12) What is the angle of counter sink rivet head?

13) What is the angle of beveled heads of counter sink head screws?

14) Which type fo drilling machine is best suited to drill multiple holes in a work piece in a single setting?

15) Calculate the cutting speed used for drilling a 20 mm dia meter hole in a mild steel work piece with a rpm of 399?

16) Calculate the rpm for drilling a hole of dia meter 16 mm on cast iron with a cutting speed 30 m / minute?