Question

Base diameter of a conical helix is 60 mm, height of spring is 30 mm, angle between the base and slanting side of cone is 45 degrees and diameter of wire is 3 mm. What is the outer diameter at the top edge of spring?

(a) 14

(b) 15

(c) 30

(d) 18

The question was posed to me in an international level competition.

My question is taken from Helix upon a Cone in portion Curves used in Engineering Practice of Engineering Drawing

Answer 1

Right choice is (b) 15

The best explanation: Since the given angle is 45 degrees the max height of helix is equal to radius of base. Height given is 30 mm due to wire diameter the total helix height will be 26. 30 -26 =4 will be the radius of top end helix and due to diameter of wire the outer diameter of top end is 4 x 2 + 3= 15 mm.