One brand of milling machining has the following two index

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One brand of milling machining has the following two index plates supplied along with the indexing head.
Plate 1: 15, 16, 17, 18, 19, 20 hole circles.
Plate 2: 21, 23, 27, 29, 31, 33 hole circles.
It is proposed to mill a spur gear of 28 teeth using simple indexing method. Which one of the following combinations of index plate and number of revolutions is correct?

1. Plate 1: 1 revolution and 9 holes in 18 hole circles
2. Plate 2 :1 revolution and 9 holes in 21 hole circles
3. Plate 2 :1 revolution and 9 holes in 23 hole circles
4. Plate 1 :1 revolution and 9 holes in 15 hole circles

Correct Option: B

		40	=	40	= 1 +	12
		N		28		28

= 1 +		6	= 1 +	9
		14		21

In 1 revolution ,9 hole of 21 hole circle