# Drilling Time Calculation for gate,ese, ssc jee preparation

In this blog, we will learn how to calculate the time required to drill the hole so there are two cases of drill calculation lets discuss it

Case 1. when drill bit angle is zero

we know time(T) = distance/speed   T = L/fN               ....(1)

here the L (total distance travel by the tool) = t1 + Ad + Od + Cd (for zero drill bit Cd is zero)

t1 = thickness of the job

Ad = Approach distance (distance between the drill and the job before drilling)

Od = Over distance (distance between the drill and job AFTER drilling)

Cd = compulsory distance(it is zero here we will talk about in case 2)

f = feed rate

N = rpm of drill (when we use in formula we convert it into rps [rotation per second])

Let's try to understand with the gate numerical

### The time taken to drill a hole through a 25mm thick plate with their drill rotating at 300 rpm and moving at a feed rate of 0.25mm/rev is  [ME 2002]

a. 10-sec b. 20-sec c. 60sec    d. 100 sec

Given:  thickness is 25mm

N = 300rpm = 5rps (rpm = revolution per minute , rps = revolution per second)

here Ad, Od is zero because they are not given

and Cd is zero for zero degrees drill bit

here feed rate .25mm/rev when a drill rotate a revolution it will move downward .25mm

let apply the formula from equation 1 (All units here in mm and  time in seconds)

T = 25 +0+0+0/ (0.25 X 5) =  20 sec

In a single pass drilling operation, a through hole of 15 mm diameter is to
be drilled in a steel plate of
50 mm thickness. Drill spindle speed is 500 , rpm
feed is 0.2  mm /rev and drill point angle is 118c. Assuming 2 mm clearance
at approach and exit, the total drill time (in seconds) is

Given : d = 15mm t =50mm f =0.2mm/rev  theta = 118

clearance at approach = 2 mm

clearance at exit= 2 mm