Improvements in Calipers.
Year: 1897

page_text: Date of Application, 6th Apr., 1897-Accepted, 2nd Oct., 1897
COMPLETE SPECIFICATION.
Improvements in Calipers.
I, JOHN BYSTROM, a citizen of the United States of America residing at 50
West Randolph Street at Chicago in Cook County and State of Illinois, Mechanic
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:-
My invention relates to an improvement in the construction of inside and outside
calipers and the objects of this invention are to construct the instruments by
building them up of several thicknesses of thin metal material, thus making them
cheaper and at the same time have them of greater stiffness than those now in use,
and so to construct them that the points of the legs will be in the same line, and
to provide the ordinary or outside calipers with a spring testing finger so adapted
that the difference of 1-1000 of an inch either larger or smaller than the measure-
ment desired, and to which it has been previously set, can be readily ascertained.
By this method of construction there is much less work required than by the old
method as the center piece of one leg fits between the outer plates of the other leg,
thus making the joint without the expensive work of milling and slotting which
is required when the legs are made of single pieces. I attain these objects in a
manner hereinafter described and claimed.
Figure 1 is a plan view of the instrument, the legs slightly opened, having the
outer plate of one of the legs broken away, so as to show the testing finger.
Figure 2, a sectional view on line 2-2 of Figure 1.
Figure 3, a view of the inside calipers constructed by my improved method.
Figure 4, a plan section on line 4-4 of Figure 3.
A represents the caliper, A¹ being the legs thereof, and A³ the swivel, A³ the
points at which the measurement is taken.
As will be seen by reference to Figures 2 and 4 the instruments shown are made
of three pieces riveted together. B represents the guide and lock bar being the
center one and provided with a slot b. B' is a set screw which passes through one
of the outer plates, through the slot b and by means of male and female screw
thread is adapted to enter the plate on the opposite side locking the jaws in any
position when tightened.
The center plate on one of the jaws A¹ is cut away to accommodate the spring C
and the finger D. The spring is made a trifle less in thickness than the center
plate and is fastened in place by rivets or similar devices. The finger D is also a
trifle less in thickness than the center plate and is pivoted at C between the outer
plates and in the space left by cutting away the center plate, at or near the point
of the leg which comes in contact with the article measured, the end c below the
pivot C being allowed to project slightly beyond the point of the leg proper.
The opposite end turns about at right angles to the main portion of the
finger D and passes out through an opening & made by cutting away the center
plate and sides on the surface of an outwardly extending projection formed by
a portion of each plate used in the construction projecting beyond the line of the

page_text: leg of the caliper. The upper side of the projection d' and the under side of the
end 3 of the finger D are made circular of a radius equal to the distance from
pivot C.
The projection also has upon its upper surface, marks or graduations indicat-
ing the movement of 1-1000 of an inch of the end c¹ of the finger D but of course
would be further apart than 1-1000 of an inch, as for example suppose the distance
from the pivot c to the end c² to be twenty times greater than the distance from
c to the end c, the marks or graduations above mentioned would be 1/20 of 1000
or 1/50 of an inch apart. These graduations are made above and below a central
line or mark for the purpose of determining whether the piece examined is larger
or smaller than the measurement at which the instrument has previously been set.
E is a small set screw for the purpose of setting the finger 1 when desired at a
predetermined point.
The use and operation of the instrument is as follows, viz.: Suppose it is desired
to turn a piece of metal down to three-quarters of an inch in diameter and to have
it measure exact or at least to 1/1000 of an inch of the desired diameter. The
finger D is set, by means of the set screws E, so that the pointer end registers
exactly to the center line or graduation of the projection d' above mentioned;
the set screw B¹ is then loosened and the legs of the instrument set with the use
of an ordinary scale so that the points A³ are of an inch apart; the work is then
turned down to approximately of an inch, when the set screw E is withdrawn
allowing the free movement of the finger D; the instrument is then passed over the
work and the pressure against the end c of the finger 1) will cause said finger to
indicate on the marked surface of the projection d' whether the piece is too large
or too small in diameter, for if the pointer ce remains below the central mark it
will indicate that the work is too small and if it regísters above said center line it
indicates that the work is too large in diameter.
It will be seen from the above description that the device is especially con-
venient for those having the overseeing and inspecting of the work in any machine
shop as every piece may be readily tested for its accuracy.
While I have described the scale on this improved instrument as being 1/1000
of an inch, it is obvious that the said scale may be any fraction of an inch without
departing from the spirit of my invention.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:
1. The combination with a caliper having two legs and provided with means
for locking the legs thereof in any position, of a spring finger pivoted near its
end to a predetermined point near the point of contact of one of said legs in a
manner allowing the end of said finger below said pivot to come in contact with
the article measured, the opposite end terminating upon a graduated surface, said
surface having graduations above and below a center line, said second end of said
finger bearing a predetermined proportion to the said first mentioned end,
said finger being for the purpose of indicating a small fraction of an inch. when
taking a measurement, and means for setting said finger at the said center mark,
substantially as described.
2. A caliper constructed of three pieces of sheet metal riveted or otherwise
secured together, the center plate of one leg adapted to enter between the outside
plates of the other leg for the purpose of a joint or hinge, and for the further.
purpose of bringing the points of the legs in a direct line with one another and to
greater resistance to twisting strain, substantially as described.
3. A caliper having two rigid legs pivoted together at one end, one of said legs
being partially hollow and having a projection on its outer side, said projection
having a graduated surface on its upper edge, a finger contained in said hollow and
pivoted at a point near its lower end near the point of contact of said hollow leg
and projecting beyond the end thereof; the upper end of said finger bearing a

page_text: predetermined proportion to said lower end and terminating on said graduated
surface of said leg, substantially as and for the purposes set forth.
4. A caliper having two rigid legs pivoted together at one end, one of said legs
being provided with a finger pivoted at a predetermined point near the point of
contact of said leg and having one end projecting beyond the lower point of said
leg, the opposite end terminating upon a graduated surface formed on said leg,
said graduations being formed by one central line or mark and one or more lines
or marks on either side thereof, substantially as and for the purposes set forth.
Dated this 28th day of March 1897.
JOHN BYSTROM.