Introduction to Measurement and Metrology

Lecture Video

Lab 1 – Measurement

Part 1 - Setting a sine bar

• Gage Blocks
• Sine Bar

Part 2 - Determining the angle from a sine bar

Part 3 - Reading a metric micrometer

Part 4 - Reading an inch micrometer

Part 5 - Reading dial calipers

Part 6 - Reading vernier calipers

​

Typically measured values

• Part dimensions - Interchangeable parts
• Size
• Orientation
• Form
• Location
• Time
• Weight
• Temperature
• Pressure
• Hardness

Is this part exactly .5 inches?

These symbols are GD&T

Core Metrology Concepts

• Precision - the quality of being clearly defined or how close the indicated value is to the true value (how tight is the pattern?)
• Accuracy (bias) - the degree to which an indicated value conforms to an established standard (close to target)

​

• Resolution - referring to the fineness of the tool’s graduations. A rule graduated in 1/2 mm a higher resolution than one graduated in whole millimeters (should be 10X the tolerance)

​

• Repeatability - the degree of consistency achieved with a measuring tool, with a single reader measuring the same dimension several times
• Reproducibility - the degree of consistency achieved when a measuring device is used by different readers to inspect the same part or part dimension
• Repeatability and Reproducibility are measured using Gage R&R analysis

Calibration and Gage R&R

It is important to periodically evaluate the performance of measuring instruments.

​

• Calibration

Comparing the measuring tool to a standard of known accuracy to detect, correlate, report or eliminate variation in accuracy.

​

• Gage R&R (Repeatability and reproducibility)

Determine how reliable the instrument and procedure is in relation to the tolerance or variation in product. (video)

​

​

Two Systems

• English
• U.S. Customary
• Imperial
• Metric (SI)
• Need to know how to convert units of length.
• 25.4

Know Decimal Equivalents of Fractions

Fractions are almost never used in machining. Know theses common decimal equivalents.

​

(If you measure a part to be 1.124 inches wide, it is likely supposed to be 1.125)

Non-Graduated

Measurement Tools

Many of these tools are also used as “layout tools”

Surface Plate

Usually granite

Known to be flat within a tight tolerance

Used as an internal, primary standard

Gage Blocks

Should be NIST traceable

Example

Are used in combination

Internal primary reference

NIST

NIST is the last word on what makes a measurement correct in the United States.

​

Some Extreme Cases…

https://www.reddit.com/r/Chinesium/comments/kp2i2o/bad_tape_measures/

https://www.reddit.com/r/funny/comments/hsk8nw/measure_twice_and_cut_oncebut/

Dividers

Copy a measurement

Calipers

Used to measure opposite sides of an object. Can be graduated or non-graduated.

Firm Joint Calipers

Spring Joint Calipers

Outside Calipers

Inside Calipers

Odd-Leg Caliper

Also called “hermaphrodite” caliper

Used to layout a distance from an edge

​

Slide Calipers

Different types. Discussed later.

Hole Measurement

Telescoping Bore Gage

Hole Measurement

Small Bore Gage

Squares

Machinist’s Square

Combination Square

​

Protractor Head

Combination Square

Centering Head

Machinist’s Square

Adjustable Parallels & Planer Gages

Use to establish reference height

Planer Gage

Adjustable Parallels

Radius Gage

Thread Pitch Gage

Leaf style gage shown

Feeler Gage

Also know:

Shim stock can be purchased in precise thicknesses.

Go-NoGo Gage

Various types available

Does not inspect roundness

Sine Bar

Often used with gage blocks and surface plate.

• Height of Gage Blocks = Hypotenuse * sin(angle)
• Angle = asin(height/hypotenuse)
• Be sure your calculator is in DEGREE mode

Graduated measuring tools & gages introduction

• Rules (see review)

​

Graduated measuring tools & gages introduction (cont’d)

• Micrometer
• How to read a micrometer
• Depth micrometer
• Dial indicators
• The dial caliper
• Other tools incorporating dial indicators
• Height Gage

Vernier Caliper (Inch) see metric here

Video: How to Read a Vernier Caliper

Verniers in Other Instruments

Reading a Dial Caliper

Zero the Dial first

Read to the slide

Read the Dial

Ways to measure

Two things:

1. Use the thimble ratchet to “tighten”
2. A general rule: If you ever break anything in lab LET ME KNOW.

​

Video: How to Read an Inch Micrometer

Metric Micrometer Scale

​

Advanced measuring devices

• Optical Measuring Projector (optical comparator)

• Vision Systems, Video Microscopy

• The coordinate measuring machine (CMM)

Review & More Detail

Universal Bevel Protractor

​

Measuring Tools in the Machine Shop

​