MICROMETER

                        Micrometer

The micrometer is a measuring instrument a which is  used to measure the external  and internal dimensions as well as the depth and heights. It has five main parts frame, anvil, sleeve thimble and spindle . The frame is ' U ' shaped and made of steel. In this the gap of the frame permits the maximum dimension that can be measure on the left end of the frame, the anvil is fixed at a right end, there is a screwed spindle. 

 

The diameter of the anvil and spindle should be equal . A lock nut is provided to lock the spindle to retain the reading. The sleeve has reference line and main scale on it. A tubler cover  fixed with spindle is called thimble . Thimble moves with spindle on main scale . Thimble has 50 equal parts on it's bevelled edges. This is called as circular or vernier scale. Reatchet  screw is provided to tighten the thimble. When correct reading  achieved ratchet slips automatically. 

Least count-: The least distance which can be measured accurately with micrometer is called least count.

Least count = pitch of the spindle screw 

                         No. Of division on thimble 

                     = 0.5 / 50    = 0.01 mm

Reading of micrometer -:  

Reading uncovered on sleeve + ( least count × no of division on thimble with R.F. line )

Reading = 10.5 + ( 0.01 × 15 ) = 10.65 mm

Types of micrometer -: 

1. Outside micrometer 

2. Inside micrometer 

3. Screw thread micrometer 

4. Depth gauge micrometer