The time taken to drill a hole of diameter 25 mm in a 30 mm thick steel plate with a feed of 1 mm/rev and the drill spindle speed being 60 rpm is _________ seconds.

Concept:

Drilling time can be calculated by;

\(T = \frac{L}{{f ~×~ N}}\)

where T = Machining time in min, L = (Approach Length + Thickness of plate) in mm, f = Feed (mm/rev), N = Speed in rpm (revolution per min)

\(Approach\ Length= \frac{D}{2\ tanθ}\)

Where θ = Half drill bit angle, D = diameter of the hole

∵ The angle of a drill bit is not given in the question hence we will take approach length zero.

∴ L = Thickness of the plate

Calculation:

Given:

Thickness of plate (L) = 30 mm, Feed (f) = 1 mm/rev, Speed (N) = 60 rpm, Hole diameter (d) = 25 mm

\(T = \frac{30}{{1 × 60}}\)

T = 0.5 min

T = 0.5 × 60 sec

T = 30 sec

Hence drilling time will be 30 sec.

Important Points

If in the ques it is given that "Neglect approach and over travel" OR "Drill bit angle is not given" then effective length equal thickness of the workpiece.