Note: Descriptions are shown in the official language in which they were submitted.
7403- 1
This invention relates to a brake drum
measuring apparatus.
Periodically it is necessary to check the wear
of vehicle brake drums to determine if the drums are
within a prescribed tolerance range. This tolerance
range, set by the manufacturer, ensures that the brake
drums are still within a certain internal diameter and,
secondly, either perfectly round or vary from perfectly
round by a tolerable amount.
If a brake drum's internal diameter does not
fall within the prescribed ranges then the drum may be
machined or, if the internal diameter is too large, must
be replaced.
Brake drum measuring apparatus are used to
measure the internal diameters of brake drums to see
whether the drums meet the manufacturer's specification.
Prior art known to applicant includes U.S.
patents 4,520,568 to Drenner; 3,827,153 to Mitchell;
3,190,006 to Madeira; 3,192,634 to Johnqon; 2,769,241 to
Barrett and 3,1979874 to Fox. Of the above Drenner
discloses a brake drum guage with a flat, U-shaped frame
and micometer. The apparatus in Drenner depends on a
reference pin and different si~es of brake shoes can be
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measured by using different lengths of reference pins and
corresponding supports for that pin.
Mitchell discloses a device whose principal
function is to allow the clearance between brak~ drums
and shoes to be accurately set.
Madeira teaches a brake drum gauge composed of
two sections that slidably engage each other.
Johnson shows a dimensional gauge for large
diameters. The apparatus in Johnson includes gauging
rolls inserted between the surfaces to be measured.
Barrett is a brake gauge has a coarse measuring
gauge imprînted on a guide. A body 6 is slidably
received on the guide and a mechanically operated micro-
meter with a scale and needle is operated through a
series of gears.
Fox teaches a marking gauge includes a
measuring instrument with an adjustable slide bar.
or the above it is believed that Barrett is the
most pertinent.
The present invention seeks to provide an
accurate and convenient, lightweight apparatus to measure
the internal diameter of a brake drum. It is a par-
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ticular feature of the present inven-tion -that the apparatus
can be used while the bxake drum is in place on the vehicle
and grea-tly facilitates the use of such brake measuring
apparatus compared wi-th -the prior artO
Accordingly, the presen-t invention is a brake drum
measuring apparatus comprising:
a receiving bracket having a rnain portion with a
longitudinal cavity and a distal, depending portion for
mounting a pin to abut against the inner circumference of a
brake drum;
a gauge member slidably received within the
longitudinal cavity of the receiving bracket, having a main
portion with a coarse measuring scale, an actuating means for
operating a fine measuring scale, a dis-tal depending portion
for mounting a pin to abut against the inner circumference of
a brake drum;
locking means for fixing the position of the gauge
member in the longitudinal cavity of the receiving bracket;
fine measuring scale means mounted on said
receiving bracket cooperating with said actuating means of
said gauge member as the gauge member slides in the
longitudinal cavity; and
a pointer mounted on said receiving bracket to
point to the coarse measuring scale, said distal depending
portions of said receiving bracke-t and said gauge member
comprising coplanar first portions extending from said main
portions in an essentially vertical plane, said first
portions being bent to form
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coplanar second portions ex-tending out of said vertical
plane, each of said second portions providing a mounting
location for one of said pins, said pins defining an axis
that is parallel to the longitudinal cavity of said receiving
bracket.
Aspec-ts of the invention are illustrated, merely be
way of example, in the accompanying drawings in which:
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Figure 1 is an isome-tric projection o:f ~n appara-tus
of the present invention;
Figure 2 is a section 2-? in Figure 1;
Figure 3 is an isometric view similar -to Fiyure 1,
of a further embodiment of the inven-tion;
Figure 1 shows a prefer:red embodimen-t of the
present invention suitable for measuring larger diameter
brake drums without removal of the wheel. The appara-tus 10
comprises an essentially inverted U-shaped s-tructure formecl
from a receiving bracket 20 and gauge member 30. ~he main
portion 30 of the gauge member is slidably received within
the cavity 2~ of the main portion of the receiving bracket
20. At its opposite end, gauge member 30 is bent downwardly
through about 90 from the horizon-tal axes of the gauge
members main portion to form descending arm 3~ whicn, in
turn, is bent upwardly out of the vertical plane of the
inverted U shape to form arm 33 at an angle of 135 -to the
side face of descending arm 3~. Pin 42 is mounted towarcls
the free end 3~ of arm 33 to abu-t against the internal
circumferential surface of a brake drum.
At that end of the horizontal portion of the
receiving bracket 20 opposite -the entry point for gauge
member 30 is a second angle arm affixed in any suitable
manner to the main portion of receiving bracket 20,
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and shaped to present a mirror image o~ the angle arm
formed from gauge member 30. Descending arm 1~ is bent
into arm 19 with threaded hole 21 drilled through it. An
adjustable pin 40 with a corresponding threaded outer
circumference is threadably received in hole 21. It can
be secured in place using lock nut 22. Pins 40 and 42
are coaxial with and at opposite ends of horizontal axis
B-B which is in turn is parallel to horizontal axis A-A
allowing coarse scale 32 on axis A-A to be used to indi
cate the distance between the ends of pins 42 and 40 on
axis B-B. Receiving bracket 20 has a horizontal portion
with an enlarged cross section and central cavity 24 to
house gauge member 30. Receiving bracket 20 and internal
cavity 24 are of sufficient length to fully accept the
horizontal portion of gauge member 30. Coarse scale 32
inscribed on one surface of gauge member 30. Scale 32 is
is positioned on gauge member 30 such that pointer 37,
mounted to receiving bracket 20, always indicates the
distance between the ends of pins 42 and 40. To obtain a
more accurate measure of the distance between pins 40 and
42 than coarse scale 32 can provide, dial gauge 12 is
provided to act as a vernier gauge. Dial gauge 12
comprises a housing 13 with a centrally mounted, rotating
ponter 15 and circular scale 17 contained therein,
beneath a transparent cover 11. Dial gauge 12 operates
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such that each time pointer 37 moves between any adjacent
markings on coarse scale 32, rotating pointer 15 de-
scribes one full revolution of circular scale 17 and, in
doing so, rotating pointer 15, divides the distance bet-
ween adjacent markings on coarse scale 32 into smaller
units as indicated on circular scale 17 of dial gauge 12.
Dial gauge 12 performs its vernier scale func-
tion using a rack and pinion system to drive a rotating
pointer 15. Rack 34 extends the horizontal len~th of
gauge member 30 with serrated inner edges 35 and 36.
Geared drive wheel 29 held in rack 34, is connected
through a shaft 31 and a series of gears (not shown) to
rotating pointer 15. Dial gauge 12 is mounted atop
receiving bracket 20 and shaft 31 extends through an
opening in receiving bracket 20 to communicate with
geared drive wheel 29 in rack 34. As gauge member 30 is
moved back and forth in cavity 24 of receiving bracket
20, geared drive wheel 29 rotates due to the horizontal
motion of rack 34. This rotary motion is transmitted
through shaft 31 and an appropriate gear system to move
rotating pointer 15 an appropriate distance relative to
circular scale 17 of dial gauge 12 to indicate the small
horizontal distance travelled by rack 34.
Dial gauge 12 is also equipped wi~h lock button
16. When depresed this button 16 locks the dial gauge in
position.
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Locking screw 14 extends through the side wall
of receving bracket 20 and can be used to lock gauge
member 30 in place relative to receving bracket 20. By
rotating the screw inwardly until gauge member 30 is
clamped between the ends 23 of the locking screw 14 and
the opposite wall of cavity 24, the appropriate locking
is achieved.
The present invention also includes a calibra-
tion bar 50 of a predetermined length between its two end
tabs 51 and 52. In order to calibrate the present invet-
nion, the gauge member 30 is positioned in receving
bracket 20 such that pointer 37 of coarse scale 32 and
rotating pointer 15 of dial gauge 12 indicates the known
length of the calibration bar. Pins 40 and 42 are
inserted between end tabs 51 and 52 of calibration bar
50. If necessary, adjustable pin 40 can be moved
inwardly or outwardly, after loosening lock nut 22, to
ensure that pins 40 and 42 span a distance equal to that
indicated by the calibration of the coarse scale and dial
gauge.
The first embodiment of the invention can
be used while the brake drums are still in place on the
vehicle. After removing the brake drum and inspection
plate, the U-shape of the apparatus of the present inven-
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tion allows it to fit around the vehicle's axles and thedescending arms are formed so as to allow pins 40 and 42
to be inserted into the interior of the brake shoe.
Inside the brake drum pins 40 and 42 abut against the
internal braking surface of the shoe. Coarse gauge 32
and dial gauge 12 in combination give an accurate
measurement of the internal diameter of the brake drum.
Thus brake drum wear can be instantly deter-
mined to see whether the internal diameter is still
within a predetermined range fixed by the manufacturer.
If not, replacement of the brake drum is necessary.
The embodiment of Figure 3 is for use with
smaller brake drums. In Figure 3, where appropriate 9 the
same reference numerals are used where the item is also
described in Figure 1. In the embodiment of Figure 3
descending arms 38 and 18, to which pins 40 and 42 are
mounted, are mounted vertically beneath horizontal axes
of gauge member 30 and receiving bracket 20.
In using the embodiment of Figure 3 of the pre-
sent invention the brake drum to be inspected is first
removed from the vehicle. Arms 38 and 18 are inserted
into the brake drum and pins 40 and 42 brought into con-
tact with the drums internal braking surface. The drum's
internal diameter can be read from the coarse scale 32
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and dial gauge 12, to determine whether the drums are
within manufacturer's tolerance.
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