https://anilitistudy.blogspot.com-INTRODUCTION OF-OUT SIDE MICROMETER-VERNIER MICROMETER-SCREW THREAD MICROMETER-FITTER ONLINE NOTE

INTRODUCTION
1-Micrometer is a precision measuring instrument.
2-Its accuracy is 0.01 mm or 0.001 inch.
3-Its working principal is NUT and BOLT.
4-Its available in difference size 0-25, 25-50, 50-75 ………… 125-150.
5-The different types of micrometer available in market.Outside       micrometer, Inside
      micrometer.Depth Micrometer, Thread Micrometer.Vernier Micrometer.

Parts of Micrometer – Frame, Anvil, Spindle, Sleeve and Barrel, Thimble, Luck Nut, Ratchet Stop.

FRAME-

1)- It is made by drop-forged steel or malleable cast iron.
2)-All other parts attached to this frame.
ANVIL-

1)-It is one of the measuring face.
2)-It is fixed by frame.

3)-It is made by alloy steel.
SPINDLE-

1)-One end of the spindle is the measuring face.
2)-Other end is thread and passes through a nut.
3)-The thread mechanism allows for the forward and backward movement of the spindle.
SLEEVE & BARREL- 

1)- It is fixed to the frame.

2)- The datum line and graduation are marked on this.
THIMBLE-

1)- On the bevel surface of the thimble also, the graduation is marked.
2)- The spindle is attached to this.
LUCK NUT -

1)- It is used to luck the spindle at a desired position.
RATCHET STOP - 

1)- The ratchet stop ensure a uniform pressure between the measuring surface.

LEAST COUNT OF OUT SIDE MICROMETER-
1- In metric micrometers the pitch of the spindle thread is 0.5 mm.

2- In one rotation of the thimble, the spindle advances by 0.5 mm.

3- The circumference of the bevel edge of the thimble is graduated in to 50 division and marked 0-5-       10-15......45-50 in a clockwise direction.
4- completely 50 division rotated by thimble the spindle moved 0.5 mm
5- completely 1 division rotated by thimble the spindle moved 0.5/50=0.01 mm
6- Accuracy or least count of a metric outside micrometer is 0.01 mm.
CALCULATE THE READING- Range of micrometer 0-25mm.

1)- First minimum rang of micrometer = 0.00 mm

2)- Sleeve/Barrel reading is                  = 7.00 mm

3)- Thimble Reading(37 x 0.01)          = 0.37 mm

                                                                                  .                                                                                   ADD ALL                         = 7.37 mm

VERNIER MICROMETER READING-

10th division of vernier scale on sleeve = 9th division of thimble.

One scale of vernier scale on sleeve = 9/10th division of thimble.

One division of thimble = 0.01 or 1/100

9/10th division of thimble = 1/100 x 9/10 = 9/100 mm

What is the difference between one thimble division and one vernier scale division ?

1 Thimble Division - 1 Vernier Division = 1/100 - 9/1000 

= 10-9/1000 = 1/1000 mm or 0.001 mm or 1 micron(Least Count)

example - 

Value of one Main Scale Division (5 x 1 mm) = 5.000 mm  

Value of one Sub Scale Division (1 x 0.5 mm) = 0.500 mm

Value of one Thimble Scale Division (28 x 0.01 mm) = 0.280 mm

Value of one Vernier Scale Division (3 x 0.001 mm) = 0.003 mm                   

ADD ALL= 5.000 mm + 0.500 mm+0.280 mm+0.003 mm

=5.783 mm( Actual Reading of vernier micrometer)

Screw thread micrometer:-

i)- This micrometer is used to measure the effective diameter of the screw threads.

ii)- It is an instrument used for measuring pitch diameter of screw thread.

iii)-It consists of the same parts as the outside micrometer except that the movable spindle is pointed.

iv)-The end of the anvil is of the same form as the screw thread to be measured. 

v)-In measuring screw threads, the angle of the spindle point and the sides of the anvil contact the surface of the thread So that the reading of the instrument indicates the pitch diameter of the thread. 

vi)-The set of interchangeable anvils is also made to suit particular threads.

vii)- To suit a variety of pitches, a different range of micrometers are necessary.