John F. Ross C.V.I. Manufacturing Technology

Parts of an Outside Micrometer: VERNIER SCALE

ANVIL

THIMBLE

SPINDLE

BARREL / SLEEVE LOCK

FRAME

RACHET

John F. Ross C.V.I. Manufacturing Technology

Graduations on the Sleeve and the Thimble

FOUR GRADUATIONS = 4 X 0.025 = 0.100

EIGHT GRADUATIONS = 8 X 0.025 = 0.200

EACH GRADUATION ON THE SLEEVE = 0.025 OR TWENTY FIVE THOU.

EACH GRADUATION ON THE THIMBLE = 0.001 OR ONE THOU

One complete revolution on the Thimble = 0.025. One complete revolution on the Thimble will advance its edge one graduation on the Sleeve.

John F. Ross C.V.I. Manufacturing Technology

Graduations on the Vernier Scale

VERNIER SCALE PRINTED ON THE SLEEVE

THERE ARE ONLY 10 GRADUATIONS ON THE VERNIER SCALE = 10 X 0.0001 = 0.001

EACH GRADUATION ON THE VERNIER SCALE = 0.0001

John F. Ross C.V.I. Manufacturing Technology

The two Reference Lines used in Reading a Micrometer: REFERENCE LINE #1 - ON THE SLEEVE

VERNIER SCALE

REFERENCE LINE #2 – EDGE OF THIMBLE

READ WHERE THE TWO REFERENCE LINES INTERSECT

When any number on the Thimble lines up with the reference line on the Sleeve, Vernier scale is ignored.

John F. Ross C.V.I. Manufacturing Technology

3 STEPS TO READ A MICROMETER (INCH)

STEP 1 – ADD ALL GRADUATION FROM ZERO TO EDGE OF THE THIMBLE = 0.825

STEP 2 – FIND THE NUMBER ON THE THIMBLE THAT LINES UP ON REFERENCE LINE ON THE SLEEVE = 0.005

STEP 3 - COMBINE STEP 1 WITH STEP 2 0.825 +0.005 = 0.830

Since the number 5 (0.005) on the Thimble lines up with the Reference line on the Sleeve, the Vernier scale is ignored.

John F. Ross C.V.I. Manufacturing Technology

Reading the Vernier Scale on the Micrometer:

REFERENCE LINE

NO LINE ON THE THIMBLE LINES UP WITH THE REFERENCE LINE

0.005 0.625

When no line on the Thimble lines up with the Reference line on the Sleeve, the Vernier scale is used. The reading above = 0.625 + 0.005 = 0.630

John F. Ross C.V.I. Manufacturing Technology

By slightly rotating the Sleeve, graduations on the Vernier scale will be exposed. Below shows 0.0005 reading on the Vernier scale. This value will be added on the 0.630 above. Therefore 0.630 + 0.0005 = 0.6305 this is the final reading.

THIS LINE ON THE THIMBLE LINED UP WITH THE NUMBER FIVE OF THE VERNIER SCALE. NUMBER 5 WILL BE USED. NUMBER 5 = 0.0005 or HALF A THOU