Practical Mechanical Maintenance Manual — Operation and Application of Tools

Practical Mechanical Maintenance Manual — Operation and Application of Tools

Table of content.

Purpose

To learn the operation and application of pipe wrenches, spanners, vernier calipers, micrometers, and feeler gauges.

 

 

I. Spanners

  1. Attention must be paid to incorrect selection of screwdrivers or improper application of force. This tool is used for tightening or loosening nuts and bolts. It may be a single-ended or double-ended wrench, or a ring spanner, with one end completely enclosed in a hexagonal or square shape. This eliminates the possibility of slipping.

  2. A socket wrench or socket may also provide greater… A pipe wrench is used for connecting conduit piping.

 

 

II. Vernier Caliper

  1. The vernier caliper consists of two mutually guided steel scales: one called the main scale and the other called the vernier scale. The main scale is engraved on an L-shaped frame that contains a fixed jaw and measuring head.

  2. The vernier scale slides along the main scale and contains a movable jaw and measuring head. When the two measuring faces are in contact, the reading should be zero. It is designed for measuring both internal and external features.

(1) Understanding the Vernier Caliper — Types and Accuracy

A “vernier caliper” can measure internal diameter, external diameter, center distance, width, length, etc.

Measurement ranges include:
 0–125mm, 0–150mm, 0–200mm, 0–300mm, 0–500mm, 0–1000mm.

By reading type:

  • Ordinary vernier caliper (a)

  • Electronic digital caliper (b)

  • Dial caliper (c)


By measurement type:

  • Vernier depth caliper

  • Vernier caliper

  • Height vernier caliper
     (as shown in Figure 1-3)

By measurement accuracy:

  • Ordinary vernier calipers: 0.02mm, 0.05mm, 0.1mm

  • Digital and dial calipers: 0.01mm

(2) Structure Names of Vernier Caliper (Figure 1-3)

(Figure 1-3)

(3) Principle of Vernier Scale Graduation

Vernier calipers have three common accuracies: 0.02mm, 0.05mm, 0.1mm.
 Taking the 0.02mm caliper as an example:

Figure 1-4 — 0.02mm Vernier Caliper Graduation Principle

Each small division on the main scale equals 1mm. When the two jaws are closed, 50 divisions on the vernier equal 49mm on the main scale.

Therefore:

49mm ÷ 50 = 0.98mm

Difference per division = 1mm − 0.98mm = 0.02mm

This is the accuracy value of the vernier caliper.

(4) Reading Method (Figure 1-5)

Figure 1-5 How to read a vernier caliper

  1. Read the whole millimeter value on the main scale to the left of the vernier zero line.

  2. Find the vernier line that aligns with a main scale line and read its decimal value.

  3. Add the integer value from the main scale and the decimal value from the vernier to obtain the measurement.

(5) Precautions for Using a Vernier Caliper

  1. Suitable for IT10~IT16 tolerance grade workpieces. Do not measure castings, forgings, or moving parts.

  2. Clean the measuring faces before use and check zero accuracy. Correct any zero error.

  3. Open jaws slightly larger than measured dimension. Keep fixed jaw steady; gently slide movable jaw. Apply moderate pressure. The measurement line should be perpendicular to the measured surface (Figure 1-6). Lock the screw.

  4. Read under bright light with line of sight perpendicular to scale.

  5. Keep away from strong magnetic fields. Oil after use and store in case.

The movement of the measuring jaws during measurement

Incorrect contact between the measuring surface of the vernier caliper and the workpiece

Figure 1-6 Precautions for using vernier calipers

Additional guidelines:
 6. For external diameter, jaws should extend beyond diameter; gently swing movable jaw and take minimum value.
 7. For internal diameter, gently swing and take maximum value.
 8. For depth measurement, keep caliper body perpendicular to surface.

 

 

III. Screwdriver

A commonly used tool for maintenance and assembly work. Many types exist. Improper pressure may damage screw head and screwdriver tip.

 

 

IV. Micrometer

  1. A highly useful instrument for measuring external dimensions with 0.01mm precision.

  2. Place workpiece between anvil and spindle. Rotate sleeve to clamp gently, tighten ratchet, then remove micrometer.

  3. Size is read from linear scale and thimble scale.

  4. Micrometers have different ranges. Keep clean and correct errors if any.

Micrometer (also called screw micrometer) is more precise than a vernier caliper. Accuracy: 0.01mm.

 

  • Outside micrometer

  • Depth micrometer

  • Inside micrometer

Structure (Figure 1-8)

Figure 1-8 Micrometer Structure Diagram

Graduation Principle

Pitch = 0.5mm
 Thimble has 50 divisions.
 0.5mm ÷ 50 = 0.01mm per division.

Reading Method (Figure 1-9)

  1. Read whole number on sleeve.

  2. Read half division (0.5mm if visible).

  3. Read thimble (n × 0.01mm).

  4. Add all values.

Figure 1-9

Precautions (Figure 1-10)

  1. Use ratchet for final tightening.

  2. Check half-millimeter line visibility.

  3. Do not ignore thousandths digit.

  4. Correct zero error if present.

Figure 1-10 Micrometer Measurement

Maintenance

  1. Check zero line.

  2. Clean measuring faces and workpiece.

  3. Use V-block for large workpieces.

  4. Use ratchet mechanism.

  5. Do not loosen back cover.

  6. Oil after use and store properly.

 

 

V. Dial Indicator

  1. Used to:
     a) Check shaft roundness
     b) Check parallelism
     c) Check flatness

  2. Small pressure transmitted via gear train to pointer.

  3. Used in printing to check roller parallelism.

  4. One full rotation = 1mm; divided into 100 divisions = 0.01mm precision.

Dial indicator and test indicator (Figure 1-14).
 Test indicator precision: 0.001mm
 Dial indicator precision: 0.01mm

Figure 1-14 Dial indicator and magnetic base

Structure (Figure 1-15)

Reading

Read small pointer (mm) + large pointer × 0.01mm.

Applications

  • Radial runout (Figure 1-16)

  • Straightness & parallelism (Figure 1-17)

Precautions

  • Check smooth movement

  • Secure mounting

  • Do not exceed range

  • Keep measuring rod perpendicular

  • Set pointer to zero before use

  • Avoid sudden impact

  • Apply initial preload 0.3–1mm

Correct

No-correct

 

VI. Feeler Gauge

Used to check clearance between mating surfaces.

Steel blades thickness range: 0.02mm to 1.00mm (Figure 1-19).

       Figure 1-19                                                          Figure 1-20

Usage (Figure 1-20)

Insert appropriate blade(s).
 Example:
 0.03mm fits, 0.04mm does not → gap is 0.03–0.04mm.

Common thicknesses:
 0.02mm, 0.03mm, 0.04mm, 0.05mm, 0.06mm, 0.07mm, 0.08mm, 0.09mm, 0.10mm, 0.15mm, 0.20mm, 0.25mm, 0.30mm, 0.35mm, 0.40mm, 0.45mm, 0.50mm, 0.75mm, 1.00mm

More blades combined → larger error. Not recommended to combine more than 5.

Precautions

A) Use minimum number of blades
 B) Do not force
 C) Do not measure hot workpieces
 D) In large surfaces, insertion length ≥ 20mm

 

 

Conclusion

Through this manual, we understand the operation and application of pipe wrenches, spanners, vernier calipers, micrometers, dial indicators, and feeler gauges.

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