Gears and gears types and gear making with diagrams

1. Gears & Gear Making

2. 2
Gear

3. 3
Gear
A gear is a Mechanical component used to
transmit power and motion
Key operations
Reversing the direction of rotation
Altering angular orientation of rotary motion
Convert rotary motion into linear motion &
vice versa
Altering speed ratios

4. 4
Characteristics
In geometry gears are
Toothed wheels
Transmit motion & power from one shaft to
another when they are closer to each other (not
too far apart)
Constant velocity ratio is desired
In comparison with belt, chain & friction
devices are : More compact
Operate at high speeds
Precise timing
Large power

5. 5
Characteristics (Contd)
Gears can mesh with any component having
compatible teeth
Gears of unequal (sizes) diameters can be
combined to produce mechanical advantage
Rotational speed & torque of second gear may
be different from that of the first

6. 6
In a set of gears, the smaller gear is called a
pinion
The larger gear is called a wheel or simply
gear
Characteristics(Contd)

7. 7
Classification
Gears are classified according to the relative
location of the axes of mating gear shafts
 Gears with parallel axes
• Spur gears
• Helical gears
• Herringbone gears
• Rack and pinion gears
• Internal gears
 Shaft axes intersect if prolonged
• Straight bevel gears
• Spiral bevel gears
 Shaft axes neither parallel nor intersecting
• Worm gears

8. 9
Gear Types
Spur gears
 Most common type
 Transfer power between parallel shafts
 Good mechanical efficiency
 Cheapest

9. 10
Gear Types
Helical gears
 Variation of spur gears
 Teeth are slanted at an angle
 Allowing more teeth coming in contact
with each other
 Wide load distribution
 Less noise

10. 11
Gear Types
Herringbone gears
 Double helical gears
 Can absorb axial thrust within the gears

11. 12
Gear Types
Rack & pinion arrangement
 Convert rotational motion into
translational motion

12. 13
Gear Types
Bevel gears
 Connect two intersecting shafts
 Making an angle with one another
 Slightly less efficient than spur gear
 More expensive
 Noisy at high speed

13. 14
Gear Types
Worm & worm gear
 Shafts are generally but not necessarily
at right angles in different planes
 Axes are orthogonal to each other but
not intersecting
 Expensive
 Efficiency drops off quickly as gear
ratio increases

14. 15
Gear Materials
Certain non ferrous alloys
Cast iron
Plastics (Teflon)
Steels (most common)
 High strength to weight ratio
 Low cost

15. 16
Nomenclature
Pitch circle
It is the circumference on which gear teeth
are developed (an imaginary circle)
Addendum
of a tooth is the radial distance from the
pitch circle to the outside diameter or
addendum circle

16. 17
Nomenclature

17. 18
Nomenclature(Contd)
Dedendum
of a teeth is the radial distance from the
pitch circle to the root or dedendum circle)
Diameteral pitch (P)
referred to as pitch of a gear, is the ratio of
the number of teeth (N) to the pitch
diameter (D) or P = N/D

18. 19
Nomenclature(Contd)
Circular pitch (p)
is the distance from a point on one teeth to
the corresponding point on an adjacent
tooth, measured on the pitch circle
p = πD/N and P = π/p
Gears & gear cutters are standardized
according to the diameteral pitch P
6-pitch (6P) gear has 6 teeth per inch of P

19. 20
Nomenclature(Contd)
Pressure angle (ф)
If a common tangent is drawn to the pitch
circles of two meshing gears then a line of
action (angle of thrust) is drawn at an
angle called pressure angle to this line
Usually the angle is 14.5° or 20° of the
gears

20. 21

21. 22
Nomenclature(Contd)
Module (M)
It is the metric standard for pitch
The length in mm that each tooth will
occupy if the teeth in the gear were
spaced along the pitch diameter

22. 23
Nomenclature(Contd)
Centre distance
It is the distance between centres of two
meshing gears
Backlash
When two gears are meshed together, the
slippage or play between the teeth of the
two gears is called backlash

23. 24
Nomenclature(Contd)
Involute gear profile
In an involute gear the profiles of the teeth
are involutes of a circle
where involute of a circle is the spiralling
curve traced by the end of an imaginary
taut string unwinding itself from that
stationary circle
In involute gear design all contact between
two gears occur in the same fixed flat
plane (the plane of action) even as their
teeth mesh in and out

24. 25
Involute gear profile

25. Involute Curve
26

26. 27
Involute gear profile

27. 28
Involute Gear Tooth Profile

28. p = πD/N and P = π/p

29. Diametral Pitch
30
Diametral pitch (P). This is the English
(inch) method for Specifying pitch, and P
is a number which represents the number
of teeth for each inch of reference
diameter. Thus If a gear has 60 teeth and
its reference diameter is 6 in, There are
60/6= 10 teeth for each inch of reference
diameter, signifying a diametral pitch of
10

30. 31
(Contd)

31. 32
Gear casting
Gear forming
Gear generating
Gear shaping
Gear cutting
Gear Planning
Gear Making Processes

32. Gear Manufacturing Procedure
For making gear, diameter and number of teeth
should be known. Dp number can be calculated
as:
Dp number = teeth + 2 / Diameter of gear
33

33. Procedure(Contd)
Index plate
For indexing there are three methods
1. Direct Indexing (24/n)
2. Plane Indexing (40/n)
3. Angular indexing (360/n)
For index plate, we will use plane indexing and if
we want to have 18 teeth (40/18 = 2-2/9). Hence
there are two turn of shaft, 2 holes & index
number is 9
34

34. 35
Gear shaving
Gear grinding
Gear lapping
Shot blasting
Sand Blasting
Phosphate coating
Gear Finishing Processes

35. 36
Gear casting (low melting point metals)
 Sand casting
 Die casting
 Investment casting
 Centrifugal casting
 Injection moulding (plastics)
Gear Making Processes

36. ©2002 John Wiley & Sons, Inc. M. P. Groover, “Fundamentals of Modern Manufacturing 2/e”
Steps in the production sequence in sand casting

37. ASSIGNMENT-2
38
 Describe different steps in Investment
casting and Die Casting
 Date of submission; Next week same
day
 Your Assignment should be hand
written with sketches