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GEAR TERMINOLOGY
CONTENTS
TERMINOLOGY
MANUFACTURING
ERRORS
GEAR AND PINION
Gears are the most common means of transmitting power in mechanical engineering.
Gear or wheel. The larger of two interacting gears.
Pinion. The smaller gear in a pair.
BASE CIR CIRCLE CLE
Base
circle : It is a circle from which involute form is generated. Only the base circle on a gear is fixed fixed and unalterable.
Base
pitch ( p pb): It is the distance from one face of a tooth to the corresponding corresponding face of an adjacent tooth on the same gear, measured along the base circle. Sometimes called the 'normal pitch'.
PITCH CIRCLE
Pitch is the distance between a point on one tooth and the corresponding point on an adjacent tooth.
Pitch circle. A circle, centered on and perpendicular to the axis, and passing through the pitch point. Sometimes also called the 'pitch line', although it is a circle.
Pitch diameter (D). Diameter of a pitch circle. The nominal gear size
Circular
pitch (p). The distance from one face of a tooth to the corresponding face of an adjacent tooth on the same gear, measured along the pitch circle.
Diametral
pitch (Pd). The ratio of the number of teeth to the pitch diameter.
Module(m).
The module of a gear is equal to the pitch diameter divided by the number of teeth.
ADDENDUM AND DEDENDUM
Addendum : The radial distance from the pitch surface to the outermost point of the tooth.
Dedendum : The radial distance from the depth of the tooth to the pitch surface.
POINT OF CONTACT A is a n y p o in t a t w h ich tw o to o th p ro file s to to u ch e a ch o th e r. The is the point of tange ngency of two pitch circles and is on the line of centers.
LINE OF ACTION
The line of action is also called path of action.
It is the straight line passing through the pitch point and tangent to both base circles.
LANDS
Bottom land is the surface at the bottom of a gear tooth space adjoining the fillet.
Top land is the (sometimes flat) surface of the top of a gear tooth.
ANGLES ASSOCIATED WITH GEARS
Helix angle (ψ). The angle between a tangent to the helix and the gear axis. It is zero in case of a spur gear.
Lead angle (λ). The angle between a tangent to the helix and a plane perpendicular perpendicular to the axis. It is the complement of the helix angle which is usually given for helical gears.
Pressure angle (ø). The complement of the angle between the direction, that the teeth exert force on each other, and the line joining the centers of the two gears. The pressure angle is a constant for a given gear.
MANUFACTURING OF GEARS
The gears (gear teeth) are generally made by one of the following 2 methods.
1. Reproducing
method, in which the cutting tool is a formed involve cutter, which forms the gear teeth profiles by reproducing the shape of the cutter itself. itself. In this method, each tooth space is cut independently of the other tooth spaces.
2. 3. Generating
method, in which the cutting tool (hob) forms the profiles of several teeth simultaneously during constant relative relative motion of the tool and blank.
SOURCES OF ERRORS
The various sources of errors in the gear made by reproducing method be due to
incorrect 1. incorrect
profile on the cutting tool,
2.
incorrect 3. incorrect
positioning of the tool in relation to the work and,
4.
incorrect 5. incorrect
indexing of the blank.
SOURCES OF ERRORS
The sources of error in the gear made by generating method are:
1. Errors Errors
in the manufacture of the cutting tool
2.
Errors 3. Errors
in positioning the tool in relation to the work and
4.
Errors 5. Errors
in the relative motion of the tool too l and blank during the generating operation.
GEAR ERRORS Pitch
error It is the difference between actual and design pitch.
Cyclic
error
Error occurs in each revolution of gear.
Undulation
It is the periodical departure of the actual tooth surface from the design surface.
GEAR ERRORS Run
out Total range of a fixed indicator with the contact points applied to a surface rotated, without axial movement, about a fixed axis.
Periodic
error Error Error occurs at regular intervals.
Profile
error The maximum distance of any point on the tooth profile form to the design profile.
GEAR ERRORS
Radial run out Run out is measured along a perpendicular to the axis of rotation.
Axial run out Run out is measured parallel to the axis of rotation.
Eccentricity It is the half radial run out.
BACKLASH Backlash
is the error in motion that occurs when gears change direction. direction.
It
exists because there is always some gap between the trailing face of the driving tooth and the leading face of the tooth on the driven gear, and that gap must be closed before force can be transferred in the new direction. direction.