Day 10 CNC Machines – ECET 2026 Mechanical

Why this topic is important for ECET?

CNC (Computer Numerical Control) Machines are at the heart of modern manufacturing. In ECET exams, questions often test your understanding of CNC basics, axis conventions, programming codes, advantages, and applications. Knowing this topic gives you an edge since it directly connects theory with industry practices like automation, precision machining, and advanced production systems.

📘 Concept Notes

🔹 What is CNC?

CNC = Computer Numerical Control → A system where machine tool operations are controlled by programmed instructions (G-codes & M-codes).
Eliminates manual errors, increases speed & accuracy.

🔹 Basic Elements of CNC Machine

Input Device – For feeding program (Keyboard, USB, DNC system).
Machine Control Unit (MCU) – Brain of CNC, interprets the code.
Drive System – Motors (stepper/servo) that move axes.
Feedback System – Ensures correct motion (closed-loop control).
Machine Tool – Actual cutting tool performing machining.

🔹 CNC Axes Convention

2-Axis: X & Y movements.
3-Axis: X, Y, Z (milling, drilling).
4/5 Axis: Rotation about additional axes (used in aerospace, molds).

🔹 CNC Programming Basics

G-codes → Preparatory functions (motion commands). Example: G01 = linear interpolation, G02/G03 = circular interpolation.
M-codes → Miscellaneous functions (auxiliary). Example: M03 = spindle ON (CW), M05 = spindle OFF.

Example CNC Program (Milling):

N10 G90 G00 X0 Y0 Z5  
N20 G01 Z-2 F200  
N30 G01 X50 Y50 F300  
N40 M30

N10 G90 G00 X0 Y0 Z5  
N20 G01 Z-2 F200  
N30 G01 X50 Y50 F300  
N40 M30

🔹 Advantages of CNC

High accuracy and repeatability.
Complex shapes possible.
Reduces labor cost.
Easy automation.

🔹 Applications

Aerospace parts, Automobile components, Molds & Dies, Defense equipment.

⚙️ Formulas

Material Removal Rate (MRR):
$MRR = f \times d \times v$
where

fff = feed (mm/rev)
ddd = depth of cut (mm)
vvv = cutting speed (mm/min)

Spindle Speed (N):
$N = \frac{1000 \times V}{\pi \times D}$
where

VVV = cutting speed (m/min)
DDD = workpiece diameter (mm)

Feed Rate (Fr):
$Fr = N \times f \times z$
where

zzz = number of teeth (milling cutter)

🔟 10 MCQs

Q1. CNC stands for:
a) Central Numerical Control
b) Computer Numerical Control
c) Common Number Control
d) Coded Numerical Computing

Q2. Which part of CNC interprets the program and controls machine operation?
a) Drive system
b) MCU
c) Feedback system
d) Tool head

Q3. G-code G02 is used for:
a) Spindle ON
b) Clockwise circular interpolation
c) Counterclockwise circular interpolation
d) Return to home position

Q4. In CNC machines, M-codes represent:
a) Motion commands
b) Miscellaneous functions
c) Feed rate
d) Tool path

Q5. A CNC lathe operates at cutting speed 200 m/min with workpiece dia 50 mm. Find spindle speed NNN.
a) 1000 rpm
b) 1273 rpm
c) 1500 rpm
d) 2000 rpm

Q6. In CNC programming, absolute positioning uses:
a) Incremental coordinates
b) Reference to previous point
c) Reference to fixed origin
d) Random coordinates

Q7. Feedback in CNC ensures:
a) Tool sharpness
b) Correct tool path and position
c) Heat control
d) Machine lubrication

Q8. Which of the following is NOT an advantage of CNC?
a) High productivity
b) Complex shapes
c) High initial cost
d) Easy automation

Q9. The MRR in a turning operation is 0.2 mm/rev feed, 2 mm depth of cut, 500 mm/min speed. Calculate MRR.
a) 200 mm³/min
b) 300 mm³/min
c) 200 mm²/min
d) 500 mm³/min

Q10. A 3-axis CNC milling machine moves along:
a) X, Y only
b) X, Y, Z
c) X, Z only
d) X, Y, A

✅ Answer Key

Q	Ans
1	b
2	b
3	b
4	b
5	b
6	c
7	b
8	c
9	d
10	b

🧠 Explanations

Q1: CNC = Computer Numerical Control → (b).
Q2: MCU is the brain of CNC, controls motion → (b).
Q3: G02 = circular interpolation clockwise → (b).
Q4: M-codes handle miscellaneous (spindle, coolant, etc.) → (b).
Q5: $N = \frac{1000 \times V}{\pi D} = \frac{1000 \times 200}{\pi \times 50} \approx 1273$ rpm → (b).
Q6: Absolute = reference to fixed origin → (c).
Q7: Feedback ensures correct tool position → (b).
Q8: High initial cost is a disadvantage, not advantage → (c).
Q9: $MRR = f \times d \times v = 0.2 \times 2 \times 500 = 200$ mm³/min → (d).
Q10: 3-axis = X, Y, Z → (b).

🎯 Motivation / Why Practice Matters

CNC Machines are modern manufacturing backbone. In ECET, questions can be conceptual (codes, axes) or numerical (spindle speed, MRR). Practicing both types ensures you avoid silly mistakes and answer quickly under exam pressure. Remember – speed + accuracy = rank boost in ECET 2026.

📲 CTA

👉 Join our WHATSAPP group for ECET 2026 updates, discussions, and free practice materials:
https://chat.whatsapp.com/GniYuv3CYVDKjPWEN086X9

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Day 10 CNC Machines – ECET 2026 Mechanical

Why this topic is important for ECET?