The document explains various modern gear generation processes, focusing on how involute gear teeth are produced. It details techniques such as gear milling, gear planing, gear shaping, and gear hobbing, highlighting their respective methodologies, applications, and efficiency. Gear hobbing is noted as the most productive method, while gear milling is limited to small batch production due to its slow pace.

1. Gear Generation process

2. Conventional Gear Genaration
Modern gear teeth have an involute profile.
These gear teeth are mostly made by the
following processes:
• Forming the gear teeth by using Milling.
• Generating the gear teeth by Gear planing or
rack.
• Generating the gear teeth by Gear shaping.
• Generating the gear teeth by gear Hobbing.

3. Gear Milling
• A involute form-milling cutter, which has the the
profile of the space between the gears, is used to
remove the material between the teeth from the
gear blank on a horizontal milling machine.
• The depth of cut into the gear blank depends on
the cutter strength, set-up rigidity and
machineability of the gear blank material.
• Milling is a form-cutting process limited to
making single gears for prototype or very small
batches of gears as it is a very slow and
uneconomical method of production.

4. Gear Milling

5. Gear Milling

6. Gear Planing or Rack Generation
• This is used for mid volume production. A rack,
which may be considered to be a gear of infinite
radius, is used as the cutter.
• It is constructed of hardened steel with cutting
edges round the teeth boundaries.
• The rack which is given a reciprocal laterial
motion equal to the pitch line velocity of the gear
is slowly fed to the slowly rotating gear blank.
• In this way, the material between the teeth is
removed and the involute teeth are generated.

7. Rack Generation

8. Gear Generating
Fig : (a) Producing gear teeth on a blank by form cutting. (b) Schematic illustration of gear generating with a
pinion-shaped gear cutter. (c) Schematic illustration of gear generating in a gear shaper using a pinion-
shaped cutter. Note that the cutter reciprocates vertically. (d) Gear generating with rack-shaped cutter.

9. Gear Shaping
• The cutter is a circular pinion-shaped cutter with
the necessary rake angles to cut.
• Both the gear blank and cutter are set in a vertical
plane and rotated such as that the two are like
gears in mesh.
• Gear shaping is faster than gear planing because
the cutting process is continuous and the cutter
does not have to be stepped back.
• This is the most versatile gear cutting process
which could produce internal and external gears,
close-coupled cluster gears and splines too.

10. Gear Shaping

11. Gear Hobbing
• The hob is used to generate the involute teeth.
• The hob is basically a straight cylindrical tool
around which a thread with the same cross
section as the rack tooth has been helically
wound.
• This hob is then rotated with the gear blank fed
onto the hob according to the depth of cut. The
helix pattern of hob as it rotates is the same as
that of the rack moving
• This is the most productive of all the gear
production processes.
• It cannot be used to cut internal gears.

12. Gear Hobbing

13. Gear Cutting with a Hob
Fig : Schematic illustration of
three views of gear cutting
with a hob.

14. Cutting Bevel Gears
Fig : (a) Cutting a straight bevel-gear blank with two cutters. (b) Cutting a spiral bevel gear
with a single cutter.

15. Gear Grinding
Fig : Finishing gears by grinding: (a) form grinding with shaped grinding wheels; (b) grinding by
generating with two wheels.