Gear Tooth Geometry - This is determined primarily by pitch, depth and pressure angle

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Gear Tooth Geometry - This is determined primarily by pitch, depth and pressure angle Addendum: The radial distance between the top land and the pitch circle.

1 Gear Tooth Geometry - This is determined primarily by pitch, depth and pressure angle Addendum: The radial distance between the top land and the pitch circle. Addendum Circle: The circle defining the outer diameter of the gear. Circular Pitch: The distance along the pitch circle between the corresponding points of 2 adjacent teeth. Equals to the sum of the tooth thickness and space width. Clearance: The radial distance between the bottom land and clearance circle. Dedendum Circle: The circle through the bottom lands of a gear. Dedendum: The radial distance between the pitch circle and the dedendum circle. Depth: A number which is standardized in terms of pitch. Full depth teeth have a working depth of 2/DP. For gears with equal addenda, then the addendum is 1/P. Diametral Pitch (DP): The ratio of the teeth to the pitch diameter. It is used in the U.S. to indicate the coarseness of a gear and an index of tooth size expressed in teeth per inch. Pitch: A standard pitch is typically a whole number when measured as a diametral pitch (DP). Coarse-pitch gears have DP less than 20. Fine-pitch gears have DP larger than 20. Involute-tooth gears can be made with DP as fine as 200, and cycloidal tooth gears can be made with DP to 350. Pitch Circle: Theoretical circle upon which all calculations are made. This is the circle that rools without slipping with the pitch circle of the mating gear. Pitch Diameter: The diameter of the pitch circle in inches or metric (mm). Pressure Angle: The angle between the tooth profile and a perpendicular to the pitch circle, usually at the point where the pitch circle meets the tooth profile. Standard angles are 20 and 25 degrees. The pressure angle affects the force that tends to separate mating gears. A high pressure angle means that higher ratio of teeth not in contact. However, this allows the teeth to have higher capacity and also allows fewer teeth without undercutting.

Power Velocity Load Power is transmitted by one gear exerting a force on the other gear as follows: F=33000 hp/v where F= force on the gear tooth (lb) hp= horsepower transmitted V= velocity at pitch

2 Power Velocity Load Power is transmitted by one gear exerting a force on the other gear as follows: F=33000 hp/v where F= force on the gear tooth (lb) hp= horsepower transmitted V= velocity at pitch circle (ft/min) = 0.262*Pitch Diameter(ft)*Rotational Speed(rpm) Gear Strength The maximum allowable load on a gear is calculated as follows: F s = s*f*y/p where F s = allowable load (lb) s= allowable stress, psi f= face width or width of the gear tooth Y= tooth form factor which can be obtained from engineering handbooks P= Diametral pitch The allowable load should be multiplied by a factor K to allow for shock loads and manufacturing imperfections. The factor K for accurately hobbed gears rotating at less than 4000 ft/min is calculated as follows: K = 1200/(1200+V) Backlash The backlash clearance for most gear applications is approximately 0.04/P. The backlash or force tending to separate two meshing gears carrying a load is: S=F*tan α where: S= separating force (lb) α= tooth pressure angle Gear Classification Spur Gears: cylindrical gears with teeth that are straight and parallel to the axis of rotation.

Spur Gears are the most common type of gear in use. The spur gear is manufactured on a cylindrical blank and is used in applications where input and output are in parallel planes, i.e. they are used to transmit motion between parallel shafts.

Spur gears are used to drive externally where the pinion and gear mating surfaces are located on the outside diameter or they drive internally where the outside diameter of one member drives the

3 Spur Gears are the most common type of gear in use. The spur gear is manufactured on a cylindrical blank and is used in applications where input and output are in parallel planes, i.e. they are used to transmit motion between parallel shafts. The teeth generally have full-face contact though length-wise crowning is possible. Spur gears are used to drive externally where the pinion and gear mating surfaces are located on the outside diameter or they drive internally where the outside diameter of one member drives the inside diameter of the other member such as in a planetary system. Spur gears tend to be noisy at higher speeds. Helical Gears: cylindrical shape also but their teeth are set at an angle to the axis. The helix angle on a helical gear was introduced to achieve higher performance out of parallel axis gear sets. The helical tooth form brings more teeth into mesh than a spur gear is capable of. This load sharing increases the overall power capability of the gear set and also allows for quieter, smoother operation at high speeds. - Unwin's Construction Unwin's Construction is a way to draw an approximation to an involute gear profile. It is suitable for either hand-drawn technical drawings or for CAD drawings. Before you start Unwin's Construction, you need the following dimensions: Addendum, a Dedendum, b Pitch Diameter, D Tooth Thickness Fillet Radius at base of tooth 1. Draw the pitch circle, diameter D, about the the centre of the gear, O. This is shown in red. 2. Draw the outside diameter (green) by drawing a circle about O with a radius greater than the pitch circle by the value of the addendum. 3. Draw the root diameter (light blue) by drawing a circle about O with a radius smaller than the pitch circle by the value of the dedendum.

Draw a circle about O which is tangent to the line of action. This is the base circle and is shown in dark blue. 1. Mark point A on the outside circle (green). 2.

4 1. Draw a tangent to the pitch circle (pink). 2. Draw a line (orange) through the intersection of the tangent with the pitch circle which makes an angle equal to the pressure angle, φ, with the tangent. This line is the line of action 3. Draw a circle about O which is tangent to the line of action. This is the base circle and is shown in dark blue. 1. Mark point A on the outside circle (green). 2. On the line colinear with A and O, mark point B on the base circle (dark blue). 3. Divide the distance AB into 3 equal parts. Mark point C on the line between A and B such that AC is one third of AB. 1. Draw a line from C tangent with the base circle. 2. Mark the point of tangency, D. 3. Divide the distance DC in to 4 equal parts, and mark in point E such that DE is one quarter of DC.

5 1. Draw in a circle about point E, passing through point C. This is part of the flank of the gear tooth and is shown in orange. 2. Ignore the rest, easier way in solid works About the point C draw a circle with the radius of the tooth thickness. Where it cuts the pitch circle, mark point F. This point is on the flank of the other side of the tooth. 1. Draw in the fillet between the flank and the base circle. 2. Draw the profile radius, EC, from F. This arc is shown in dark green. 1. Draw the profile radius, EC, from G. This is the other flank of the tooth. 2. Add the fillet at the base of the tooth as before.

6 -commons.wikimedia.org/wiki/unwin's_construction 1. The tooth is now complete. The outside circle between the two flanks is the top of the tooth. 2. This can be repeated for each tooth.

Lecture (7) on. Gear Measurement. By Dr. Emad M. Saad. Industrial Engineering Dept. Faculty of Engineering. Fayoum University.

Lecture (7) on. Gear Measurement. By Dr. Emad M. Saad. Industrial Engineering Dept. Faculty of Engineering. Fayoum University. 1 Lecture (7) on Gear Measurement Fayoum University By Dr. Emad M. Saad Industrial Engineering Dept. Faculty of Engineering Fayoum University Faculty of Engineering Industrial Engineering Dept. 2015-2016