The mechanical metrology is a subject which is studying about how to measure the length or meter. These will show all the tools, how to measurement, noticeable using tools in minimizing placement.

1. Chapter II: Engineering Metrology
and Instrumentation
មាត្រសាត្្ត​មេកានិច
Prepared by: Sry Vannei

2. I. Line-Graduated Instruments:
I. Linear Measurements (Direct Reading):
I. a. Rules:
Rules, sometimes called line gauge, is an
instrument used in geometry, technical drawing,
printing and engineering (building to measure
distances or to rule straight lines).
Type of the rulers:
- Wood rulers
- Plastic rulers
- Metal rulers
2

3. Wooden carpenter's rule (16th
century)
Plastic rulers

4. Ruler in measurement:
Here are two rulers that we use in the
mechanical measuring:
- Steel rule, bar or tape measure (Mètre-ruban)
have length from 0.2 to 7 m. Precision: 1 mm.
- Combination Square Rule has length of 0.2
m, 0.5 m, 2 or 3 m. Precision: 0.1mm.

5. I. b. Vernier Calipers (Pied à coulisse):
 Principal of vernier linear :
Vernier came from the named for P. Vernier, who lived
in 1600s. Vernier calipers have a graduated beam and a
sliding jaw with a verneir. These instruments are also
called CALIPER GAGES. The two jaws of the caliper
contact the part being measured, and the dimension is
read at the matching graduated lines. Caliper gages
have different precision, 1/10 (0.1mm) or 1/20 (0.05mm)
or 1/50 (0.02mm). Ex. On verneir sclae1/10, 9 mm of
graduated beam (fix scale) is divided by 10 parts equal.
Each verneir division measures 9/10 mm. The different
between them is 1mm-9/10mm = 1/10 mm.
5

6. Parts of a vernier caliper:
1. Outside jaws: used to measure external diameter or width of an object
2. Inside jaws: used to measure internal diameter of an object
3. Depth probe: used to measure depths of an object or a hole
4. Main scale: scale marked every mm
5. Main scale: scale marked in inches and fractions
6. Vernier gives interpolated measurements to 1/10 mm or better
7. Vernier gives interpolated measurements in fractions of an inch
8. Retainer: used to block movable part to allow the easy transferring of a
measurement
Parts

7. Reading:

8. Reading:
• To find x, find the mark on the Vernier scale which most nearly coincides
with a mark on the main scale. In figure 3 it is obviously the third mark.
• Now, it is clear that ............x = d - d’
• Remembering that each division on the main scale is 1mm and that each
division on the Vernier scale is 0·9mm, we have:
x = 3mm - 3(0·9)mm = 3(0·1)mm
Thus, the reading in this example is 12.3mm.

9. Reading:
Thus, the reading in this example is 16mm + 5x0.05mm = 16.25mm.
(scale 1/20 or 0.05mm)
Or 16mm + 2.5/10 mm = 16.25 mm.
5 divisions
16 mm

10.  Mode of utilization of Vernier calipers:
• Measuring the internal diameter of a hollow
cylinder
• Measuring the external diameter of a hollow
cylinder
• Measuring the depth of a hole in a piece of
metal
 Different types of Vernier calipers:
• Dial caliper
• Depth and adjust caliper
• Digital caliper

11. Dial
caliper
Depth and adjust caliper
Digital caliper

12. I. c. Micrometer
Commonly used for measuring the thickness
and inside or outside dimensions of parts.
The circumferential vernier reading to a
sensitivity of 0.01mm to 0.001mm can be
obtained with a micrometer. Micrometers are
also available for measuring depths
(micrometer depth gage) and internal
diameter (inside micrometer) with the same
sensitivity.

13.  Basic types of Micrometer:
• Outside micrometer: Typically use to measure
the wires, spheres, shafts, and blocks.
• Inside micrometer: Used to measure inside
diameter of the holes.
• Depth micrometer: Measure depth of slots and
steps.
 Operating Principle:
Micrometer uses the principle of screw to amplify
small distances that are too small to measure
directly into the large rotation of screw that are big
enough to read from a scale. The accuracy of it
derives from the accuracy of thread form that is at
its heart.

14. Outside micrometer :
Parts:
A micrometer consist of :

15. Reading:
The spindle of an ordinary metric micrometer has 2
threads per millimeter, and thus one complete
revolution moves the spindle through a distance of
0.5 mm. The longitudinal line on the frame is
graduated with 1 mm divisions and 0.5mm
subdivisions. The thimble has 50 graduations,
each being 0.01mm . Thus, reading is given by the
number of millimeter divisions visible on the scale
of the sleeve plus the particular division on the
thimble which coincides with the axial line on the
sleeve plus subdivision 0.5 if visible.

16. Ex. Suppose that the thimble were screw out so that graduation 5,
and one additional subdivision were visible, and that graduation 28 on
the thimble coincide with the axial line on sleeve. Thus, the reading
then would be 5.00 + 0.5+ 0.28 = 5.78mm.

17. Inside micrometer : Precision: 0.01mm.
Depth micrometer: Precision: 0.01mm.

18. II. Angle-Measuring Instruments:
 Universal Bevel Protractor: (first
design in 17th century)
For measuring angle with ±0.01 degree.

19. Parts:
A protractor is a device for measuring angle between two intersection lines.
The angle is measured in degree, and circle is defined as having 3600 of
identical size. The main component of the bevel protractor is the main scale
which is numbered to read from 0 to 900 and then back from 900 to 0. A
minute of arc, arcminute, or minute of angle (MOA, arcmin, amin, am ) (’ call
prime) = 1/60degree. 1 arcsecond (arcsec, asec, as) (’’ call double prime)=
1/60 arcminute.
The universal bevel protractor is capable of measuring to within 5 min or 1/120

20. Reading:
As with other vernier measuring devices, the vernier scale of the bevel
protractor allows the tool to divide each degree into smaller increments. The
vernier scale is divided into 24 spaces, 12 spaces on either side of the zero.
Each space on the vernier scale is 1/120 is equal to 5’. To read the
protractor, note where zero on the vernier scale line up with the degree on
the dial in fig. below. The degree are read directly from the main scale. Zero
on the vernier main scale is just passed the 850 mark. Now, reading in the
same direction (counter-clockwise), count, from zero on the vernier scale to
the lines that match up on the dial. Thus, the total number is 85030’.
Always read the vernier in the same direction that you read the dial

21. Types:
• Bevel protractor optic
• Bevel protractor digital

22. III. Linear Measurement (Indirect Reading):
Indirect-reading instruments are typically
CALIPERS and dividers without any graduated
scales. They are used to transfer the measured
size to a direct-reading instrument, such as a rule.
After, adjusting the legs to contact the part at the
desired location, the instrument is held against a
graduated rule, and the dimension is read.
Because of the experience required to use them
and their dependence on graduated scales, the
accuracy of indirect measurement tools is limited.
Telescoping gages can be used for indirect
measurement of holes.

23. IV. Dial Indicators:
Dial indicators are simple mechanical device that convert linear
displacements of a pointer to the amount of rotation of an indicator
on a circular dial. The indicator is set to zero at a certain reference
surface, and the instrument or the surface to be measured (either
external or internal) is brought into contact with the pointer. The
movement of the indicator is read directly on the circular dial (either
plus or minus) to accuracies as high as 1 µm.
Dial indicators of several design are available for use as portable
units. The basic design consists of a rack-and-pinion, a gear-train,
and rack-and-pinion with gear-train mechanism that, together,
convert linear motion to rotary motion, with large amplifications.

24. Types:
 Amplifier by gear train: The movement of ball tip
guide the gear train with the needle. There is a spiral
spring that pull the needle back. One rotation revolution
of needle equal to 1mm linear displacement. In the dial,
the graduation is divided into 100 parties equal. Each
division represent 1/100 mm of displacement of ball tip.
 Amplifier by rack-and-pinion : The main components
are the rack and pinion that convert linear motion to
rotary motion. The motion is transfer from the ball tip
follow by rack which pushes the needle move (1 division
is 0.002 mm). At the end the spring pull the needle back
to the original position.
 Amplifier by rack-and-pinion and gear train: The
combination of rack with gear train were used in this
amplification. The ball tip guide the gear train with the
needle to move (1division is 0.001mm).

25. Amplifier by gear train (0.01mm)

26. Amplifier by rack-and-pinion

27. Amplifier by rack-and-pinion and gear train

28. Utilization:
For obtain the correct measuring, the ballpoint neck is
perpendicular to the object surface of measuring.
 Direct measuring: It doesn’t use any reference gages block in
measuring.

29.  Indirect measuring: It uses gage blocks standard (Étalon)for
reference in measuring.

30.  Applications:
It uses in many applications such as:
 Control thickness
 Control length
 Control cylindrical
 Control profounder
 Control parallel