Lecture 3 (Mehsjshsjsjsasurment Tools-2).pptx

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1. ME-101 Workshop Technology Precision Measuring Instruments Micrometer / Screw Gauge 1

2. 2 Outside Micrometers A micro meter is a precision instrument used to measure a job, generally within an accuracy of 0.01mm (Recall, it was 0.02mm for Vernier Caliper ) Micrometer used to take the outside measurements are know as outside micrometer. Principle :- The Micrometer works on the principle of nut and bolt. The linear movement of the spindle during one rotation is equal to the pitch of screw.

3. 3 Outside Micrometers Uses :- Precision Outside linear measurement Metric 0 – 25 mm, 25 – 50 mm, 50 – 75 mm, 75 – 100 mm English 0-1”, 1”-2”, 2”-3”...... up to 12”. 12”-16”, 16”-20”, 20”-24”. Ranges

4. 4 Construction of Outside Micrometers 1. Frame :- The frame is made of Cast iron on which the whole assembly is attached. 1 2 2. Barrel/Sleeve:- Main scale is graduated on it with 0.5 mm distance. 3 3. Thimble:- Divisions are marked on this cylindrical portion. Knurling is made on it for better gripping.

5. 5 Construction of Outside Micrometers 4 4. Spindle:- Spindle is one of the contacting 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.

6. 6 Construction of Outside Micrometers anvil spindle sleeve thimble ratchet frame

7. 7 Graduation of Outside Micrometers 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 (1 mm) and half millimeters (0.5 mm). The graduations are numbered as 0, 5, 10, 15, 20 and 25 mm. Barrel graduation

8. 8 Graduation of Outside Micrometers 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

9. 9 Reading of Outside Micrometers 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 When the anvil and spindle of the micrometer touch each other, the scales should read zero. If not, there is a zero error in the micrometer. Zero Error of Outside Micrometer Least Count of Outside Micrometer

10. 10 Zero Error of Outside Micrometer If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is positive. supposing observed reading is 2.37 mm, then corrected reading = observed reading – zero error = 2.37 – (+0.02) = 2.35 mm } 2 divisions

11. 11 Zero Error of Outside Micrometer If the anvil and spindle touch each other, but the scales do not read zero as shown below, the zero error is negative . supposing observed reading is 2.87 mm, then corrected reading = observed reading – zero error = 2.87 – (-0.03) = 2.90 mm } 3 divisions

12. 12 Reading of Outside Micrometers 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. First note the minimum range of the outside micrometer. While measuring with a 50 to 75 mm micrometer, note it as 50 mm. Then read the barrel graduations. Read the value of the visible lines on the left of the thimble edge.

13. 13 Example 1, Reading of Outside Micrometers 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

14. 14 Example 1, Reading of Outside Micrometers 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

15. 15 Example 2, Reading of Outside Micrometers 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

16. 16 Example 3, Reading of Outside Micrometers reading on sleeve = 4.5 mm reading on thimble = 0.12 mm actual reading of object = 4.5 + 0.12 = 4.62 mm thimble sleeve

17. 17 Practice Problems, English Micrometer How to Read 0 -1” Micrometer

18. 18 Practice Problems, English Micrometer

19. 19 Practice Problems, English Micrometer

20. 20 Practice Problems, Metric Micrometer Reading 0-25 mm micrometers

21. 21 Practice Problems, Metric Micrometer Reading 0-25 mm micrometers

22. 22 Inside Micrometer