# Engineering Metrology Questions and Answers – Terminology of Gear Tooth

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This set of Engineering Metrology Multiple Choice Questions & Answers (MCQs) focuses on “Terminology of Gear Tooth”.

1. Which of the following is the correct mathematical formula for module?
a) D/N
b) D/2N
c) 2D/N
d) 4D/N

Explanation: Module is defined as the length of the pitch circle diameter / tooth. Thus, if Pitch Circle Diameter of gear is D and number of teeth is N, then module (m) is equal to D/N. It is generally expressed in millimeter.

2. What is the standard value of clearance? (Where, m is module)
a) 0.572 x m
b) 0.182 x m
c) 0.157 x m
d) 0.821 x m

Explanation: Term clearance used in terminology of gear tooth is the radial distance from the tooth top to the bottom of a mating tooth space when the teeth are engaged symmetrically. Standard value of clearance is 0.157 m where m is module.

3. What is the value of addendum?
a) 1 module
b) 2 modules
c) 3 modules
d) 4 modules

Explanation: This is the radial distance from the pitch circle to the tooth tip. Its value is equal to 1 module. Another term diametral pitch is defined as a number of teeth per inch of pitch circle diameter.

4. What is dedendum?
a) Addendum + 2 x clearance
b) Addendum + clearance / 2
c) 2 x Addendum + clearance

Explanation: Dedendum is the radial distance from the pitch circle to the bottom of the tooth space. Dedendum is equal to Addendum plus Clearance = m + 0.157 m = 1.153 m as one addendum is a module and standard value of clearance is 0.157 m.

5. What is the flank of tooth?
a) Part of the surface of tooth which is above the pitch surface
b) Part of the surface of tooth which is below the pitch surface
c) Part of the surface of tooth which is in the middle of top and bottom of the pitch surface
d) Part of the surface of tooth which is at the top of the pitch surface

Explanation: Face of the tooth is that part of the tooth surface which is lying above the pitch surface. Flank of Tooth is that part of the tooth surface which is below the pitch surface.
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6. What is tooth thickness?
a) Circular pitch / 2
b) Circular pitch / 4
c) 2x Circular pitch
d) 4 x Circular pitch

Explanation: Thickness of tooth is the distance of arc measured along the pitch circle from its intercept with one flank to its intercept with the other flank of the same tooth.
Tooth thickness = C.P./2 or πm/2.

7. What is the name of angle which is present between line of action and common tangent to the pitch circles?
a) Helix angle
c) Pitch angle
d) Pressure angle

Explanation: The angle between the line of action and the common tangent to the pitch circles is called as pressure angle. The standard values of pressure angle are 14.5 degree and 20 degree. Pressure angle is generally represented by φ.

8. Which of the following is not the correct formula for base pitch?
a) Base circumference / Number of teeth
b) π x Base circle diameter / N
c) π x D sinφ / N
d) π x m x cosφ

Explanation: Base pitch is the distance which is measured around the base circle from the origin of the involute on the tooth to the origin of a involute (similar) on the next tooth.
Base pitch = Base circumference / Number of teeth
= π x Base circle diameter / N = π x D cosφ / N = π x m x cosφ.

9. What is blank diameter?
a) Pitch circle diameter plus addenda
b) Pitch circle diameter plus twice the addenda
c) Base circle diameter plus addenda
d) Base circle diameter plus twice the addenda

Explanation: Blank diameter is that diameter of blank from which gear is out. Blank diameter is equal to the pitch circle diameter plus addenda.
Blank diameter = mN + 2m = m x (N + 2).

10. Which of the following is not necessary to find normal module of helical gear?
a) Number of teeth
b) Pitch diameter
c) Helix angle
d) Tooth thickness

Explanation: The formula for normal module of helical gear is mn = (D/N) cosα where N is number of teeth, D is pitch diameter and α is helix angle. Also, mn = pn /π where pn is normal circular pitch.

11. What is worm lead in worm and worm gear?
a) Nw x 2px
b) Nw x 4px
c) Nw x px
d) Nw / px

Explanation: Worm lead is represented by L and L = Nw x px where, Nw is number of threads in worm and is px axial pitch. Lead angle in worm and worm gear is represented by ψ and tanψ = L/πd where d is pitch diameter.

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