METROLOGY

“

When you can measure what you are speaking about, and express it in numbers, you know something about it: but when you cannot measure it, when your cannot express it in numbers your knowledge is of a meagre and unsatisfactory kind;…”

Lord Kelvin, 1883

Metrology Metrology is “The science of measurement” Used to

communicate about : Size Quantity Position Time Etc.

Why Measure

If you can’t measure it: You can’t make it If you can’t measure it: You can’t control it You can’t manage it You can’t improve it

Measurement Errors

All Dimensional Measurements = Actual Size +/- ErrorsMeasurement errors must be controlled Error = The difference between the

actual size and the measured size

Sources of Measurement Errors

Part Operator Instruments Standard Environment

Ten-To-One Rule

If Part Tolerance = 0.01”ThenGage Discrimination =0.001”

Calipers – The Original Transfer Instruments

Types of CalipersSimple Caliper Instruments

Types of Calipers

Line of Measurement- Outside Caliper

Line of Measurement- Outside Caliper

Line of Measurement - Inside Caliper

The Combination Square

This is one of the most useful of the steel rule variations. It is rarely used in any kind of production inspection. However, it is used universally in tool and die making, pattern making, model and prototype work, and for machine setup.

The combination square consists of a blade and a square head. The most popular is 4 inches long.

The Combination Square

Square Head

1. It provides a right angle reference 2. It provides a means for transferring either the measured point or the reference point for the work to the rule.

Square HeadDepth Measurement

Protractor Head

It provides a convenient means for checking angles no closer than 1°. Its chief advantages are convenience and rugged construction.

Center Head

In contrast to the steel rule method for measuring diameters, the center head method is far more reliable.

Center Head

For layout purposes the center head provides on of the most satisfactory methods for finding the centers of shafts.

Vernier Caliper

Vernier Reading The Reading steps are as follows

1. Read the number of whole inches one the main scale that appear to the left of 0 on the vernier.

2. Read the highest numbered graduation on the main scale that lies to the right of the index(0) on the vernier scale. Read these graduations as even one hundred mil(0.100, 0.200, etc).

3. Read the highest number of whole minor divisions to the right of the index. Read these graduations as even twenty-five mil (0.000,0.025,0.050 and 0.075 in.). Add to the sum of steps one and two (1.125,1.150 in., etc.).

4. Now find the vernier graduation that most perfectly coincides with any graduation on the main scale. That is the nearest mil and may be any whole number from zero to 25(0.000, 0.001,….0.024,0.025). Add this to the sum of the previous three steps.

Vernier Reading

Advantages and Disadvantages of Vernier Scales

Practices