# Engineering Metrology Questions and Answers – Sources of Errors in Manufacturing Gears

This set of Engineering Metrology Question Bank focuses on “Sources of Errors in Manufacturing Gears”.

1. Which of the following is true for generating method of gear formation?
a) No use of cutter
b) Profiles of several teeth are formed simultaneously
c) Linear motion of the tool and the blank is not constant
d) Each tool space is cut independently

Explanation: Gear teeth are generally made by two methods, reproducing method and generating method. Method in which the cutting tool forms the several teeth profiles simultaneously during constant relative motion of the blank and tool is known as Generating method.

2. Which of the following is true for high power gears?
a) Operated at low speed
b) Operated at high speed
c) Operated at moderate speed
d) Operated at high or moderate speed

Explanation: High power gears are operated at low speeds generally but it has to transmit large force. Therefore for this purpose the gear teeth should specify fullest possible contact along the tooth length.

3. Which of the following gear is used for counting and timing purposes?
a) High speed gears
b) High power gears
c) Low speed gears
d) Precision gears

Explanation: Constant gearing ratio is the main requirement of the precision gears. Precision gears are generally used for indexing devices and measuring instruments, or in counting and timing purposes, and usually have small face width and small module.

4. What is the kinematic error in gears?
a) Minimum error in gear rotation per gear revolution
b) Accumulated permissible error in gear rotation per gear revolution
c) Maximum error in gear rotation per gear revolution
d) Accumulated permissible error in gear rotation in two gear revolutions

Explanation: Kinematic error is defined as the permissible accumulated error in gear rotation per gear revolution. The kinematic accuracy index is the maximum kinematic error. It can be defined as the maximum angular error in gear rotation, when it meshes in single-profile engagement with a precise gear.

5. What is profile error?
a) The minimum distance of any point on the profile of tooth form and normal to the design profile when the two coincide at the reference circle
b) The minimum distance of any point on the profile of tooth form and parallel to the design profile when the two coincide at the reference circle
c) The maximum distance of any point on the profile of tooth form and parallel to the design profile when the two coincide at the reference circle
d) The maximum distance of any point on the profile of tooth form and normal to the design profile when the two coincide at the reference circle

Explanation: Profile error is a possible error on spur, helical or bevel gear etc. It is the max distance of any point on the profile of tooth and normal to the design profile when two coincide at the reference circle.
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6. What is a cyclic error?
a) Mean value of the discrete values of variation in the kinematic error of the gear taken for all cycles during one revolution
b) Mean value of the range of variation in the kinematic error of the gear taken for all cycles during one revolution
c) Mean value of the range of variation in permissible deviations in basic pitch of the gear taken for all cycles during one revolution
d) Mean value of the range of variation in the angular error of the gear taken for all cycles during one revolution

Explanation: The cyclic error is defined as the mean value of the range of variation in the kinematic error of the gear which is taken for all cycles during 1 revolution. It can also be explained as an error which occurs during each revolution of the element under consideration.

7. How bearing contact of mating gears is represented?
a) By the relative size of the bearing contact pattern in mm
b) By the relative size of the bearing contact pattern in cm
c) By the relative size of the bearing contact pattern in meter
d) By the relative size of the bearing contact pattern in percent

Explanation: Bearing contact for mating gears is represented by the relative size of the bearing contact pattern in % and along the length of tool it is represented by the ratio of the traces of contact, subtracting gaps larger than the size of the module, to the full tooth length.

8. Another name for Wobble ______________
b) Eccentricity
c) Composite error
d) Axial run-out

Explanation: Run out is the total range of reading of an indicator with the contact point applied to a rotated surface, without axial movement about an axis which is fixed. Axial runout is the runout measured parallel to the rotation axis, at a specified distance.

9. What is undulation?
a) Departure of the actual tooth surface from design surface
b) Departure of the virtual tooth surface from design surface
c) Departure of the design surface from actual tooth surface
d) Departure of the design surface from virtual tooth surface

Explanation: Undulation is a departure of the actual tooth surface from the design surface and undulation height is the normal distance between 2 surfaces that contain the crests and the troughs of the tooth undulation.

10. Which of the following is true for eccentricity?
b) Half the axial run-out
c) Equal to the radial run-out
d) Equal to the axial run-out

Explanation: Radial runout is the runout measured along a perpendicular to the rotation axis. Eccentricity is half the radial run-out.

11. Which of the following can be used to ensure smoothness of gear operation?
a) By limiting the minimum permissible deviation in base circle
b) By limiting the maximum permissible deviation in base circle
c) By limiting the maximum permissible deviation in basic pitch
d) By limiting the minimum permissible deviation in basic pitch

Explanation: Smoothness of gear operation is important to provide for noiseless engagement and longer service life of gearing. The smoothness of gear operation can be ensured by limiting the maximum permissible deviations in basic pitch.

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