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Metrology Digital Caliper
The digital caliper has a long section with measurement markings. On one end, there is a pair of jaws. The outer jaw is fixed with the long section, and the inner jaw slides along the caliperโs beam to indicate the measurement. Most calipers have two sets of jaws. One pair measures the exterior of parts; the other pair measures interior dimensions. Calipers are versatile because they can measure both outer and inner lengths and diameters, as well as depth measurements. The range of most calipers is five inches or more.
Though they are more accurate than steel rules, calipers should not be used for precise measurements. The greatest sensitivity of most digital calipers is 0.001 inches. Different operators may apply different amounts of pressure when taking a measurement. This can create a range of readings.
Metrology Digital Caliper
External Measurement
Internal Measurement
Depth Measurement
Metrology Digital Caliper
External Measurement
Use the external jaws to measure external features like an outside diameter or width of a part or feature. When measuring external features with the external jaws, the operator would ideally read the smallest value attained while maximizing the contact area of the caliper jaws. Always ensure the jaws are gripping the work piece parallel / tangent to the faces being measured.
Correct Incorrect
Metrology Digital Caliper
External Measurement
When measuring external features with the external jaws, the operator would read the smallest value attained while maximizing the contact area of the caliper jaws. Ensure the jaws are gripping the work piece parallel / tangent to the faces being measured and that the jaws are not angled, reading the true value.
Correct
Incorrect
Metrology Digital Caliper
Depth Measurement
Ensure that when using the depth measuring blade to keep the end of the caliper square with your reference plane or face.
Metrology Vernier Caliper
Vernier Caliper Anatomy
Metrology Vernier Caliper
Each inch marker is divided into 10 equal segments, each 0.1โ in length.
Step 2
Find where the zero marker falls within the 0.1โ divisions.
In this case it is observed that the marker is between the 0.3โ and 0.4โ division.
Therefore, rounding down because we know we have at least 0.3, we add a value of 0.3โ Result
Metrology Vernier Caliper
Each 0.1โ marker is divided into 4 equal segments, .025โ in length.
Step 3
n= # of complete 0.025โ segments to the left of the zero marker. In this case, n=0 , therefore (n) X 0.025โ = 0.
Result
+0.
1 2 3 4
n
Metrology Vernier Caliper
Example 1
Example 2
Check with your instructor to verify your answers when finished.
Metrology Micrometer
The most common measuring device in the shop is the micrometer. The micrometer is a U-shaped device with a threaded spindle on one end and a small anvil on the other. The operator turns the spindle to gradually advance its end toward the anvil on the opposite side and close in on the part.
The typical micrometer only has a range of one inch (25.4mm), as shown above. Consequently, you would need different micrometers to measure distances between 0 and 1 inches, 1 and 2 inches, and so on.
A micrometer offers a balance of versatility and accuracy. A regular manual micrometer has a sensitivity that equals digital calipers (0.001). Manual micrometers with a Vernier scale provide sensitivity to 0.0001 inches.
Micrometer
Metrology Micrometer
Standard micrometer with 0.001โ precision
Step 2 Read largest value exposed on barrel scale. In this case we can see the 3, divide this value by 10 = 0. 0.000 +0.
Step 1 Determine the range of the micrometer. As this is a 0 โ 1โ, the value we read will be between 0 and 1, therefore, we know the first digit in our addition process to be zero.
Step 3 n= # of complete 0.025โ segments visible on the barrel scale. n = 2 so we add (n) X 0.025โ = 0.050โ 0.000 +0.3 +0. Step 4 Read value from thimble scale inline at the center of the barrel scale. In this case 24 lines up so we add 100024 = 0. 0.000 +0.3 +0.05 + 0.024 = 0.374โ
Metrology Micrometer
Standard micrometer with 0.001โ precision
3 x 0.025โ
0 1000 = 0.
= 0.375โ
3 x 0.025โ
1 1000 = 0.
= 0.376โ
Example 1
Example 2
Step 3
Thimble Scale reads between 20 and 21 so rounding down, we add 20 1000 =^ 0.020โ
Metrology^ Micrometer
Standard micrometer with 0.0001โ precision This micrometer has the addition of a Vernier scale to read values as small as 0.0001โ
Summary Barrel Scale = 0.500โ Barrel Scale (1) x 0.025โ Divisions = 0.025โ Thimble Scale = 0.020โ Vernier Scale = 0.0004โ 0.5 + (0.025) + 0.02 + 0.0004 = 0.5454โ
Step 4
Find two lines that are collinear and add value from Vernier Scale, in this case, 4 ๐ ๐๐๐๐๐ = 0.0004โ
Metrology Micrometer
Check with your instructor to verify your answers when finished.
Micrometer Examples 0.0001โ precision
