Measuring Tools

Introduction

Measuring tools for small engines are divided into three categories.

– Direct reading

– Measurement transferring

– Reject gages

Direct Reading Measuring Tools

Small engines use two types of direct reading measuring tools:

1. Micrometers

2. Calipers

Micrometers

Micrometer Introduction

• A micrometer is a mechanical device

designed to measure distances as small

as 1/10,000 of an inch (0.0001 in).

• Micrometers are only one (1) inch long.

• The micrometer is used with different

types and sizes of frames to provide

precise measurements of many different

objects.

• Small engines uses three (3) types of

micrometers:

1. Micrometer caliper

2. Inside micrometer

3. Depth gauge micrometer

Micrometer calipers are available in mechanical and digital models.

Micrometer Caliper

• A micrometer caliper uses a frame that allows the

micrometer to measure the thickness of objects.

• For small engine use, different frame sizes are used to

provide a wider measurement range.

– One inch

– Two inch

– Etc.

Reading Micrometer Caliper-parts

• The first step in being able to read a micrometer is learning the

names of the parts.

� The face of the anvil and the

face of the spindle are the

contact surfaces.

� The spindle and thimble turn

together.

� The ratchet/friction stop

improves the repeatability of

measurements for beginners.

� A micrometer caliper is read

at the point were the edge of

the thimble crosses the barrel

scale

• Insure the lock is released before trying to turn the thimble..

Reading Micrometer Caliper-barrel

• A micrometer caliper is read

just like an ruler.

• Start by determining the

smallest whole unit, and then

determine the values of each

sub division.

• The smallest whole unit is

determined by the frame size.

– One (1) inch frame = 0.0

smallest whole unit

– Two (2) inch frame = 1.0

smallest whole unit.

– Etc.

• The micrometer barrel scale is

one (1) inch long and is

divided into ten (10) sections.

• Each number on the barrel

scale = 1/10 or 0.1 inch.

Reading Micrometer Caliper-barrel

• Each 1/10 of an inch on

the barrel scale is divided

into 4 segments.

• Each short line = 0.25 inches (25

thousands of an inch).

1

10÷ 4 =

1

10 x

1

4

=1

40= 0.025

Reading Micrometer Caliper-thimble

• The last step is reading the value on the thimble scale.

• The thimble scale subdivides the last segment on the barrel

scale.

• The smallest segment on the barrel

is 25 thousands (0.025).

• The thimble is divided into 25

segments = 1/1,000 or 0.001 inch.

Micrometer Caliper Example

• Determine the reading for the micrometer caliper in the illustration.

1. Smallest whole unit 0.000

2. Tenths of an inch 0.300

3. Twenty five thousands ( 0.025 x 2 ) 0.050

4. Thousands 0.015

Sum (measurement) 0.365

Micrometer Caliper-digital

• Most measuring tools

are available with a

digital readout.

• Advantages

– Easier to read.

– Can be interfaced with data collection devices

for automatic recording.

– Easy to convert between English and metric units.

• Disadvantages

– Requires battery

– More expensive

Inside Micrometer

• Inside micrometers have

been replaced by dial

calipers and other tools for

small gas engines.

• The principles for reading

are the same.

• The primary difference is

determining the smallest

whole unit.

• The physical size of the micrometer limits the

smallest whole unit to 1 or 1-1/2 inch.

• Extensions are added to set the minimum size

to the desired range.

Inside Micrometer Example

Read the inside micrometer in the illustration.

Smallest whole unit 1.500

Tenths 0.200

Twenty Five Thousands 0.025

Thimble 0.014

Sum (reading) 1.734

Inside Micrometer Example 2

• Inside micrometers use extensions to change the range of

measurements.

• Adding an extension increases the minimum measurement.

Smallest whole unit 2.000 Tenths 0.200

Twenty five thousands 0.075 Thousands 0.001

Reading 2.276

In this example a 1/2 inch

extension has been added.

Note: when the zero on the thimble is close to the reference line and a 25 thousands line is close to the edge of the thimble, it may be difficult to

determine if the last line that should be counted. If the thimble zero is above the reference line the line is not counted. If it is below it should be counted.

Depth Gauge Micrometer

• Depth gauge micrometers are

used to measure the depth of

blind holes, slots, key ways,

etc.

• The spindle length can be

changed to set the

micrometer for the desired

range of measurement.

• To read a depth gauge

micrometer you must

visualize the distance that

has been covered by the

thimble.

Thimble

Spindle

Depth Gauge Micrometer Example

Smallest whole unit 0.000

Tenths 0.800

Twenty Five Thousands 0.050

Thousands 0.017

Sum (reading) 0.867

Read the depth gauge micrometer in

the illustration

Calipers

Introduction

• Calipers can be direct reading or measuring transferring tools.

• Direct reading calipers are capable of a wider measurement

range than micrometer calipers.

– Six (6), eighteen (18) and twenty four (24) inch are popular.

• Three common designs of direct reading calipers;

– Vernier

– Dial

– Digital

Vernier Caliper

• Vernier calipers are an old tool that has been mostly replaced

by dial and digital calipers.

• They are manufactured with decimal scales, metric scales and

fractional scales.

• The Vernier scale is still used on many mechanical measuring

tools.

Vernier Scale

• The reference point is the 0 on the vernier scale.

• To read a Vernier, the line of coincidence must be located.

• The line of coincidence (LOC) is the line on the Vernier that

coincides with a line on the main scale.

– Illustration LOC = 19

• In theory only one LOC is possible, but usually when reading the

vernier it appears several exist. When this occurs pick the

middle line.

• A Vernier is a

mechanical means of

magnifying the last

segment on the main

scale so addition

subdivisions can be

made.

Vernier Caliper-practice

• Smallest whole unit 1.000

• Tenths of an inch 0.200

• Twenty five thousands 0.000

• Vernier scale 0.011

Sum (measurement) 1.211

LOC

Read the Vernier caliper in the illustration.

Dial Caliper

A dial replaces the Vernier.

This makes the caliper easier to read.

The reader must still determine the units and graduations.

Measurement Transferring Tools

Introduction

• Measurement transferring tools are tools that collect a

measurement, but do not have a scale to read the

measurement.

• Common tools are:

– Spring calipers

– Dividers

– Telescoping gauges

– Ball gauges

Spring Calipers

• Spring calipers are used to transfer

measurements.

• Three types of spring calipers

– Outside

– Inside

– Hermaphrodite

Dividers

• Dividers are very useful for laying

out several equal distances or

transferring a distance

measurement when other

measuring devices cannot be

used.

Telescoping gages

• Telescoping gages are used to

measure inside diameters.

• One or both ends are spring

loaded so they can be retracted

and inserted into the hole being

measured.

• The measurement is made with

a caliper or micrometer.

Ball Gauges

• Ball gauges are use to transfer

measurements that are too small for

telescoping gauges.

• The ball is split and a tapered wedge is

used to increase and decrease the

diameter of the ball halves.

The End