Improvements in Micrometer Calipers.
Year: 1891

page_text: Date of Application, 7th July, 1891-Accepted, 8th Aug., 1891
COMPLETE SPECIFICATION.
Improvements in Micrometer Calipers.
A communication from abroad by JOHN DAVID SLOANE, of St. Paul, in the
County of Ramsey and State of Minnesota, United States of America,
Mechanical Engineer.
I, WILLIAM PHILLIPS THOMPSON, F.C.S., M.I.M.E., of the Agency for Foreign
Patent Solicitors, 6, Lord Street, Liverpool, and 6, Bank Street, Manchester, both
in the County of Lancaster, and 323, High Holborn, in the County of Middlesex,
Civil Engineer, do hereby declare the nature of this invention and in what manner
the same is to be performed, to be particularly described and ascertained in and
by the following statement :-
This invention relates to improvements in micrometer calipers, designed especially
for measuring the thickness of plates of steam boilers, to determine the amount
of erosion. To do this it is necessary to drill through the plate a hole of
sufficient size to admit the calipers or other measuring instrument, the hole being
usually not less than an inch in diameter. This is afterwards closed by means of a
screw plug, but nevertheless weakens the boiler plate. The object of this invention
is to provide an instrument by means of which the required measurement can be
made through a very much smaller hole, usually about an eighth of an inch in
diameter which is no appreciable injury to the plate.
The invention consists in making the calipers with one leg in the form of a hollow
cylinder, and the other as a small rod sliding in the cylinder, each provided with a
caliper point offset from their common axis. The inner leg is normally held
from turning, and with the points in alignment, by means of a feather sliding in
groove in the cylinder, a spring in the cylinder tending to slide the rod
inward and to close the caliper points. The inner leg or rod is thrust outward by
means of a plunger, so as to separate the caliper pointe, and may be pushed outward
far enough to free the feather from the groove and permit the leg to be rotated to
laterally separate the caliper points. The point carried by the inner leg, can be
inserted through a small hole into the interior of the boiler, and then turned back
into alignment with the other point, when the spring closes them together upon the
plate. A suitable scale and indicator are carried by the cylinder and rod, so that
the distance between the points may be determined, and an adjustable stop is also
provided to prevent the points from closer approach, so that, after the instrument
is removed from the boiler, the reading can be taken therefrom.
In the drawings forming part of this Specification :
Figure 1 is a plan view of the instrument,
Figure 2 à partial longitudinal section on line x-x of Figure 4;
Figure 3 a similar section on line y-y of Figure 4 showing a modified
construction, and
Figure 4 an end elevation.
2 represents the fixed caliper leg in form a hollow cylinder, 4 a lateral extension
of the leg carrying the point 6, and 8 a shoulder in alignment with the point 6 at
right angles with the axis of the leg. 10 is the adjustable leg, sliding and turning
in the leg 2, and having the lateral projection or hook 12 carrying the point 13.
14 is a feather upon the leg 10 engaging a groove in the leg 2, and normally holding
the leg from turning and the points in alignment. 16 is a longitudinal slot through
the wall of the leg 2 marked with the graduated scale 18. 20 is a sleeve
surrounding the reduced inner end of the leg 10, having the head 22 fitting within
the leg 2, and provided with the lug 24 projecting through the slot 16, serving as
an indicator for the scale and inscribed with the vernier scalo 25, the sleeve being
held upon the leg 10 by the nut 26 threaded upon the leg. 28 is a spiral spring

page_text: surrounding the leg 10 within the leg or cylinder 2, bearing against the head 22
and the end of the cylinder and tending to force the leg 10 inward to close
the caliper points. 30 is a plunger sliding in the leg 2, having on its outer end the
head 32, and on its inner end the head 34 fitting closely within the barrel of the
leg 2, and provided with points 36 adapted to engage sockets 38 in the nut 26
against which it abuts. 39 is a sleeve fitted upon the plunger having the head 35,
and threaded into the boss 40 of the cap nut 42 which is screwed upon the end of
the leg 2. The sleeve when screwed inward bears against the head 34 of the
plunger, preventing it from outward movement and the leg 10 from inward move-
inent, the set nut 46 being adapted to secure the sleeve in adjusted positions. As
the scale is carried by one leg and the indicator by the other, a minimum
measurement is thus fixed which represents the limit of approach of the points.
By the action of the plunger, the leg 10 may be thrust outward from the leg 2 to
disengage the feather 14 from its groove, and permit the leg 10 to be rotated to
laterally separate the caliper points.
In the modified construction shown in Figure 3, the inner caliper leg and plunger
are formed as one rod 50, the operation and adjustment being substantially the same
as in the other construction, the sleeve 20 being held from sliding movement by a
pin 41-engaging the circumferential groove 43 in the rod.
In measuring a boiler plate 52, a small bole 54 is bored through the plate near the
joint 56. The leg 10 of the calipers being then pushed outward, its hook 12.is
turned to the position shown by the dotted line in Figure 1, after which the hook 12
is inserted through the hole 54, and turned back to its. normal position when the
spring closes the points upon the plate, the inner point resting in the depression. 58
and the scale indicating the reduced thickness of the plate. The sleeve 39 is then
screwed inward until the plunger is held in bearing contact with the head 26, as
may be determined by the touch, and then secured by the set nut 46. The leg 10
is then thrust outward and turned to the dotted line position and the calipers
removed. By turning the leg 10 back to its normal position, the points are again
in alignment and the spring carries the leg 10 inward until stopped by the plunger,
which stopped by the sleeve 39, when the points are in the same relative
position as when the measurement was taken, and the reading of the scales may be
noted.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, as communicated to me 'by
my foreign correspondent, I declare that what I claim is :—
1. Calipers having a fixed leg and a slidable and rotatable leg.
2. The combination, with the stationary leg and the slidable rotatable leg, of
caliper points on said legs, means automatically closing the points when in alignment,
and means holding the points separated when out of alignment.
3. The combination, with the fixed, and the slidable and rotatable caliper legs,
of automatic means for closing the points, and adjustable means for limiting their
approach.
4. The combination, with a hollow cylindrical caliper leg and another slidable.
and rotatable therein, of points upon said legs offset from their axis, means for
holding said points in alignment with each other, means for automatically closing
said points, means for limiting their closing movement, and means for laterally
separating them.
5. The combination, with the caliper legs slidable and rotatable upon each other,
of means to prevent rotation when their points are in alignment, and means limiting
the approach of the points.
6. Calipers comprising in combination a fixed leg, an adjustable and rotatable
leg and a scale and indicator carried respectively by them.
7. The combination, with the caliper legs slidable and rotatable upon each other,
of a scale carried by one, an indicator carried by the other, and an adjustable stop
for said indicator,

page_text: 8. The combination, with the caliper legs adjustable in a right line upon each
other, of measuring devices upon said legs, and an adjustable stop fixing the
minimum distance between their points.
9: The combination, with caliper legs adjustable in a right line upon each other,
of measuring devices carried by said legs, and an adjustable stop for fixing the
minimum measurement of said devices.
D
11
1
1001
WM. P. THOMPSON & Co.,
Agents for the Applicant.