Vernier Instruments

Chapter 6

Vernier Instruments

Invented by Pierre Vernier in 1631

Vernier Instruments

1851 Brown & Sharpe applies the vernier principle to the slide caliper

The inch vernier scale has 25 divisions in the same length that the main sale has 24 divisions.

The difference between a main scale division and a vernier division is 1/25 of 0.025 inch or 0.001”

Reading a vernier (Pg. 107, 108)

Advantages & Disadvantages (Fig. 6-7)

Vernier Caliper

Can economically provide measurements from 6”-80”.

Can be substituted for many micrometers but can’t replace them.

Reliable measurements depend upon good alignment.

Abbe’s Law

“maximum accuracy may be obtained only when the standard is in line with the axis of the part being measured.”

The Interchange Method

Observing both ends of the measured part at the same time (Fig. 6-10)

The Displacement Method

Same longitudinal movement on both the part and the standard and relate these two movements to each other.

Positional error (Fig. 6-11)

Importance of the Clamping Screw

Minimizes positional error by locking the movable jaw to the beam

Measurement with Vernier Calipers (Fig. 6-9)

Read the proper side for the measurement you are taking

Alignment Consideration (Fig. 6-13, 6-14)

Must develop sense of gaging feel

Outside Diameter (Fig. 6-15)

Easiest to measure

Strive for perpendicularity

Inside Diameter

Practice centralizing jaws inside of hole

Flat Surfaces (Fig. 6-16)

Be wary of spring and compression forces

Accuracy checks for Vernier Calipers Manipulative Error

Manipulation error is the most common form of unreliable readings

Jaw Wear (6-18)

No greater than 0.0002”

Check for light gap (Fig. 6-18)

Repeatability

Used to check for accuracy using standards

Zero Setting

Dial Calipers (Fig. 6-23)

Will malfunction more often than vernier

Accurate to 0.001 per 6”

Used by less skilled people

Electronic Digital Calipers (Fig. 6-24)

Greatest benefit is the computer connection

Convert easily from english to metric

Floating zero for plus or minus deviation readings

Automatic comparison to tolerances

Computer connectivity for printing results or performing SPC

Vernier Depth Gage (Fig. 6-25)

Vernier Height Gage (Fig. 6-28)

Accuracy to 0.001”

Most important use of the scriber is for layout rather than measurement

An indicator will minimize the need for “feel” with height measurements

Dial and Electronic Height Gages

Using the Height Gage

Checking the Height Gage

Base to column squareness

Check for burrs and nicks

Truly flat base will “wring” to a fine surface plate

The best way to test accuracy and precision is to make repeated readings of gage block heights at various points throughout the range.

The Problem with Height Gages (Pg. 126-127)

Height to base ratio

Three Elements of Measurement

1. Object to measure
2. The standard of length to compare it to
3. The means for comparison

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1/14/2019