ME 114 – Engineering Drawing II

Dr. A. Tolga BozdanaAssistant Professor

Mechanical Engineering

University of Gaziantep

GEAR DRAWING

1

Gear Types

A gear train is combination of two or more gears to change the speed or direction of motion of shaft systems.�

When two gears of different sizes are meshed , the larger is called “gear” while the smaller is “pinion”.�

Gears are used in many applications like automobile engines, household appliances, industrial machine tools.�

A gear is a toothed wheel which is used to transmit power and motion between machine parts.�

Spur Gears

Helical Gears

Spiral Bevel Gears

Straight Bevel Gears

Worm and GearPlanetary Gears

Herringbone Gear

Hypoid Gears Rack & Pinion

2

Gear Tooth Terminology

Total height of the toothWhole Depth:

Distance a tooth projects into mating spaceWorking Depth :

Distance between top of a tooth and bottom of mating space

Clearance :

Thickness of a tooth along the pitch circleTooth Thickness :

Distance on pitch circle from a point on one tooth to corresponding point on the adjacent tooth

Circular Pitch :

Radial distance from pitch to bottom of toothDedendum :

Radial distance from pitch to top of toothAddendum :

Diameter of addendum (outside) circle Outside Diameter :

Diameter of imaginary pitch circle specifying addendum and dedendum

Pitch Diameter :

Diameter of root circleRoot Diameter :

3

Involute Gear Profile

It is unnecessary to follow this procedure to draw gear teeth

since most detail gear drawings employ approximations of gear

teeth. Gear teeth are actually not shown on technical drawings;

instead conventional methods of specifying them are used with

notes and tables.

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Step 2: The chordal distance from point 1 to point 0 is used as

a radius with point 1 as the center. This distance is revolved to

find point 1 on the involute. Then, the distance from point 2 to

the newly found point 1 is revolved to the line tangent to the arc

through point 2 to give point 2 on the involute. This procedure

is followed until the complete involute curve is obtained.

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Step 1: A base arc having the center of base circle is drawn

and divided into equal divisions with radial lines from the center

of arc. Tangents are drawn perpendicular to these radial lines

at the points where they intersect the base arc.

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The method of constructing an involute is illustrated.�

The standard gear profile in an involute that keeps the meshing

gears in contact as the gear teeth are revolved.

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4

Gear Meshing

Line of Action

Gear catalogs are classified according to the number of teeth and

the pressure angle.

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The pressure angle is the angle between the tangent to the pitch

circles and the line of action.

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When two gear teeth are in contact, the kinematic principle of

gearing is demonstrated: the angular velocity ratio of the meshing

gears is constant along the line of action.

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The line of action (also known as “pressure line”) is a line drawn

tangent to the base circle of pinion and gear.

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Meshing of two spur gears with a center distance is shown below.�

5

Detail Drawing of Gears

Spur gears

Bevel gears

Rack and Pinion

Worm and Gear

6

Equations for Cylindrical Spur Gears

z : No. Of Teeth (Diş Sayısı)α : Pressure Angle (Kavrama Açısı) = 15º - 20º (according to DIN 867)

Gear Ratio (Dişli Oranı) :

Center Distance (Merkezler Arası Uzaklık) :

Clearance (Diş Boşluğu) :

Whole Depth (Diş Yüksekliği) :

Dedendum (Diş Dibi Yükseklik) :

Addendum (Diş Üstü Yükseklik) :

Root Dia. (Diş Dibi Çap) :

Pitch Dia. (Bölüm Dairesi Çapı) :

Outside Dia. (Diş Üstü Çap) :

Pitch (Adım) :

Module (Modül) :2

0

+===

z

D

z

Dpm

p

π

2

0

+===

z

D

z

Dmp

p πππ

( )220

+=+= zmmDD p

mDzmDp 2 0

−==

bDhDD pr 220

−=−=

hma

1==

mmb6

7166.1 ==

mmabh6

13166.2 ==+=

mabc 166.0=−=

+=

+=

22

2121zz

mDD

epp

1

2

2

1

z

z

n

n=

7

Gear Bodies

Blank Gear

Pulley Gear

Webbed with

Cores

Stiffener

Spoked

Webbed

There are various types of gear bodies used

in industry. They are preferred according to

their purpose of use (such as light gears by

removing excessive material, strengthened

gear bodies using stiffeners, etc.)

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