This set of Engineering Metrology Multiple Choice Questions & Answers (MCQs) focuses on “Effect of Pitch Errors”.

1. What is the effect of pitch error?

a) Increase effective diameter of bolt

b) Decrease effective diameter of screw

c) Increase effective diameter of nut

d) Increase effective diameter of both nut and screw

View Answer

Explanation: An error in pitch increases the effective diameter of a screw or bolts virtually and virtually decreases the effective diameter of a nut. The meaning of the virtual change is that if any screw is perfect except for pitch error, if its effective diameter is not reduced, it will not easily screwed into a perfect ring gauge of same nominal size.

2. What is the virtual change in effective diameter caused by pitch error in whitworth thread?

a) 1.821 X pitch error

b) 1.921 X pitch error

c) 1.111 X pitch error

d) 1.211 X pitch error

View Answer

Explanation: If p is the error in a pitch for a whitworth thread, then the virtual increase or decrease in the thread effective diameter in case of bolt or nut is given by the formula: Virtual change in effective diameter = 1.921 x p.

3. What is the virtual change of effective diameter of bolt or nut in case of whitworth thread in terms of error in flank angle?

a) 0.1921 X p(θ_{1} + θ_{2})

b) 0.182 X p(θ_{1} + θ_{2})

c) 0.0195 X p(θ_{1} + θ_{2})

d) 0.0105 X p(θ_{1} + θ_{2})

View Answer

Explanation: A Corresponding reduction in the effective diameter is also needed for the errors in flank angles, if the screw or nut is to fit a perfect ring gauge of the same nominal size. Formula for virtual change in effective diameter is : 0.0105 X p(θ

_{1}+ θ

_{2}). Where p is the normal pitch and θ

_{1}and θ

_{2}are the error in flank angles.

4. Which of the following is periodic pitch error?

a) Successive portion of thread is longer than the mean

b) Successive portion of thread is shorter than the mean

c) Successive portion of thread is longer or shorter than the mean

d) Successive portion of thread is neither longer nor shorter than the mean

View Answer

Explanation: Periodic pitch error repeats itself along the thread at regular intervals of time. In this type of error, successive thread portions are either shorter or longer than the mean. It occurs when the tool velocity work ratio s not constant.

5. What is the formula of virtual effective diameter in case of unified threads?

a) Simple effective diameter + [ (1.73 x pitch error) + 0.0098 p (θ_{1} + θ_{2})].

b) Simple effective diameter – [ (1.73 x pitch error) + 0.0098 p (θ_{1} + θ_{2})].

c) Simple effective diameter + [ (1.59 x pitch error) + 0.0098 p (θ_{1} + θ_{2})].

d) Simple effective diameter – [ (1.59 x pitch error) + 0.0098 p (θ_{1} + θ_{2})].

View Answer

Explanation: For unified thread total virtual effective diameter is Simple effective diameter + [ (1.73 x pitch error) + 0.0098 p (θ

_{1}+ θ

_{2})] while in case of metric thread it is Simple effective diameter + [ (1.722 x pitch error) + 0.0131 p (θ

_{1}+ θ

_{2})].

6. Which of the following is not correct when minor and major diameter have errors?

a) Will cause interference between mating parts

b) Flank contact increases

c) Less root section

d) Less wall thickness

View Answer

Explanation: Errors on the minor and major diameters will cause interference in the mating thread. Due to errors in minor and major diameter, the wall thickness and root section will be less, also the flank contact will be decreases and the component will be weak in strength.

7. Which of the following are main elements, error in any of these can cause rejection of thread?

a) Major diameter and minor diameter

b) Major diameter, minor diameter and effective diameter

c) Major diameter, minor diameter, effective diameter and pitch

d) Major diameter, minor diameter, effective diameter, angle of thread and pitch

View Answer

Explanation: In case of plain holes and shafts, there is one dimension only which has to be considered i.e. diameter. Errors in diameter if exceed the permissible tolerance, will result in rejection of part. But in case of screw threads there are minimum 5 important elements which are Major diameter, minor diameter, effective diameter, angle of thread and pitch and error in any one of these will result rejection of the thread.

8. What is the nature of the graph between cumulative pitch error and length of thread in case of progressive pitch error?

a) Straight line

b) Parabolic

c) Hyperbolic

d) Exponential

View Answer

Explanation: Progressive pitch error can be caused due to pitch error in any generating machine or in the lead screw of a lathe. The graph between cumulative pitch error and thread length in progressive pitch error is a straight line.

9. Which of the following is the correct option for given statements about the effect of pitch error?

Statement 1: Pitch error can cause progressive tightening on assembly.

Statement 2: Tool work velocity ratio will play an important role to prevent pitch errors.

a) T, F

b) F, F

c) F, T

d) T, T

View Answer

Explanation: The threads are commonly generated by a point cutting tool. For pitch to be correct, the ratio of the tool linear velocity and work’s angular velocity must be correct and constant, otherwise pitch errors will occur.

10. Which of the following is not related to the drunken thread?

a) Periodic pitch error

b) Erratic pitch error

c) Progressive pitch error

d) Irregular pitch error

View Answer

Explanation: Drunken thread has erratic pitch, in which the advance of the helix is irregular in thread’s 1 complete revolution. Thread drunkenness is a case of a periodic pitch error recurring at regular intervals of 1 pitch.

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