Surface measuring instruments NSQF LEVEL 4 Unit-3 Session 3
Surface measuring instruments
It is used as a measuring device to
measure the accuracies in alignment, eccentricity of the parts/components. Dial
indicators are also great for checking crankshaft run out, crank end play,
shaft thrust, and gear backlash, flywheel face run out, flywheel housing
concentricity, valve seat concentricity or piston deck clearance.
Dial gauge
"A dial gauge is like a fine watch. It
consists of a graduated dial, pointer, plunger and a clamp. It measures the
displacement of its plunger on a circular dial by means of a rotating pointer."
It works on the rack and pinion principle. The stem/plunger has rack Teeth. A set of gears engage with the rack. The pointer is connected to a small pinion. The small pinion is independently hinged. i.e. it is not connected to the stem.
The vertical movement of the stem is transmitted to the pointer through a set of gears. A spring gives a constant downward pressure to the stem. Thus any movement of the plunger causes a corresponding movement of the main pointer on a graduated dial. In addition to the main pointer the dial gauge has a secondary scale and a small pointer for indicating the number of revolutions made by the main pointer.
Zero setting of the main pointer of
the dial gauge can be done by rotating the dial face until ‘0’ line coincides
with the pointer. For use dial auge is attached to the magnetic mounting stand
and the base of the stand is held on flat surface. The contact point of the
Stem is brought into the contact with the part to be inspected.
The part is rotated or translated and
deviations in readings are observed on the dial face by the movement of
pointer.
Digital dial indicator/gauge:
Its use is similar to the dial
indicator/gauge and uses inductive measuring system and has LCD display. It has
on/off function, zero setting at any position, hold function and plus-minus
preset function. It is also used in conjunction with magnetic base stand. The
reading is displayed on the dial.
Telescopic Gauge:
Bore gauge :
A dial or vernier bore gauge measures a bore directly. The
gauge has three symmetrical anvils that protrude from the gauge body that are
connected to the dial or micrometer mechanism. As the knob is rotated it moves
the anvils in or out with respect to the measurements. The knob usually has a
slipping mechanism to take the feel out of the device and increase reliability
between measurements. The measurement given is the mean diameter of the three
anvils, and is usually good to 0.001 mm.
Dial bore gauge:
A dial bore gauge is a special tool, which is used to
accurately measure the inside diameter of a hole, cylinder or pipe and will
also detect ovality and tapers in bores. Dial bore gauges are useful in checking
for taper or out-of-round conditions in a cylinder bore as well as many other
inside machinists measurements. In conjunction with a micrometer, a bore gauge
will give the exact reading of a bore size. A typical bore gauge is comprised
of a shaft with a dial indicator at the top and a measuring sled at the base.
The measuring sled consists of three guides and an actuating plunger. Dial bore
gauges give quick and accurate readings on the size, less than perfect
roundness or wear.
Screw Pitch Gauges:
"Screw pitch
gauges are used to check the pitch of the thread immediately." It is very much
in everyday tool used to pick out a required screw. The number of flat blades
with different pitches is pivoted in a holder. The pitch value is marked on
each blade. To know the pitch of any thread (nut, bolt etc.), by visual
inspection the leaf is selected and placed on the profile of the thread. If the
profile of screw pitch gauge leaf matches with the profile of the thread being
inspected, the value of pitch is read from the leaf. If the profile does not
match, another leaf is selected and process repeated till the profiles matches.
It must be ensured that during matching air or light should not pass through
the profiles.
Feeler Gauges:
Feeler gauges are used for checking the clearance between mating surfaces. They are mainly used in adjusting the valve clearance and setting of spark plug gaps in automobiles. They are made from 0.03to 1.0mm thick of 100mm long leaves. The blades are pivoted in a holder. The value of thickness of the leaf is marked /engraved on it. To know or adjust the clearance/ gap, the leaf of the feeler gauge is selected and inserted in the gap, the leaf should not be loose or inserted with force. The leaf should go in the gap with slight drag/resistance. The value of the clearance/gap is read from the leaf of feeler gauge.
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