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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