Question

Which of the following is not true for the periodic error in worm and gear rotary table?

(a) It can be affected by tooth spacing of the gear

(b) This error is not taken into consideration

(c) It can be affected by the thread form

(d) It is the error within two turn of the hand wheel

The question was posed to me in an online interview.

This intriguing question originated from Rotary Tables in chapter Angular Measurement and Circular Division of Engineering Metrology

Answer 1

Correct choice is (d) It is the error within two turn of the hand wheel

For explanation I would say: The periodic error is the error within one turn of the hand wheel. It is not taken into consideration. This error is affected by factors like the thread form and tooth form, drunkenness, line up, runout of worm, errors of eccentricity, and spacing of tooth of the gear.