rods of any desired length. These have small
45-degree-on-a-side grooves cut into them at intervals of ½ inch. A small
spiral spring, marked I, gives the rod a constant downward
pressure, so that, when taking a measurement, the base of the tool is
placed on the piece of work, and the rod always finds the bottom of the
hole; then, by tightening the knurled screw F the rod is clamped
in position and the tool may be picked up and its measurement read from
the dial. The graduations on this instrument are similar to those of the
vernier caliper, only they are much plainer, as a half-inch movement of
the rod turns the dial one complete revolution. The figures on the dial
denote tenths of an inch, and those on the body of the tool thousandths;
each graduation on the dial is therefore equal to 0.010, so that to show
the depth of a hole to be 0.373 the dial would be revolved around so that
the seventh division beyond the 3 mark would be near to 0, and then by
looking from the 0 mark toward the left, the third graduation on the body
and one on the dial would be in line, thus denoting 0.373.

Fig. 22. Micrometer Depth Gage

The most essential part of this tool is the threaded screw B,
which acts as a rack, and the worm-wheel, solid with the dial C.
The upper end of the screw forms a split chuck which grips the measuring
rods, while the part marked R is flatted off, and against this
portion bears a threaded sleeve G, which acts as a key to keep the
screw in position. This sleeve is threaded, both inside and outside, and
screws into the body of the tool, while the binding screw F fits
into it and binds against a small piece of copper, marked H, which
in turn holds the screw in position. The thread on B is 0.245 inch
in diameter and is cut with 40 threads per inch. The worm-wheel which
meshes into this screw is solid with the dial, as shown at C. It
is 0.18 inch in diameter, and requires great accuracy in cutting; it is
not hobbed, but the teeth, of which there are twenty, are milled with a
circular cutter of the same diameter as the screw B plus 0.002
inch. The little studs, marked EE, on the dial and on the body
K, hold the coiled spring in position. Very great accuracy must be
attained when locating the holes in K that are to receive the
screw and dial B and C. The screw marked J fits into
the dial, where it serves as a bearing and also holds the dial in
position. The knurled cap D tightens the split chuck in order to
hold the measuring rod firmly.^[11]

Indicator for Accuracy of Lead-screws

Fig. 23. Indicator for Accuracy of Lead-screws

All of the tools that have been described require an accurately cut
screw, and, as very few lathes are capable of producing this, it may be
well to illustrate an indicator for testing the accuracy of the
lead-screw, and to explain the method by which it is used. This
instrument is shown in Fig. 23, where it is applied to a test screw
K. It consists of a body A on one end of which is a
projection L serving as the upper bearing for the pivoted lever
D. This lever swings about a small steel pivot which can be
adjusted by the screw E. The rear end of the lever is forked, and
between the prongs is passed a thread making a double turn about the
pivot F that carries the pointer J. Any movement of this
lever will, therefore, cause this pointer to revolve about the dial
C. This dial has 20 divisions, each indicating one-half thousandth
of an inch movement of the front end of the lever, so that a total
revolution of the pointer about the dial would indicate a movement of the
front end of the lever of 0.020 inch. The screws I serve to hold
the dial in place on the body of the indicator, while the spring M
keeps the pointer normally at the zero mark. The indicator is held in the
toolpost by the arm G, which can be set at any angle and firmly
clamped by the screw H.

To use the indicator, remove the screw from a micrometer which is
known to be accurate, and, with the aid of a brass bushing, chuck it in
the lathe so that the thread end will project. Now gear the lathe to cut
40 threads per inch and apply the indicator. When the lathe is started,
the point of the indicator follows along in the thread of the micrometer
screw, and any variation in the lead will be noted by a movement of the
pointer over the dial. If, on the other hand, no movement takes place, it
is an indication that the pitch of the lead-screw is correct.^[12]

Micrometer Attachment for Reading Ten-thousandths of an Inch

Fig. 24. Micrometer with Attachment for Reading Ten-thousandths of an Inch

Fig. 24 shows an attachment for micrometers designed and made for
readings in tenths of thousandths of an inch. With very little fitting it
is interchangeable for 1-, 2-, or 3-inch B. & S. micrometers. The
idea is simple, as can be seen by the illustration. The diameter of the
thimble is increased 3 to 1 by a disk which is graduated with 250 lines
instead of 25, making each line represent 0.0001 inch instead of 0.001
inch. A piece of steel is then turned up and bored and cut away so as to
form the index blade and a shell to clasp the micrometer frame, the whole
thing being made in one piece. The thimble disk being just a good
wringing fit, it can be easily adjusted 0 to 0. The attachment can be
removed when fine measuring is not required.^[13]

Special Micrometer for Large Dimensions

Fig. 25 shows a 6-inch micrometer caliper designed for measuring from
0 to 6 inches by half-thousandths. The sliding micrometer head travels on
a cylinder barrel through which a hole is accurately bored to suit three
plugs, one, two, and three inches long, as shown in the engraving. These
plugs serve to locate the traveling head at fixed distances one inch
apart. The micrometer screw itself has a travel of one inch, like any
standard micrometer. A locknut is used to hold the screw in any desired
position. A thumb screw at the end of the barrel bears against the end
plug, and zero marks are provided to bring the screw against the plug
with the same degree of pressure at each setting. When the head is
clamped by means of the locking nut, it is as rigid as though it were
solid with the barrel, and the faces of the measuring points are thus
always parallel.

Fig. 25. Special Micrometer for Large Dimensions

Combination Micrometer

Fig. 26. Combined One- and Two-inch Micrometer

A combined one- and two-inch micrometer is shown in Fig. 26. One side
records measurements up to one inch, and the other side up to two inches.
A single knurled sleeve or nut serves to move the double-ended measuring
piece one way or the other as desired, this piece having a travel of one
inch. The spindle is non-rotating, so that the faces of the screw and
anvil are always parallel. A locking device holds the screw in any
position. This tool is convenient for use both in measuring and as a
gage, since it can be conveniently held by the finger ring appearing at
the back.

Micrometer Stop for the Lathe

Most micrometer lathe stops are limited in their use to work where
only a stationary height is required. It is, however, often necessary to
use the stop at different heights, to accommodate different lathes; then
again, we wish to use it on the right-hand side as well as the left. The
form of holder shown in Fig. 27 can be used either right or left, and for
various heights, and, by simply taking out the screw A, the
micrometer may be removed and used in any other form of holder
desired.

Fig. 27. Micrometer Stop for the Lathe

Both an assembled view and details of the holder are shown in the
engraving, so that it can be easily constructed by any one desiring to do
so. The micrometer and barrel may be procured from any of the
manufacturers of measuring instruments. The swivel C is bored out
so that the axis of the micrometer screw will be parallel to the body of
the holder when it is in place. The swivel is made of tool steel and is
fastened to the holder by the screw A. It is hardened and lapped
to a true bearing surface on the sides and bottom, and so adjusted that
it will turn to either side and remain in the desired position without
moving the screw. The holder B is milled through its entire length
with a 90-degree cutter so that it will fit along the ways of the lathe,
and the bottom is lapped to a true surface. For a neat appearance, the
tool should be color hardened. On top the holder is spotted or
countersunk with a drill to form a recess for the C-clamp. A knurled ring
D is driven onto the micrometer sleeve so that it can be turned
around to bring the graduations uppermost when the position of the barrel
is changed.^[14]

Micrometer Surface and Height Gage

Fig. 28. Micrometer Surface and Height Gage

Fig. 28 shows a form of surface gage that has proved very handy, and
which can be used also as a height gage for measuring distances from
shoulders to the base. If accurately made it is equal, and often
preferable, to the vernier or slide caliper now so generally used with an
attachment to the sliding jaw. One of its advantages over the vernier is
the readiness with which the graduations are discerned, and it is as easy
to manipulate as the ordinary micrometer. The part B, which forms
the main body of the instrument, is made of tool steel, and one end is
fitted into the base where it is held in position by the screw D.
The remainder is milled to a thickness of ⅛ inch and has
graduations of 0.025 inch for a distance of three inches. The screw
A is the most essential part of the tool, and its construction
requires great accuracy. Its diameter is ½ inch, and it is cut with 20
threads per inch. In the upper end of the screw is driven the ball
H for the sake of giving a neat appearance. The top of the thread
is turned off 0.010 inch to allow the scriber F to slide freely on
the screw. The barrel I is used for raising and lowering the
slide, but instead of having the graduations placed directly upon it,
they are made upon the sleeve C, which fits over a shoulder on the
barrel. This allows more easy means of adjustment than would be possible
were the graduations placed on the barrel itself. The sleeve is graduated
with fifty divisions each equaling a movement of the scriber of 0.001
inch. This sleeve may be turned by means of a small spanner wrench so as
to bring the zero line into correct position to compensate for wear. A
knurled locking nut is also provided for holding the scriber in any fixed
position. The scriber itself is hardened and lapped to a finished
surface, the tail end being slotted and provided with two screws to
compensate for wear. On the scriber is placed the zero mark which shows
at a glance the measurement that is being taken. The block K is
three inches in height, and by using this block and placing the gage on
its top, the range of the gage is increased to six inches. The screw
E is used for fastening the gage to the top of the block. The
center of the block is drilled out and slots cut through the sides in
order to make it light and neat in appearance.^[15]

Micrometer of from One- to Five-inch Capacity

Fig. 29. Micrometer of from One- to Five-inch Capacity

Fig. 29 shows a very simple and light five-inch micrometer that can be
quickly set to exact position from one to five inches. The round beam is
graduated by a series of angular grooves, 1 inch apart, which are of such
a form and depth that the clamping fingers at the end of part A
spring in, allowing one inch adjustment of the beam to be quickly and
positively made. The sleeve K is of tool steel, being counterbored
from the forward end for all but one-half inch of its length. For this
half inch it is threaded on the inside and acts as a micrometer nut. The
outside of the same end is threaded to receive the adjusting nut
F, and two slots are cut in the sleeve, at 90 degrees with the
graduations. These slots, by a movement of the nut F, provide a
means for compensating for wear. The bushing E is hardened and
lapped, and fitted tightly in the forward counterbore of this sleeve,
where it acts as a guide for the front end of the micrometer screw. The
barrel J is the same as that of a regular micrometer, and is
graduated in 0.025 inch divisions.

The most essential part of the tool is the threaded screw I,
over the end of which fits the barrel J. The end is tapped out to
receive the speeder H, which serves to hold the barrel in
position. The thread is 5/16 inch in diameter, with 40 threads per inch,
while the unthreaded part is hardened, ground and lapped. To adjust the
instrument, loosen the speeder H and turn the barrel until the
proper adjustment is obtained; lock the barrel by again tightening the
speeder. The beam C has a ¼-inch hole drilled throughout its
entire length in order to make it light. Small 90-degree grooves are cut
into it at intervals of 1 inch, and a ⅛-inch slot is milled
through one side to within 1¼ inch of the forward end. The back end of
part A forms a spring-tempered split chuck, which grips the beam
and holds A in position, while the exterior is threaded to receive
the knurled cap B by which the chuck is tightened firmly to the
beam. From the front end, toward the split chuck, the body is
counterbored ⅝ inch and the bushing D driven in tight. This
bushing has a key G fitted into it, which slides in the slot of
the beam and prevents the arm from turning. The projecting arm is bored
and tapped to receive the sleeve K. This gage must be carefully
and accurately made to be of value.^[16]

Inside Micrometer for Setting Calipers

Fig. 30. Method of Setting Calipers from Inside Micrometers

Fig. 30 shows an application of inside micrometers which is very
handy. The hole for the scriber in the scriber clamp of a surface gage is
reamed out to fit the rods used with inside micrometers. This forms a
convenient holder for the micrometer when used for setting outside
calipers to it. The calipers can be set easily and accurately at the same
time, and where extreme accuracy is not necessary this arrangement is
more handy than that of using large-sized micrometers.

With care and practice an accuracy of within one-quarter of 0.001 inch
is obtainable in this way. Mistakes, in fact, are more easily guarded
against than is the case when using the micrometers directly.

Micrometer Frame

Fig. 31. Useful and Handy Micrometer Frame

Fig. 31 shows a micrometer frame used some years ago at the
Westinghouse works. The frame is an aluminum casting, and the anvil is
simply a tool-steel pin, which fits well in the hole into which it is
inserted, and can be clamped anywhere within the limits of its length.
The micrometer end of the frame is supplied with an inside micrometer
head. The tool is adjusted to a gage, either to a standard pin gage, or
to an inside micrometer gage. The capacities of three of these
micrometers in a set may be from about 3½ to 7 inches, 6 to 11 inches,
and 10 to 15 inches. When the head is turned outward, as shown in the
lower view in the cut, the tool is very handy around a horizontal boring
machine where a pin gage cannot be used without removing the boring
bar.

Micrometer Stop for the Lathe

Fig. 32. Micrometer Stop for the Lathe

The simple micrometer stop shown in Fig. 32 is used on the engine
lathe for obtaining accurate movements of the lathe carriage. It consists
of a micrometer head, which can be purchased from any micrometer
manufacturer, and a machine steel body which is bored to fit the
micrometer head. This tool is clamped on the front way of the lathe bed,
and when the jaw of the micrometer is against the lathe carriage, it can
easily be adjusted to a thousandth of an inch. Of course, care should be
taken not to bump the carriage against the micrometer.^[17]

Use of Micrometer for Internal Thread Cutting

Fig. 33. Method of using Micrometer for Internal Thread Cutting

Fig. 33 illustrates a means of determining the size of internally
threaded work. The work shown is intended for a lathe chuck. The outside
diameter of the hub on the work is turned to the same size as the hubs on
small faceplates which are furnished with all new lathes. The threaded
size is then taken and transferred with a micrometer, over the anvil of
which is fitted a 60-degree point as shown enlarged at A. In
connection with a graduated cross-feed screw this greatly facilitates the
work over the usual cut-and-try method.^[18]

Inside Micrometer

The inside micrometer shown in sections in Figs. 34 and 35 is adapted
to measuring, by use of extension rods, from 2 inches up to any size of
hole, and has one inch adjustment of the measuring screw.

Figs. 34 and 35. Section of Inside Micrometer

Referring to the section shown in Fig. 35, the measuring screw
S is secured to the thimble B with the screw D, the
head of which is hardened and forms the anvil. By loosening this screw
D, the thimble can be rotated to compensate for wear. The wear of
the measuring screw and nut is taken up by screwing the bushing A
into the frame with the wrench shown in Fig. 37. This bushing is split in
three sections for about two-thirds of its length on the threaded end.
The three small lugs on the wrench fit into these slots. The handle end
of the wrench is a screw driver which is used for manipulating the set
screw C. The bushing is made an easy fit in the frame on its plain
end and tapered, as shown, on its outside threaded part. This thread
being the same pitch as the measuring screw, adjustment for wear does not
affect the reading of the micrometer. This manner of adjustment brings
the nut squarely down on the measuring screw for its whole length,
presenting the same amount of wearing surface after adjustment as when
new.

Fig. 36. Handle for Inside Micrometer

Fig. 37. Wrench used with Inside Micrometer

The point F, which is hardened on its outer end, screws into
the frame, and is secured by the taper-headed screw O, which
screws into and expands the split and threaded end of the point F.
The handle, Fig. 36, clamps over the knurled part of the frame for use in
small, deep holes. The rods, six in number, running from 1 to 6 inches
inclusive, are made by screwing a sleeve onto a rod with a hardened point
and locking it with a taper-headed screw on its threaded and split end,
the same as in the point F. The extension pieces, Fig. 38, are
adjustable, on their socketed ends, in the same way, and run in lengths
of 6, 12, 18 inches, etc.^[19]

Fig. 38. Adjustable Extension Pieces for Inside Micrometer

Direct Fractional-reading Micrometer

Fig. 39. Direct Fractional-reading Micrometer

The direct fractional-reading micrometer shown in Fig. 39 is the
result of talks with many mechanics in which all agreed that such a
feature added to a micrometer would, by making it both a fractional and
decimal gage, more than double its practical value. While approximate
readings in 64ths, etc., may be obtained by the graduations on the barrel
B as on an ordinary inch scale, the exact readings of 64th, etc.,
may be obtained only by reference to graduations on the movable thimble
A. There are but eight places on A which coincide with the
long graduation line on B when any 64th, 32d, 16th, or 8th is
being measured, and each of these eight places is marked with a line, and
the 64th, 32d, 16th, or 8th for which that line should be used is marked
thereon. (See a and b, Fig. 40.) The line a would be
used for 3/32, 7/32, 11/32, etc., and the line b for 1/64, 9/64,
17/64, etc. Now suppose we wish to accurately measure 15/32 inch. We
first roughly read it off the inch scale on sleeve B by turning
out thimble A. Having secured it closely by drawing edge of
A over that graduation, we find that the line a (Fig. 40)
on the movable thimble very nearly or exactly coincides with the long
graduation line on B. When these lines coincide, we have the exact
measurement of 15/32 inch without reference to how many thousandths may
be contained in the fraction. Thus all through the scale any fraction may
be found instantly. There is no mental arithmetic, use of tables, or
memory work in using the tool. The new graduations are independent of the
old, and may be used equally well with or without them.

Fig. 40. Graduations on the Fractional-reading Micrometer

Micrometers may also be graduated as in Fig. 41. Instead of using the
zero line on A as a base line, a point is taken one-fifth of a
turn around A, and the graduated scale on B is placed to
correspond, as shown in the engraving; also, instead of making lines
a, b, etc., on A, full length, they are made about
half an inch long, and the numerators are entirely omitted and the
denominators placed at the end instead of under the line. To the ordinary
user of the tool, this is all that is necessary for a perfectly clear
reading of the fractions.^[20]

Fig. 41. Another Method of Graduating for Fractional Reading

Sensitive Attachment for Measuring Instruments

No matter how finely and accurately micrometers and verniers may be
made, dependence must in all cases be placed on the sensitiveness of a
man’s hand to obtain the exact dimensions of the piece to be measured. In
order to overcome this difficulty and eliminate the personal equation in
the manufacture of duplicate and interchangeable parts, the sensitive
attachment to the micrometer shown in Fig. 42 may be used, and will be
found of much value.

Fig. 42. Sensitive Micrometer Attachment

The auxiliary barrel A is held to the anvil of the micrometer
by means of a thumb screw B. At the inside end of the barrel is a
secondary anvil C, the base of which bears against the short arm
of the indicating lever D. The action will be clearly seen by
reference to the engraving. The micrometer is so set that when a gage,
G, of exact size, is placed between the measuring points, the long
arm of the indicator stands at the 0 mark. If the pieces being calipered
vary in the least from the standard size it will be readily noted by the
movement of the pointer. Hard rubber shapes turned from rough casting
often vary from 0.003 to 0.005 inch after having passed the inspector’s
test with an ordinary micrometer. With this attachment the inspector’s
helper can detect very minute variations from the limit size. Anything
within the limits of the micrometer can be made to show to the naked eye
variations as small as a ten-thousandth inch.^[21]

Another Sensitive Micrometer Attachment

Fig. 43. Another Sensitive Micrometer Attachment

When testing the diameters of pieces that are handled in great
quantities and are all supposed to be within certain close limits of a
standard dimension, the ordinary micrometer presents the difficulty of
having to be moved for each piece, and small variations in diameters have
to be carefully read off from the graduations on the barrel. Not only
does this take a comparatively long time, but it also easily happens that
the differences from the standard diameter are not carefully noted, and
pieces are liable to pass inspection that would not pass if a convenient
arrangement for reading off the differences were at hand. Fig. 43 shows a
regular Brown & Sharpe micrometer fitted with a sensitive arrangement
for testing and inspecting the diameters of pieces which must be within
certain close limits of variation. The addition to the ordinary
micrometer is all at the anvil end of the instrument. The anvil itself is
loose and consists of a plunger B, held in place by a small pin
A. The pin has freedom to move in a slot in the micrometer body,
as shown in the enlarged view in the cut. A spring C holds the
plunger B up against the work to be measured, and a screw D
is provided for obtaining the proper tension in the spring. The screw and
the spring are contained in an extension E screwed and doweled to
the body of the micrometer. A pointer or indicator is provided which is
pivoted at F and has one extensional arm resting against the pin
A, which is pointed in order to secure a line contact. At the end
of the indicator a small scale is graduated with the zero mark in the
center, and as the indicator swings to one side or the other the
variations in the size of the piece measured are easily determined. A
small spring G is provided for holding the pointer up against the
pin A. The case H simply serves the purpose of protecting
the spring mentioned. As the plunger B takes up more space than
the regular anvil, the readings of the micrometer cannot be direct. The
plunger B can be made of such dimensions, however, that 0.100 inch
deducted from the barrel and thimble reading will give the actual
dimension. Such a deduction is easily done in all cases. In other words,
the reading of the micrometer should be 0.100 when the face of the
measuring screw is in contact with the face of the plunger; the 0.100
inch mark is thus the zero line of this measuring tool.

When desiring to measure a number of pieces, a standard size piece or
gage is placed between the plunger B and the face L of the
micrometer screw, and the instrument is adjusted until the indicator
points exactly to zero on the small scale provided on the body of the
micrometer. After this the micrometer is locked, and the pieces to be
measured are pushed one after another between the face L and the
plunger B, the indications of the pointer M being meanwhile
observed. Whenever the pointer shows too great a difference, the piece,
of course, does not pass inspection. All deviations are easily detected,
and any person of ordinary common sense can be employed for inspecting
the work.

Micrometer Scale

Fig. 44. Micrometer Mounted on Machinist’s Scale

A micrometer, mounted as shown in Fig. 44 is very handy. The
micrometer may be used in combination with a 4-, 6-, 9-, or 12-inch
scale. It can be adjusted on standard plugs, or one can make a set of
gages up to 12 inches, out of 3/16-inch round tool steel wire, and use
these for setting. In mounting the micrometer, before cutting it apart,
mill the shoulders shown at A, and in milling the bottom pieces
B, use a piece of machine steel long enough for both, cutting the
piece in half after milling the slots. In this way one obtains perfect
alignment. In a shop where a set of large micrometers is not kept, this
arrangement is very useful.^[22]

CHAPTER IV

MISCELLANEOUS MEASURING TOOLS AND GAGES

Among the miscellaneous measuring tools and gages dealt with in this
chapter are tools and gages for measuring and comparing tapers,
adjustable gages, radius gages, gages for grinding drills, sensitive
gages, tools for gaging taper threaded holes, contour gages, etc. Of
course, these are offered merely as examples of what can be done in the
line of measuring tools for different purposes, and, while having a
distinct and direct value to the mechanic, they also have a great
indirect value, because they furnish suggestions for the designing and
making of tools for similar purposes.

Tool for Measuring Tapers

Fig. 45. Taper Measuring Tool

Fig. 45 shows a tool which has proved very useful. It is a tool for
measuring tapers on dowel pins, reamers, drill shanks, or anything to be
tapered. Most machinists know that to find the taper of a shank they must
use their calipers for one end and reset them for the other end; or else
caliper two places, say, three inches apart, and if, for instance, the
difference should be 1/16 inch, they must multiply this difference by
four to get the taper per foot. With the tool above mentioned, all this
trouble in calipering and figuring is saved. Simply place the shank or
reamer to be measured between pins A, B, C, and
D, and slide H and K together. Then the taper can be
read at once on the graduated scale at L. The construction of the
tool will be readily understood. The body or base F has a cross
piece supporting the two pins A and B. On this slides piece
K, which has at its right end the graduated segment. The screw
G is fast to piece K, and upon it swivels the pointer
E, which carries the two pins C and D. Thus these
two pins can be brought into contact with a tapered piece of any diameter
within the capacity of the tool, and the swivel screw G allows the
pins to adjust themselves to the taper of the work and the pointer
E to move to the left or right, showing instantly the taper per
foot.

As the pins A and B are 1½ inch apart, which is ⅛
of a foot, and the distance from G to L is 4½ inches, which
is three times longer than the distance between A and B,
the graduations should be 3/64 inch apart, in order to indicate the taper
per foot in eighths of an inch.^[23]

Taper Gage

Fig. 46. Handy Taper Gage

A handy taper gage is shown in Fig. 46. The blades of the gage are
made of tool steel. The edge of the blade A is V-shaped, and the
blade B has a V-groove to correspond. The end of B is
offset so as to make the joint and allow the two blades to be in the same
plane. A strong screw and nut are provided to hold the blades at any
setting. The user of this gage looks under the edge of A, and is
thereby enabled to tell whether the taper coincides with that set by the
gage, and also where a taper piece needs touching up to make it true.^[24]

Test Gage for Maintaining Standard Tapers

Fig. 47. Test Gage for Maintaining Standard Tapers

In steam injector work, accurately ground reamers of unusual tapers
are commonly required, and the gage shown in Fig. 47 was designed to
maintain the prevailing standard. It consists of a graduated bar, 1 inch
square, with the slot F running its entire length. The stationary
head A is secured in position flush with the end of the bar, and
the sliding head B is fitted with a tongue which guides it in the
slot. This head may be secured in any desired position by means of a
knurled thumb nut. The bushings D and D′ are made of tool steel, hardened and
ground to a knife edge on the inside flush with the face. All bushings
are made interchangeable as to outside diameter.

The head B is fitted with an indicating edge E which is
set flush with the knife edge of the bushing. The reading indicates to
0.010 inch the distance the bushings are from each other, and the
difference in their diameter being known, it is easy to compute the
taper. With this gage it is possible to maintain the standard tapers
perfectly correct, each reamer being marked with the reading as shown by
the scale.^[25]

Inside and Outside Adjustable Gages

Fig. 48. Adjustable Gage for Inside and Outside Measurements

Fig. 48 shows an inside and an outside adjustable gage for accurate
work, used in laying out drill jigs, and in setting tools on lathes,
shapers, planers, and milling machines. The outside gage is shown in the
side view and in the sectional end view marked Y. At X in
the same figure is a sectional end view showing how the gage is
constructed for inside work. The top and bottom edges are rounded, so
that the diameters of holes may be easily measured.

The gage consists of a stepped block B, mounted so as to slide
upon the inclined edge of the block C. There are V-ways upon the
upper edge of the latter, and the block B is split and arranged to
clamp over the ways by the screw shown at S. All parts of the gage
are hardened and the faces of the steps marked A, are ground and
finished so that at any position of the slide they are parallel to the
base of the block C. The lower split portion of the block is
spring-tempered to prevent breaking under the action of the screw, and
also to cause it to spring open when loosened. The gage has the advantage
that it can be quickly adjusted to any size within its limits, which does
away with using blocks. In planing a piece to a given thickness, the gage
may be set to that height with great accuracy by means of a micrometer
caliper, and then the planer or shaper tool adjusted down to the gage.
This method does away with the “cut-and-try” process, and will bring the
finishing cut within 0.001 inch of the required size. If the piece being
planed, or the opening to be measured, is larger than the extreme limit
of the gage, parallels may be used. In fitting bushings into bushing
holes, the adjustable gage may be moved out to fit the hole, and then,
when the bushing is finished to the diameter given by the gage, as
determined by a micrometer caliper, a driving fit is ensured.^[26]

Radius Gage

Fig. 49. Radius Gage

Fig. 49 shows a radius gage which has proved to be very handy for all
such work as rounding corners or grinding tools to a given radius. The
blades are of thin steel, and are fastened together at the end by a
rivet, thus forming a tool similar to the familiar screw pitch gage. The
right-hand corner of each blade is rounded off to the given radius, while
the left-hand corner is cut away to the same radius, thus providing an
instrument to be used for either convex or concave surfaces. The radius
to which each blade is shaped is plainly stamped upon the side.^[27]

Gage for Grinding Drills

Fig. 50. Gage for Grinding Drills

Fig. 50 shows a gage for use in grinding drills, which has been found
very handy and accurate. This gage enables either a large or small drill
to lie solidly in the groove provided for it on top of the gage, and the
lips can then be tested for their truth in width, or angle, much easier
and quicker than with the gages in common use without the groove. There
is a line, to set the blade B by, on the stock at an angle of 59
degrees at the top of the graduated blade, and the user can easily make
other lines, if needed for special work. The blade is clamped in position
by the knurled nut N at the back, and can be thus adjusted to any
angle. The stock A is cut away where the blade is pivoted on, so
that one side of the blade comes directly in line with the middle of the
groove.^[28]

Tool for Gaging Taper Threaded Holes

Fig. 51. Tool for Gaging Taper Threaded Holes

The tool shown in Fig. 51 is used for gaging taper threaded holes in
boilers when fitting studs. It is a simple, though very useful and
economical tool, and it will doubtless be appreciated by those having
much work of this kind to do. The hole in which the stud is to be fitted
is calipered by filling the threads of the plug with chalk, and then
screwing the plug in the hole. When the plug is removed the chalk will
show exactly the largest diameter of the hole.^[29]

Contour Gage

Fig. 52. Setting Contour Gage to Turned Sample

Fig. 53. End View of Contour Gage

Figs. 52, 53 and 54 illustrate a special tool which will be found of
great value in certain classes of work. The need of some such device
becomes apparent when patterns and core boxes are required to be
accurately checked with the drawings of brass specialties, in particular.
The tool is applied to the work, and the wires pressed down onto the
contour by using the side of a lead pencil. Of course, patterns parted on
the center could have their halves laid directly on the drawing without
using the contour gage, but some patterns are cored and inseparable. Such
a tool proves a relentless check upon the patternmaker, who, by making
the patterns larger than necessary, can cause a considerable loss in a
business where thousands of casts are made yearly from the same patterns.
As a ready and universal templet it is very useful.^[30]

Fig. 54. Testing Core-box with Gage

Testing a Lead-screw

Fig. 55. Micrometer for Testing Lathe Lead-screw

A reliable way for testing the pitch of a lead-screw, at any position
of its length, is to procure a micrometer screw and barrel complete, such
as can be purchased from any of the manufacturers of accurate measuring
instruments, and bore out a holder so that the axis of the micrometer
screw will be parallel to the holder when the screw is in place, as shown
in Fig. 55. With the lathe geared for any selected pitch, the nut engaged
with the lead-screw, and all backlash of screw, gears, etc., properly
taken up, clamp the micrometer holder to the lathe bed, as shown in Fig.
56, so that the body of the holder is parallel to the carriage. Adjust
the micrometer to one inch when the point of the screw bears against the
carriage and with a surface gage scribe a line on the outer edge of the
faceplate. Now rotate the lathe spindle any number of full revolutions
that are required to cause the carriage to travel over the portion of the
lead-screw that is being tested, bringing the line on the faceplate to
the surface gage point. If the distance traveled by the carriage is not
greater than one inch, the micrometer will indicate the error directly.
For lengths of carriage travel greater than one inch, an end measuring
rod, set to the number of even inches required, can be used between the
micrometer point and lathe carriage. The error in the lead-screw is then
easily determined by the adjustment that may be required to make a
contact for the measuring points between the carriage and the micrometer
screw. The pitch can be tested at as many points as are considered
necessary by using end measuring rods, of lengths selected, set to good
vernier calipers. The style of holder shown can, with the micrometer
screw, be used for numerous other shop tests, and as the screw is only
held by friction caused by the clamping screw, it can easily be removed
and placed in any form of holder that is found necessary.^[31]

Fig. 56. Testing a Lathe Lead-screw

Simple Tool for Measuring Angles

Fig. 57. Special Tool for Measuring Angles

Fig. 57 shows a very simple, but at the same time, a very ingenious
tool for measuring angles. Strictly speaking, the tool is not intended
for measuring angles, but rather for comparing angles of the same size.
The illustration shows so plainly both the construction and the
application of the tool, that an explanation would seem superfluous. It
will be noticed that any angle conceivable can be obtained in an instant,
and the tool can be clamped at this angle by means of screws passing
through the joints between the straight and curved parts of which the
tool consists. Linear measurements can also be taken conveniently, one of
the straight arms of the tool being graduated. As both of the arms which
constitute the actual angle comparator are in the same plane, it is all
the easier to make accurate comparisons. This tool is of German design,
and is manufactured by Carl Mahr, Esslingen a. N.

Bevel Gear-testing Gage

Fig. 58. Sensitive Gear-testing Gage

In Fig. 58 is shown a sensitive gage for inspecting small bevel gears.
The special case shown to which the gage is applied in the engraving is a
small brass miter gear finished on a screw machine, in which case some of
the holes through the gears were not concentric with the beveled face of
the gears, causing the gears to bind when running together in pairs. The
gage shown is quite inexpensive, but it indicates the slightest
inaccuracy.

NOTES