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1. BASIC MECHANICAL ENGINEERING
Presented to:
Prof. Akbar Ali Qureshi
Presented by:
Group 1
Group Leader:
Memoona Javed (2022-EE-33)
Group Members:
Laraib Khan(2022-EE-10)
Shah Riyan(2022-EE-17)
Usman Ali(2022-EE-20)
Zain Tariq(2022-EE-15)

3. Gear:
 A Gear is a wheel with teeth that mesh together with other
gears.
 The teeth on the two meshing gears all have the same
shape.
 Gears can change:
 Speed
 Torque
 Direction
of rotating axels

4. Functions of Gears:
 Ensure positive motion.
 Reverse direction of rotation.
 Change the torque.
 Move rotational motion to different axis.
 Increase or decrease the speed of rotation.
 Keep the rotation of two axis synchronized.
 Change the direction of power source.

5. Terms:
 Pinion: Smaller of the pair of gears.
 External Gear: Teeth formed on the outer surface of a
cylinder.
 Internal Gear: Teeth formed on the inner surface of a
cylinder.

6. Types of Gears
Following are the different types of gears :
 Spur Gear
 Helical Gear
 Rack and pinion Gear
 Bevel Gear
 Worm and Worm Gear

7. Spur Gear
• Most common.
• Move opposite to each other.
• Used to transmit power from one shaft to another parallel
shaft.
• Driver gear is the gear connected to motor.
• Used in electric screwdriver,
oscillating sprinkler, windup
alarm clock, washing machine
and clothes dryer.

8. External Spur Gear:
 In external gearing, the gears of the two shafts mesh
externally with each other which is shown in figure. The
larger of these two wheels is called spur wheel or gear and
the smaller wheel is call pinion.

9. Internal Spur Gear:
 In internal spur gearing, the gears of these two shafts mesh
internally with each other as shown in figure. The larger of
these two wheel is called annular and smaller wheel is
called pinion.

10. Spur Gear
Advantages:
• Low manufacturing cost.
• Simple design.
• Ease of maintenance.
Disadvantages:
• Less load capacity.
• Higher noise level.

11. Bevel Gear
 Used when two axis intersect at right angles.
 Changes the direction of drive.
 They are usually mounted on shafts that are 90 degrees
apart, but can be designed to work at other angles as well.
 The teeth on bevel gears can be straight or spiral.

12. Disadvantages:
Used:
•Hand drills.
•Automobiles
•Printing presses
•Power plants
•Steel plants etc.
•Gears are designed to work specifically with
each other not interchangeable.
•Must be precise mounted.
Bevel Gear

13. Helical Gears
 The teeth on helical gears are cut at an angle to the face of
the gear.
 This gradual engagements makes helical gears operate
much more smoothly and quietly than spur gears.
 Helical gears can be meshed in parallel or crossed
orientations.

14. Herringbone Gears
 A herringbone gear is a specific type of double helical gear,
which is side to side (not face to face) combination of the
two helical gears of opposite hands.
 Herringbone gears are mostly used on heavy machinery.

15. Rack and Pinion Gears
 Pinion is the round gear and Rack is the flat straight piece.
 Torque can be converted to linear force by meshing a rack
with a pinion: pinion turns; rack moves in a straight line.
 This mechanism is used in steering wheels of automobiles.

16. Worm Gears
 Worm gears are used when large gear reduction are needed. It is
common for worm gears to have reductions of 20:1, and even up to 300:1
or greater.
 Many worms gears have an interesting property that no other gear set
has the worm can easily turn the gear, but the gear cannot turn the
worm.
 Used:
• Material handling
• Transportation machinery
• Machinery tools
• Automobiles etc.

17. Sprocket
 Two gears that don`t touch each other.
 Driven by a chain.
 Both sprockets rotate in the same direction.

18. Sprocket
 Example:
• Bikes
• Machinery.
• Motorcycles.
• Tracked vehicles.
• Film projectors.

19. Material
 Nonferrous alloys.
 Cast irons.
 Power metal.
 Plastics – commonly used when cost or weight is concern. A properly
designed plastic gear can replace steel in many cases because it has
many desirable properties:
 Steels are most commonly used because of their high strength-to-
weight ratio.
•Dirt tolerance
•Low speed meshing
•Ability to skip(Not needing additional lubrication)

20. Gear Ratios
 The gear ratio is the ratio of the number of teeth on
one gear to the number of teeth on the other gear.
 Gear ratio = 40 to 8 or, simply 5 to 1
 Ratio can be written as:
• a:b
• a to b
• a/b

21. Basic Rules of Gears
 If a gear gives more force gets less speed.
 If get more speed gets less force.
 Small gears driving large gear: Torque increases.
 Large gear driving small gear: Torque decreases.
 Small gear driving big gear: Speed decreases.
 Large gear driving small gear: Speed increases.

22. Velocity Ratio of Gear Drive
 Velocity Ratio = ω2 / ω1 = N2 / N1 = d1 / d2
d = Diameter of wheel
N = Speed of the wheel
ω = Angular Speed

23. Example Problem