Gears and gear drives are used to transmit power or motion between two shafts. Common uses include situations where the center distance is short, speed needs to be increased or decreased, or high torque needs to be transmitted. The main types of gears are spur, helical, bevel, spiral, worm, rack and pinion, and internal/external gears. Spur gears are the simplest type but can be noisy. Helical gears are more expensive to produce but operate more quietly. Gear failures can damage an entire system so they require precision manufacturing.

1. GEARS AND GEAR DRIVES
• IT IS A TOOTHED WHEEL WITH TEETH CUT ON
ITS PHERIPHERY.
•POWER OR MOTION IS TRANSMITTED FROM ONE
SHAFT TO ANOTHER WITH GEAR DRIVE.
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2. WHEN GEAR DRIVES ARE USED?
1. CENTER DISTANCE ARE RELATIVELY SHORT
2. SPEED OF THE SHAFT IS LOW
3. POSITIVE DRIVE IS NECESSARY I.e VELOCITY
RATIO IS FIXED AND KNOWN WITH CERTAINTY
4. NEED TO STEP UP OR STEP DOWN THE SPEED
5. HIGH TORQUE IS TRANSMITTED
6. PRECISE TIMING IS REQUIRED
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3. DISADVANTAGES OF
GEAR DRIVES
1.
WHOLE SET IS EFFECTED IF ONE TOOTH GETS DAMAGED
2.
MANUFACTURING OF GEARS REQUIRES SPECIAL TOOLS
AND EQUIPMENT.
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4. TYPES OF GEARS
1.
2.
3.
4.
5.
6.
7.
SPUR GEAR
HELICAL GEAR
BEVEL GEAR
SPIRAL GEAR
WORM GEAR
RACK AND PINION
INTERNAL AND EXTERNAL GEARING
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5. SPUR GEAR
1. IT IS A CYLINDRICAL GEAR
2. TOOTH TRACES ARE STRAIGHT LINES AND
PARALLEL TO THE GEAR AXIS
3. USED FOR TRANSMITTING OF MOTION BETWEEN
TWO SHAFTS WHOSE AXIS ARE PARALLEL AND
COPLANAR
4. THESE GEARS HAVE HIGH (96-98%) EFFICIENCY
5. FREE FROM AXIAL THRUST DURING TOOTH
ENGAGEMENT.
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6. APPLICATIONS OF SPUR GEAR
•
USED AS A SLIDING GEARS FOR SPEED CHANGING
MECHANISM IN GEAR BOXES OF LATHE.
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7. DIS ADVANTAGE OF SPUR GEAR
1. MORE NOISY
2. WEAR OUT READILY
3. DEVELOP BACKLASH
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8. HELICAL GEAR
1. CYLINDRICAL GEAR TOOTH
2. TOOTH TRACES ARE STRAIGHT HELICES AND
INCLINED AT ANGLE TO THE GEAR AXIS.
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9. APPLICATIONS OF HELICAL GEAR
1. AUTOMOBILE GEAR BOXES
2. STEAM AND GAS TURBINE FOR SPEED
REDUCTION.
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10. 1.
BEVEL GEAR
BEVEL GEAR WHEELS CONFORM TO THE FRUSTA OF CONES HAVING
A COMMON VERTEX.
2.TOOTH TRACES ARE STRAIGHT LINE GENARATORS OF THE CONE.
3.USED CONNECT TWO SHAFTS WHOSE AXIS ARE
CO – PLANAR BUT INTERSECTING.
4. WHEN THE SHAFTS ARE AT RIGHT ANGLES AND THE WHEELS ARE
EQUAL IN SIZE THESE ARE CALLED AS “MITRE GEARS”.
5. IF TEETH INCLINED TO THE FACE OF THE BEVEL THESE ARE
CALLED AS “HELICAL BEVEL GEARS”.
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11. APPLICATION OF THE BEVEL GEAR
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12. SPIRAL GEAR
•THESE ARE IDENTICAL TO HELICAL GEARS WITH
POINT CONTACT RATHER THAN LINE CONTACT.
•GEARS USED WHEN CONNECTION IS TO BE MADE
BETWEEN INTERSECTING AND CO-PLANAR SHAFTS.
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13. WORM GEAR
•CONSISTS OF A WORM WHICH IS BASICALLY PART OF
SCREW.
•USED TO CONNECTING TWO NON-PARALLEL,NON
INTERSECTING SHAFTS USUALLY AT RIGHT ANGLES.
•GEAR SYSTEM IS SMOOTH AND QUIET IN OPERATION
AND PROVIDES HIGH GEAR RATIO.
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14. APPLICATION OF WORM GEAR
•ROTATING SPEED OF THE WORM IS QUIET HIGH
COMPARED TO THAT OF WHEEL
•RECOMMENDE WHEN HIGH SPEED REDUCTION IS
REQUIRED(10:1)
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15. RACK AND PINION
RACK IS A STRAIGHT LINE SPUR GEAR OF INFINITE
DIAMETER
IT MESHES BOTH INTERNALLY AND EXTERNALLY WITH
A CIRCULAR WHEEL CALLED PINION
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16. APPLICATION OF RACK AND PINION
RACK IS A STRAIGHT LINE SPUR GEAR OF
INFINITE DIAMETER.
•IT MESHES BOTH INTERNALLY AND
EXTERNALLY WITH A CIRCULAR WHEEL
CALLED PINION.
•ARRANGEMENT FINDS APPLICATION WHERE
LINEAR MOTION IS TO BE CONVERTED IN TO
ROTARY MOTION.
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17. INTERNAL AND EXTERNAL
GEARING
•TWO TOOTHED WHEELS ON PARALLEL SHAFTS MAY
GEAR EITHER EXTERNALLY OR INTERNALLY.
•IN EXTERNAL GEARING ,THE MOTION OF THE TWO
WHEELS IS UNLIKE I.e OPPOSITE DIRECTION.
•THE LARGER WHEEL OF THE GEAR SYSTEM IS KNOWN AS
SPUR AND THE SMALLER WHEEL AS PINION.
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18. INTERNAL GEARING
•THE MOTION OF THE TWO WHEELS IS ALIKE .
BOTH ROTATE IN THE SAME DIRECTION.
•THE EXTERNAL LARGE WHEEL IS CALLED ANNULAR
WHEEL AND THE SMALL INTERNAL WHEEL AS PINION.
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19. GEAR TERMINOLOGY
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
ADDENDUM:
DEDENDUM:
FACE WIDTH:
TOOTH FACE:
TOOTH SPACE:
FACE:
ADDENDUM CIRCLE:
FLANK:
FACE:
PITCH SURFACE ELEMENT:
TOP LAND:
ROOT OR DEDENDUM CIRCLE:
CLEARANCE:
CIEARANCE OR WORKING DEPTH CIRCLE:
TOOL THICKNESS:
TOTAL WIDTH:
CIRCULAR PITCH:
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