The document discusses various methods for manufacturing gears, including: - Gear shaping and hobbing are generating processes that use rotating cutters to form gear teeth profiles. Gear shaping can produce external and internal spur gears with high accuracy, while hobbing is used for external spur gears and worm wheels. - Gear milling uses form cutters but requires indexing after each tooth, resulting in lower productivity and accuracy than generating processes. - Other methods discussed include broaching, rolling, powder metallurgy, casting, and machining smaller gears using EDM or broaching. Finishing processes like grinding, lapping, and burnishing are used to improve gear properties.

1. Gear Manufacturing
By S K Mondal

2. Manufacture of Gears
Manufacture of gears needs several processing operations in
sequential stages depending upon the material and type of the
gears and quality desired. Those stages generally are:
 Preforming the blank without or with teeth
 Annealing of the blank, if required, as in case of forged or
cast steels
 Preparation of the gear blank to the required dimensions
by machining
 Producing teeth or finishing the preformed teeth by
machining
 Full or surface hardening of the machined gear (teeth), if
required
 Finishing teeth, if required, by shaving, grinding etc
 Inspection of the finished gears

3. Forming and Generation
Gear teeth are produced by machining based on
Forming – where the profile of the teeth are obtained as
the replica of the form of the cutting tool (edge); e.g.,
milling, broaching etc.
Generation – where the complicated tooth profile are
provided by much simpler form cutting tool (edges)
through rolling type, tool – work motions, e.g., hobbing,
gear shaping etc.

5. Sunderland method using rack type cutter
 The rack type HSS cutter (having rake and
clearance angles) reciprocates to accomplish the
machining (cutting) action while rolling type
interaction with the gear blank like a pair of rack
and pinion.
External gear teeth generation by rack type cutter (Sunderland method)

6. Sunderland method using rack type cutter
 Applications of this method (and machine) include:
 Moderate size straight and helical toothed external
spur gears with high accuracy and finish
 Cutting the teeth of double helical or herringbone
gears with a central recess (groove)
 Cutting teeth of straight or helical fluted cluster gears
 However this method needs, though automatic, few
indexing operations.

7. Gear shaping
 Gear shaping is similar to the rack type cutting process,
excepting that, the linear type rack cutter is replaced by a
circular cutter where both the cutter and the blank
rotate as a pair of spur gears in addition to the
reciprocation of the cutter.

8. Gear shaping
 Generation method is characterised by automatic indexing
and ability of a single cutter to cover the entire range of
number of teeth for a given combination of module and
pressure angle and hence provides high productivity and
economy.
 The gear type cutter is made of HSS and possesses proper
rake and clearance angles.
 The additional advantages of gear shaping over rack type
cutting are:
 Separate indexing is not required at all
 Straight or helical teeth of both external and internal
spur gears can be produced with high accuracy and
finish
 Productivity is also higher.

9. Gear Hobbing
 The HSS or carbide cutter having teeth like gear milling
cutter and the gear blank apparently interact like a pair
of worm and worm wheel.
 The hob (cutter) looks and behaves like a single or
multiple start worms.
(a) Straight (b) helical tooth and (c) worm wheel

10. Gear Hobbing
 Having lesser number (only three) of tool – work
motions, hobbing machines are much more rigid, strong
and productive than gear shaping machine.
 But hobbing provides lesser accuracy and finish and is
used only for cutting straight or helical teeth (single) of
external spur gears and worm wheels.

11. Advantages of Gear Hobbing
(a) The method is versatile and can generate spur,
helical, worm and worm wheels.
(b) Since gear hobbing is a continuous process, it is
rapid; economical and highly productive.
(c) The method produces accurate gears and is suitable
for medium and large batch production.
(d) The cutter is universal, because it can cut all gears of
same module, irrespective of number of teeth on the
gear.

12. Disadvantages of gear Hobbing
(a) Gear hobbing cannot generate internal gears and
bevel gears.
(b) Enough space has to be there in component
configuration for hob approach.
Applications of Hobbing
 The gears produced by gear hobbing are used in
automobiles, machine tools, various instruments, clocks
and other equipments.

13. Milling
 Gear teeth can be produced by both disc and end mill type
form milling cutter.
Fig. (a) disc type and end mill type for
(b) single helical and
(c) double helical teeth

14. Milling
Production of gear teeth by form milling are characterised
by:
 Use of HSS form milling cutters
 Use of ordinary milling machines
 Low production rate for
 Need of indexing after machining each tooth gap
 Slow speed and feed
 Low accuracy and surface finish
 Inventory problem – due to need of a set of eight cutters for
each module – pressure angle combination
 End mill type cutters are used for teeth of large gears and / or
module.

15. Shaping, Planning and Slotting
 Straight toothed spur gear can be produced in shaping
machine.
 Both productivity and product quality are very low in
this process which therefore, is used, if at all, for making
one or few teeth on one or two pieces of gears as and
when required for repair and maintenance purpose.
 Planning and slotting machines work on the same
principle. Planning machine is used for making teeth of
large gears whereas slotting for internal gears.

16. Fig- gear teeth cutting in ordinary shaping machine

17. Fast production of teeth of spur gears
Parallel multiple teeth
shaping
 It is similar to ordinary
shaping but all the tooth gaps
are made simultaneously,
without requiring indexing,
by a set of radially in feeding
single point form tools.
 This old process was highly
productive but became almost
obsolete for very high initial
and running costs.

18. Fast production of teeth of spur gears
Broaching
 Teeth of small internal and external spur gears; straight
or single helical, of relatively softer materials are
produced in large quantity by broaching.
 This method leads to very high productivity and quality
but cost of machine and broach are very high.

19. Manufacture of gears by rolling
 The straight and helical teeth of disc or rod type external
steel gears of small to medium diameter and module are
generated by cold rolling by either flat dies or circular
dies.
 Such rolling imparts high accuracy and surface integrity
of the teeth which are formed by material flow unlike
cutting.
 Gear rolling is reasonably employed for high productivity
and high quality though initial machinery costs are
relatively high.
 Larger size gears are formed by hot rolling and then
finished by machining.

21. Powder Metallurgy
 Small size high quality external or internal spur, bevel or
spiral gears are also produced by powder metallurgy
process.
 Large size gears are rolled after briquetting and sintering
for more strength and life.
 Powder metallurgically produced gears hardly require
any further finishing work.

22. Wire EDM
 Geometrically accurate but moderately finished straight
toothed metallic spur gears, both external and internal
type, can be produced by wire type Electro-discharge
Machining (EDM).

24.  Blanking in Press tool
 Plastic moulding
 Extrusion process

25. Casting
 Sand casting
 Metal mould casting
 Die casting
 Investment casting
 Shell mould casting
 Centrifugal casting

27. Gear finishing process
 One of the goals of the gear finishing process in gears is
to obtain a certain level of toughness in the gear teeth to
reduce and/or eliminate bending and contact fatigue
failures.
 Reduction of index undulation errors associated with
helical gear teeth caused by the grinding process during
the manufacture of the gears without degrading other
gear accuracies (e.g. profile, tooth spacing) below levels
required for precision (AGMA16 or DIN1) gears.
 A mold of the space between several gear teeth is
obtained, with the mold having a length equal to or
greater than the wavelength of the undulation error to be
reduced.

28.  A micro finishing film is affixed to the mold and the
mold is placed relative to a gear tooth so that the micro
finishing film rests against a tooth surface having the
undulation error.
 The grit size of the micro finishing film is such as to
remove approximately 2 to 3 millionths of gear material
with each pass through the teeth by the mold. Multiple
passes are made by hand until the undulation error is
reduced to an acceptable value. During the process the
micro finishing film is replaced after approximately 3 or
4 passes and the process is repeated for each tooth of the
gear.

29. Gear shaving
 Gear shaving is a gear finishing operation with high
efficiency and high precision.
 When a work gear has been shaved by a shaving cutter
with a true involute profile, the ''mid-concave''
phenomena inevitably exist around the pitch points of
the work gear tooth flanks.
 Aiming at this problem, a new-style shaving cutter with
unequal depth gashes is designed and manufactured.
 This paper analyses the forming of the gash on the basis
of the slotting principle, and proposes a gash-designing
method.
 Experiment has proven that the shaved gear has a better
surface finish that achieves the anticipated effect.

30. Gear burnishing
 It is designed to remove or reduce gear tooth nicks and
burrs, along with improving the smoothness of the
tooth's active profile finish.
 The action of the burnishing dies on the tooth surface
allows the machine to accomplish these quality
improvements without altering the tooth profile or lead.
 Both internal and external gears are possible to burnish.

31. Gear Lapping
 Gear lapping is used to finish hardened gears by
correcting small errors in spacing, profile, helix
angle, and eccentricity.
 The operation is performed with all forms of gears
running together with mating gears, and cast iron
toothed laps, under a flow of fine oil mixed with
an abrasive compound.

32. IES - 1992
Gear lapping
(a) An operation after heat treatment
(b) An operation prior to heat treatment
(c) An independent operation for gear reconditioning
(d) None of the above

33. IES - 1999
Consider the following processes for the
manufacture of gears:
1. Casting
2. Powder metallurgy
3. Machining from bar stock
4. Closed die forging
The correct sequence in increasing order of bending
strength of gear teeth is
(a) 1, 2, 3, 4 (b) 1, 2, 4, 3
(c) 2, 1, 4, 3 (d) 2, 1, 3, 4

34. IES - 2006
Which of the following is/are used for cutting
internal gears?
1. Gear hobber 2. Gear shaper
3. Rack cutter 4. Jig borer
Select the correct answer using the codes given below:
(a) Only 1 and 2 (b) Only 2 and 3
(c) Only 1 and 4 (d) Only 2

35. IES - 2005
In helical milling, the ratio of the circumference of
the gear blank to the lead of the helix determines
the:
(a) Proper speed to use
(b) Proper feed and depth of cut required
(c) Angle setting of the machine table
(d) Gear ratio for table screw and dividing head

36. IES 2010
Match List I with List II and select the correct answer using
the code given below the lists:
List I List II
(Type of work) (Manufacturing)
A. High rate production of worm Gears and 1. Gear shaving
worm wheel
B. Generating internal gears and Cluster gears 2. Gear milling
C. Finishing of gear tooth profiles 3. Gear hobbing
D. Repair and piece production of gears 4. Gear shaping
A B C D A B C D
(a) 2 1 4 3 (b) 3 1 4 2
(c) 2 4 1 3 (d) 3 4 1 2

37. IES - 1996
Gear cutting on a milling machine using an involute
profile cutter is a
(a) Gear forming process
(b) Gear generating process.
(c) Gear shaping process
(d) Highly accurate gear producing process.

38. IES - 2000
Which one of the following processes of gear
manufacture results in best accuracy of the involute
gear tooth profile?
(a) Milling
(b) Hobbing
(c) Rotary gear shaper
(d) Rack type gear shaper

39. IES - 2009
Assertion (A): Gears produced by employing form-
cutting principle using gear-milling cutter on a milling
machine are not very accurate.
Reason (R): Production of the correct gear tooth profile
employing form-cutting principle would require a
separate cutter for cutting different numbers of teeth
even for the same module and also errors are associated
with inaccurate operation of indexing mechanism.
(a) Both A and R are true and R is the correct explanation of
A
(b) Both A and R are true but R is NOT the correct
explanation of A
(c) A is true but R is false
(d) A is false but R is true

40. IES - 1996
Consider the following processes of gear
manufacture:
1. Milling with form cutter
2. Rack type gear shaper (gear planer)
3. Rotary gear shaper (gear shaper)
4. Gear hobbing
The correct sequence of these processes in increasing
order of accuracy of involute profile of the gear
(a) 3, 2, 4, 1 (b) 2, 3, 4, 1
(c) 3, 2, 1, 4 (d) 2, 3, 1, 4

41. IES - 2009
By which one of the following machines the teeth of
an internal spur gear can be cut accurately?
(a) Milling machine
(b) Slotting machine
(c) Hobbing machine
(d) Gear-shaping machine

42. IES - 2004
Gear shaping is a process of manufacturing gears.
Which one of the following principles is employed by it?
(a) Form cutting with cutter
(b) Generating tooth form with a reciprocating cutter
(c) Generating tooth form by a rotating cutter
(d) Generating form with a reciprocating and revolving
cutter

43. IES - 1992
In gear hobbing
(a) Only hob rotates
(b) Only gear blank rotates
(c) Both hob and gear blank rotate
(d) Neither hob nor gear blank rotates

44. IES - 2003
A spur gear of 40 teeth is machined in a gear
hobbing machine using a double start hob cutter.
The speed ratio between the hob and the blank is
(a) 1:20 (b) 1:40
(c) 40: 1 (d) 20: 1

45. IES - 2008
Which machining processes are used for gear
manufacture?
1. Form milling 2. Broaching
3. Roll forming 4. Hobbing
Select the correct answer using the code given below:
(a) 1, 2 and 3 (b) 1, 3 and 4
(c) 1, 2 and 4 (d) 2, 3 and 4

46. IES - 1999
A 60-teeth gear when hobbed on a differential
hobber with a two-start hob, the index change gear
ratio is governed by which one of the following
kinematic balance equations?
(a) 1 revolution of gear blank = 1/60 of hob revolutions
(b) 1 revolution of gear blank = 2/60 of hob revolutions
(c) 1 revolution of hob = 2/60 of blank revolutions
(d) 1 revolution of hob = 1/60 of blank revolutions

47. IES - 1997
Which of the following motions are not needed for
spur gear cutting with a hob?
1. Rotary motion of hob
2. Linear axial reciprocator motion of hob
3. Rotary motion of gear blank
4. Radial advancement of hob.
Select the correct answer using the codes given below:
(a) 1, 2 and 3 (b) 1, 3 and 4
(c) 1, 2 and 4 (d) 2, 3 and 4

48. IES - 2007
Which of the following methods are gear generating
processes?
1. Gear shaping
2. Gear hobbing
3. Gear milling
Select the correct answer using the code given below:
(a) 1, 2 and 3 (b) 1 and 2 only
(c) 2 and 3 only (d) 1 and 3 only

49. GATE – 2007 (PI)
Which one of the following gear manufacturing
processes is NOT based on generation principle?
(a) Gear Hobbing (b) Gear Shaping
(c) Gear Milling (d) Gear Shaving

50. IES - 1993
Internal gear cutting operation can be performed by
(a) Milling
(b) Shaping with rack cutter
(c) Shaping with pinion cutter
(d) Hobbing

51. GATE-2016
Internal gears are manufactured by
(a) Hobbing
(b) Shaping with pinion cutter
(c) Shaping with rack cutter
(d) Milling

52. IAS - 1998
Assertion (A): Internal gears are cut on a gear
shaper.
Reason (R): Hobbing is not suitable for cutting
internal gear.
(a) Both A and R are individually true and R is the
correct explanation of A
(b) Both A and R are individually true but R is not the
correct explanation of A
(c) A is true but R is false
(d) A is false but R is true

53. IES - 2006
Which of the following cannot be cut by hobbing
process?
(a) Helical gears (b) Bevel gears
(c) Worm gears (d) Spur gears

54. IES - 1996
For the manufacture of full depth spur gear by
hobbing process, the number of teeth to be cut = 30,
module = 3 mm and pressure angle = 20°. The radial
depth of cut to be employed should be equal to
(a) 3.75 mm (b) 4.50 mm
(c) 6.00 mm (d) 6.75 mm

55. IES - 1995
While cutting helical gears on a non-differential
gear hobber, the feed change gear ratio is
(a) Independent of index change gear ratio
(b) dependent on speed change gear ratio
(c) Interrelated to index change gear ratio
(d) Independent of speed and index change gear ratio.

56. IES - 1992
Gear burnishing process for
(a) Removing residual stresses from teeth roots
(b) Surface finishing
(c) Under-cut gears
(d) Cycloidal gears

57. IAS - 2003
Which one of the following is not a feature of gear
hobbing process?
(a) High rate of production
(b) Generation of helical gears
(c) Very accurate tooth profile
(d) Generation of internal gears

58. IAS - 2001
Consider the following motions and setting in a
hobbing machine:
1. Hob rotation
2. Job rotation
3. Axial reciprocating hob rotation
4. Tilting of hob to its helix angle
Which of these motions and setting in a hobbing
machine are required to machine a spur gear?
(a) 1, 2 and 3 (b) 2, 3 and 4
(c) 1, 2 and 4 (d) 1, 3 and 4

59. IES - 1994
Consider the following machine tools:
1. Hobbing machine
2. Gear shaping machine
3. Broaching machine.
The teeth of internal spur gears can be cut in
(a) 1, 2 and 3 (b) 1 and 2
(c) 1and 3 (d) 2 and 3

60. GATE-2016 (PI)
A helical gear with involute tooth profile has been
machined with a disc-type form gear milling cutter. The
helical gear has 30 teeth and a helix angle of 30o. The
module of the gear milling cutter is 2. The pitch circle
diameter (in mm) of the helical gear is_______________.