1. Measuring Tools

2. Introduction
Measuring tools for small engines are divided into three categories.
Direct reading
Measurement transferring
Reject gages

3. Direct Reading Measuring Tools
Small engines use two types of direct reading measuring tools:
Micrometers
Calipers

4. Micrometers

5. Micrometer Introduction
A micrometer is a mechanical device designed to measure distances as small as 1/10,000 of an inch ( 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:
Micrometer caliper
Inside micrometer
Depth gauge micrometer
Micrometer calipers are available in mechanical and digital models.

6. 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.

7. 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..

8. 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.

9. 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).

10. 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 inch.

11. Micrometer Caliper Example
Determine the reading for the micrometer caliper in the illustration.
Smallest whole unit 0.000
Tenths of an inch 0.300
Twenty five thousands ( x 2 ) 0.050
Thousands 0.015
Sum (measurement) 0.365

12. 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

13. 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.

14. 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

15. Inside Micrometer Example 2
Inside micrometers use extensions to change the range of measurements.
Adding an extension increases the minimum measurement.
In this example a 1/2 inch extension has been added.
Smallest whole unit 2.000
Tenths 0.200
Twenty five thousands 0.075
Thousands 0.001
Reading 2.276
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.

16. 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

17. Depth Gauge Micrometer Example
Read the depth gauge micrometer in the illustration
Smallest whole unit 0.000
Tenths 0.800
Twenty Five Thousands 0.050
Thousands 0.017
Sum (reading) 0.867

18. Calipers

19. 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

20. 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.

21. Vernier Scale
A Vernier is a mechanical means of magnifying the last segment on the main scale so addition subdivisions can be made.
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.

22. Vernier Caliper-practice
Read the Vernier caliper in the illustration.
LOC
Smallest whole unit 1.000
Tenths of an inch 0.200
Twenty five thousands
Vernier scale 0.011
Sum (measurement) 1.211

23. Dial Caliper A dial replaces the Vernier.
This makes the caliper easier to read.
The reader must still determine the units and graduations.

24. Measurement Transferring Tools

25. 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

26. Spring Calipers Spring calipers are used to transfer measurements.
Three types of spring calipers
Outside
Inside
Hermaphrodite

27. Dividers
Dividers are very useful for laying out several equal distances or transferring a distance measurement when other measuring devices cannot be used.

28. 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.

29. 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.

30. The End