Question

A through hole of 10 mm diameter is to be drilled in a mild steel plate of 30 mm thickness. The selected spindle speed and feed for drilling hole are 600 revolutions per minute (RPM) and 0.3 mm/rev, respectively. Take initial approach and breakthrough distances as 3 mm each. The total time (in minute) for drilling one hole is ______. (Rounded off to two decimal places) 
 

Hint:

In drilling time calculations, never forget to include the approach and breakthrough distances to the plate thickness to find the total length the drill must travel. The time is simply total distance divided by speed (feed rate).

Answer 1

Step 1: Understanding the Question:
The problem asks to calculate the total time required to drill a through hole in a steel plate. We are given all the necessary parameters: plate thickness, drill speed, feed rate, and additional distances for approach and breakthrough.
Step 2: Key Formula or Approach:
The total time for drilling (\(T_m\)) is calculated by dividing the total length the drill has to travel (\(L\)) by the feed rate of the drill (\(f_m\)). \[ T_m = \frac{L}{f_m} \] Where:

• Total drilling length, \(L = \text{Plate Thickness} + \text{Approach Distance} + \text{Breakthrough Distance}\)
• Feed rate, \(f_m = \text{Feed per revolution} (f) \times \text{Spindle Speed} (N)\)

Step 3: Detailed Explanation:
1. Identify the given data:

• Plate Thickness, \(t = 30\) mm
• Spindle Speed, \(N = 600\) RPM (revolutions per minute)
• Feed, \(f = 0.3\) mm/rev
• Approach Distance, \(A = 3\) mm
• Breakthrough Distance, \(B = 3\) mm

2. Calculate the total drilling length (L): \[ L = t + A + B \] \[ L = 30 \, \text{mm} + 3 \, \text{mm} + 3 \, \text{mm} = 36 \, \text{mm} \] 3. Calculate the feed rate (\(f_m\)) in mm per minute: \[ f_m = f \times N \] \[ f_m = 0.3 \, \frac{\text{mm}}{\text{rev}} \times 600 \, \frac{\text{rev}}{\text{min}} = 180 \, \frac{\text{mm}}{\text{min}} \] 4. Calculate the total drilling time (\(T_m\)): \[ T_m = \frac{L}{f_m} = \frac{36 \, \text{mm}}{180 \, \text{mm/min}} = 0.2 \, \text{minutes} \] Step 4: Final Answer:
Rounding off to two decimal places as requested, the total time is 0.20 minutes.