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8/2/2019 10 Outside Micrometer
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Lesson No.10
Week No.06
Lesson Name
Outside Micrometer
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OUTSIDE MICROMETER
Principle :- The Micrometer works on the principle of
screw and nut. The linear movement of the spindle during
one rotation is equal to the pitch of screw.
Uses :- Precision Outside linear measurement.
Range :- (Metric) :-
0-25mm, 25-
50mm 50-75mm, 75-
100mm (British) :-0-1, 1-2, 2-
3...... up to 12.
12-16, 16-20, 20-
24.
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Construction of Outside Micrometer
1. Frame :- The frame is made of
Cast iron on which the whole
assembly is attached.
12 2. Barrel/Sleeve:- Main scale is
graduated on it with 0.5 mm
distance.
3
3. Thimble:- Divisions are markedon this cylindrical portion.
Knurling is made on it for better
gripping.
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Construction of Outside Micrometer
4 4. Spindle:- Spindle is one of thecontacting surface during
measurement. It moves to and
fro as thimble rotated.
5
5. Anvil:- It is the another
contacting surface which is
fixed in Frame.
6
6. Lock nut:- This nut is used to lock the movement of the
spindle.
7
7. Ratchet:- Ratchet is used to apply uniform pressure during
measurement.
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Graduation of Outside Micrometer
In metric micrometer the pitch
of the spindle thread is 0.5 mm.
Thereby in one rotation of thethimble, the spindle advances
by 0.5 mm. On the barrel a 25
mm long datum line is marked.
This line is further graduated tomillimeters and half
millimeters. The graduations are
numbered as 0, 5, 10, 15, 20 and
25 mm.
Barrel
graduation
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Graduation of Outside Micrometer
The circumference of the bevel
edge of the thimble is graduated
into 50 divisions and marked 0-
5-10-15...45-50 in a clockwisedirection. The distance moved
by the spindle during one
rotation of the thimble is 0.5
mm.
Thimble
graduation
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Reading of Outside Micrometer
First note the minimum range of the outside micrometer.
While measuring with a 50 to 75 mm micrometer, note it as
50 mm.
Least Count:- The least count of a Metric Micrometer is 0.01mm. It is the ratio of value of 1 main scale division and total
graduations on thimble. i.e. 0.5/50
Then read the barrel graduations. Read the value of the
visible lines on the left of the thimble edge.
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Reading of Outside Micrometer
Then read the thimble graduations. Multiply these
graduations with least count.
Add all above reading together. The sum of these reading is
the actual reading of the object.
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Example of Reading - 1
In given figure first readthe barrel graduation.
Which is 13. i.e. 13 mm.
Half millimeter is alsovisible.
Thus 13.00 mm
+
00.50 mm
13.50 mm
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Example of Reading - 1
Next read the thimblegraduation, which is 13.
Multiply it by L.C. which is
0.01mm. = 13 x 0.01 mm
=0.13mm.
Summation of all above
readings,13.50mm
+0.13mm
13.63mm
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Example of Reading - 2
In given figure first read the barrelgraduation. Which is 7. i.e. 7 mm.
Half millimeter is not visible.
Next read the thimble graduation,
which is 31. Multiply it by L.C. which is
0.01mm. = 31 x 0.01 mm
= 0.31mm.Summation of all above readings,
07.00
+00.31
07.31 mm
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QUESTIONS
What are the parts of Micrometer ?
Which material is used in Out side micrometer ? What is the use of Out side micrometer ?
What is the principal of Out side micrometer ?
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CONCLUSIONThus, we learnt about Out side micrometer
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