Lesson No.10

Week No.06

Lesson Name

Outside Micrometer

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”.

Construction of Outside Micrometer

1. Frame :- The frame is made of Cast iron on which the whole assembly is attached.

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2 2. Barrel/Sleeve:- Main scale is graduated on it with 0.5 mm distance.

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3. Thimble:- Divisions are marked on this cylindrical portion. Knurling is made on it for better gripping.

Construction of Outside Micrometer

4 4. Spindle:- Spindle is one of the contacting surface during measurement. It moves to and fro as thimble rotated.

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5. Anvil:- It is the another contacting surface which is fixed in Frame.

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6. Lock nut:- This nut is used to lock the movement of the spindle.

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7. Ratchet:- Ratchet is used to apply uniform pressure during measurement.

Graduation of Outside Micrometer

In metric micrometer the pitch of the spindle thread is 0.5 mm. Thereby in one rotation of the thimble, the spindle advances by 0.5 mm. On the barrel a 25 mm long datum line is marked. This line is further graduated to millimeters and half millimeters. The graduations are numbered as 0, 5, 10, 15, 20 and 25 mm.

Barrel graduation

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 clockwise direction. The distance moved by the spindle during one rotation of the thimble is 0.5 mm.

Thimble graduation

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 0.01 mm. 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.

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.

Example of Reading - 1

In given figure first read the barrel graduation. Which is 13. i.e. 13 mm.

Half millimeter is also visible.

Thus 13.00 mm + 00.50 mm

13.50 mm

Example of Reading - 1

Next read the thimble graduation, 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

Example of Reading - 2

In given figure first read the barrel graduation. 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

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 ?

CONCLUSION

Thus, we learnt about Out side micrometer