WHAT IS GEAR | GEAR TERMINOLOGY | MECHANICAL

Gear :

Introduction :

Gear is a simple machine with teeth that increase the force needed to pull or push something. It is transmitt the power.

Gear

एक साधारण मशीन है जो किसी चीज को धक्का देने के लिए आवश्यक बल को बढ़ाती है ..यह पावर को ट्रांसमिट करती है!

Gear terminology :-

1.pitch circle :-

it is an imaginary circle which by pure rolling action would give the same motion as the actual gear.

2. Pitch circle diameter:-

It is the diameter of the pitch circle. the size of the gear is usually specified by the pitch circle diameter .it is also called pitch diameter.

3. Pitch point :-

It is the common point of contact between two gears.

4 Addendum:-

It is a radial distance of a tooth from the Pitch Circle to the top of the tooth.

5.Dedendum:-

it is a radial distance of a tooth from pitch circle to the bottom of the tooth.

6. Addendum circle:-

It is the circle drawn through the top of the teeth and is concentric with the pitch circle.

7. Dedendum circle:-

It is the circle drawn through the bottom of the teeth and is also called root circle.

8. circular pitch:-

It is the distance measured by the circumference of the pitch from a point of one tooth to the corresponding point at next tooth .

9. diametral pitch :-

It is the ratio of number of teeth to the pitch circle diameter.

diametral pitch =T/D

10. Module :-It is the ratio of Pitch Circle diameter to number of teeth it is denoted by m.

m = D/T

11. clearance :-

It is the radial distance from the top of the tooth to the bottom of the tooth in meshing gear. A circle passing through the top of the meshing gear is known as clearance circle.

12. Total depth :- It is the radial distance between addendum and dedendum of a gear. it is equal to the sum of addendum and dedendum.

13 .Working depth.:- It is the radial distance from the addendum circle to the clearance circle.

It is equal to the sum of the addendum of the two meshing gears.

14. Tooth thickness. It is the width of the tooth measured along the pitch circle.

15.Tooth space . It is the width of space between the two adjacent teeth measured along the pitch

circle.

16. Backlash. It is the difference between the tooth space and the tooth thickness, as mea-

sured along the pitch circle. Theoretically, the backlash should be zero, but in actual practice some

backlash must be allowed to prevent jamming of the teeth due to tooth errors and thermal expansion.

17.Face surface :-It is the surface of the gear tooth above the pitch surface.

18.Flank of tooth.:- It is the surface of the gear tooth below the pitch surface.

19.Top land. :-It is the surface of the top of the tooth.

20.Profile. It is the curve formed by the face and flank of the tooth.

.21.Fillet radius. It is the radius that connects the root circle to the profile of the tooth.

.22. Path of contact :- It is the path traced by the point of contact of two teeth from the

beginning to the end of engagement

23.Arc of contact. It is the path traced by a point on the pitch circle from the beginning

to the end of engagement of a given pair of teeth. The arc of contact consists of two parts, i.e.

(a) Arc of approach. It is the portion of the path of contact from the beginning of the

engagement to the pitch point.

(b) Arc of recess. It is the portion of the path of contact from the pitch point to the end of the

engagement of a pair of teeth.

Note : The ratio of the length of arc of contact to the circular pitch is known as contact ratio i.e. number of pairs

of teeth in contact.

Let ;

L = end of engagement,

K = start of engagement

It is the equation of lenght of path of contact in a meshing gear..