Spur Gears
A type of gears in which teeth are cut parallel to the axis of the shaft is known as spur gears.
As the teeth are parallel to the axis of the shaft, spur gears are used only when the shafts are parallel.
-:Terminology of Spur Gears:-
The terminology applied to spur gears is illustrated in figure-
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| Image source: Google |
1- Pitch circle:- An imaginary circle that rolls without slipping with the pitch circle of a mating gear is known as pitch circle.
OR
An imaginary circle by which pure rolling action, would give the same motion as the actual gear is known as pitch circle.
2- Pitch circle diameter:- The diameter of the pitch circle is known as the pitch circle diameter. It is also called pitch diameter.
3- Pitch point:- A common point of contact between two pitch circles is known as pitch point.
4- Pitch surface:- The pitch surface of the gears are imaginary planes, cylinders or cones that roll together without slipping.
5- Pressure angle/ Angle of obliquity:- The angle between the common normal to two gear teeth at the point of contact and the common tangent at the pitch point is known as pressure angle or angle of obliquity.
6- Addendum:- The radial distance of a tooth from the pitch circle to the top of the tooth is known as addendum.
7- Addendum circle:- An imaginary circle that borders the tops of gear teeth in the cross section is known as addendum circle .
8- Dedendum :- The radial distance of a tooth from the pitch circle to the bottom of the tooth is known as Dedendum .
9- Dedendum circle:- An imaginary circle which drawn through the bottom of the teeth is known as Dedendum circle. It is also known as root circle.
10- Clearance:- The radial distance from the top of the tooth to the bottom of the tooth, in a meshing gear is known as Clearance.
A circle passing through the top of the meshing gear is known as clearance circle.
11- Total depth:- The radial distance between the addendum and Dedendum circle of a gear is known as total depth . It is equal to the sum of the addendum and Dedendum.
12- Working depth:- The radial distance from the addendum circle to the clearance circle is known as working depth. It is equal to the sum of the addendum of the two meshing gears.
13- Tooth thickness :- The width of the tooth measured along the pitch circle is known as tooth thickness.
14- Tooth space:- The width of space between the two adjacent teeth measured along the pitch circle is known as tooth space.
15- Backlash:- The difference between the tooth space and the tooth thickness , as measured on the pitch circle is known as backlash.
16- Face of the tooth:- The surface of the tooth above the pitch surface is known as face of the tooth.
17- Top land :- The surface of the top of the tooth is known as top land .
18- Flank of the tooth:- The surface of the tooth below the pitch surface is known as flank of the tooth.
19- Face width:- The width of the gear tooth measured parallel to its axis is known as face width.
20- Profile:- The curve formed by the face and flank of the tooth is known as profile .
21- Fillet radius:- The radius that connects the root circle to the profile of the tooth is known as fillet radius.
22- Path of contact:- The path traced by the point of contact of two teeth from the beginning to the end of engagement.
23- Contact ratio:- 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.
14- Tooth space:- The width of space between the two adjacent teeth measured along the pitch circle is known as tooth space.
15- Backlash:- The difference between the tooth space and the tooth thickness , as measured on the pitch circle is known as backlash.
16- Face of the tooth:- The surface of the tooth above the pitch surface is known as face of the tooth.
17- Top land :- The surface of the top of the tooth is known as top land .
18- Flank of the tooth:- The surface of the tooth below the pitch surface is known as flank of the tooth.
19- Face width:- The width of the gear tooth measured parallel to its axis is known as face width.
20- Profile:- The curve formed by the face and flank of the tooth is known as profile .
21- Fillet radius:- The radius that connects the root circle to the profile of the tooth is known as fillet radius.
22- Path of contact:- The path traced by the point of contact of two teeth from the beginning to the end of engagement.
23- Contact ratio:- 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.
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