1. In NC part programming spindle speed of 730 rpm will be coded by the magic 3 rule as
(a) S673
(b) S730
(c) S630
(d) S037
(1 Mark, 1989)

Ans: b
In CNC programming, the number specified after ‘S’ indicates the spindle speed in rpm.
2. Numerically controlled machine tools are better suited for ____ (batch/ mass) production, because their setup time is ____ (larger/ smaller) in comparision to special purpose machine tools.
(1 Mark, 1991)

Ans: batch, larger
Special purpose machine tools are used for mass production.
3. In a pointtopoint type of NC system
(a) Control of position and velocity of the tool is essential
(b) Control of only position of the tool is sufficient
(c) Control of only velocity of the tool is sufficient
(d) Neither position nor velocity need to be controlled
(1 Mark, 1992)

Ans: b
In NC system, only end points of movement of tool is important but the path followed by the tool in between the points is not important. So, control of velocity of the tool is not essential.
4. With reference to NC machines, which of the following statements is wrong?
(a) Both closedloop and openloop control systems are used
(b) Paper tapes, floppy tapes and cassettes are used for data storage
(c) Digitizers may be used as interactive input devices
(d) Post processor is an item of hardware
(2 Mark, 1993)

Ans: d
Post processor is a software (sub program) which converts graphical or nongraphical CAM software toolpath outcome into a specific NC control.
Post processor is independent of hardware.
5. CNC machines are more accurate than conventional machines because they have a high resolution encoder and digital readouts for positioning. (T/F)
(1 Mark, 1994)

Ans: True
6. CNC machines are more economical to use even for simple turning jobs.(T/F)
(1 Mark, 1994)

Ans: False
CNC machines are not economical. So, they are used for producing complicated jobs in batch production.
7. In a point to point control NC machine, the slides are positioned by an integrally mounted stepper motor drive. If the specification of the motor is 1°/pulse, and the pitch of the lead screw is 3.6 mm, what is the expected positioning accuracy?
(a) 1 μm
(b) 10 μm
(c) 50 μm
(d) 100 μm
(2 Mark, 1997)

Ans: b
1 revolution of motor = 360^{0} of rotation
=> 1 revolution of motor = 360 pulses……..(1)
Again, 1 revolution of motor = Lead screw rotate 1 revolution
=> 1 revolution of motor = lead screw travel 1 pitch = 3.6 mm……(2)
From (1) and (2), 360 pulses = 3.6 mm
=> 1 pulse = 3.6/360 = 10 microns
The positioning accuracy is the distance traveled by the lead screw by 1 pulse.
9. In computer aided drafting practice, an arc is defined by
(a) Two end points only
(b) Centre and radius
(c) Radius and one end point
(d) Two end points and centre
(1 Mark, 2000)

Ans: d
option ‘d’ is correct.
10. In finish machining of an island on a casting with CNC milling machine, an end mill with 10 mm diameter is employed. The corner points of the island are represented by (0,0), (0,30), (50,30) and (50,0). By applying cutter radius right compensation, the trajectory of the cutter will be
(a) (5,0), (5,35), (55,35), (55,5), (5,5)
(b) (0,5), (55,5), (55,35), (5,35), (5,5)
(c) (5,5), (5,25), (45,25), (45,5), (5,5)
(d) (5,5), (45,5), (45,25), (5,25), (5,5)
(2 Mark, 2000)
11. Machining of complex shapes on CNC machines requires
(a) Simultaneous control of x, y and z axes
(b) Simultaneous control of x and y axes
(c) Independent control of x and y axes
(d) Independent control of x, y and z axes
(1 Mark, 2002)

Ans: a
Option ‘a’ is correct.
12. During the execution of a CNC part program block
NO20 GO2 X45.0 Y25.0 R5.0 the type of tool motion will be
(a) Circular Interpolation – clockwise
(b) Circular Interpolation – counter clock
(c) Linear Interpolation
(d) Rapid feed
(1 Mark, 2004)

Ans: a
G01: Linear Interpolation
G02: Circular Interpolation, ClockWise
G03: Circular Interpolation, CounterClockWise
13. In a 2D CAD package, clockwise circular arc of radius, 5, specified from P_{1} (15,10) to P_{2} (10,15) will have its centre at
(a) (10, 10)
(b) (15, 10)
(c) (15, 15)
(d) (10, 15)
(2 Mark, 2004)
14. Which among the NC operations given below are continuous path operations?
Arc Welding (AW), Milling (M), Drilling (D), Punching in Sheet Metal (P), Laser Cutting of Sheet Metal (LC), Spot Welding (SW)
(a) AW, LC and M
(b) AW, D, LC and M
(c) D, LC, P and SW
(d) D, LC and SW
(1 Mark, 2005)

Ans: a
Option ‘a’ is correct.
15. The tool of an NC machine has to move along a circular arc from (5,5) to (10,10) while performing an operation. The centre of the arc is at (10,5). Which one of the following NC tool path commands performs the above mentioned operation?
(a) N010 G02 X10 Y10 X5 Y5 R5
(b) N010 G03 X10 Y10 X5 Y5 R5
(c) N010 G01 X5 Y5 X10 Y10 R5
(d) N010 G02 X5 Y5 X10 Y10 R5
(2 Mark, 2005)
16. NC contouring is an example of
(a) Continuous path positioning
(b) Pointtopoint positioning
(c) Absolute positioning
(d) Incremental positioning
(1 Mark, 2006)

Ans: a
Option ‘a’ is correct.
17. Which type of motor is NOT used in axis or spindle drives of CNC machine tools?
(a) Induction motor
(b) DC servo motor
(c) Stepper motor
(d) Linear servo motor
(1 Mark, 2007)

Ans: a
Option ‘a’ is correct.
18. For generating a Coon’s surface we require
(a) A set of grid points on the surface
(b) A set of grid control points
(c) Four bounding curves defining the surface
(d) Two bounding curves and a set of grid control points
(1 Mark, 2008)

Ans: c
Option’c’ is correct.
(a) P – 2, Q – 3, R – 4, S – 1
(b) P – 3, Q – 4, R – 1, S – 2
(c) P – 3, Q – 4, R – 2, S – 1
(d) P – 4, Q – 3, R – 2, S – 1
(2 Mark, 2009)

Ans: c
Option ‘c’ is correct.
Statement for Linked Answer Questions 20 and 21:
In the feed drive of a Pointtopoint open loop CNC drive, a steeper motor rotating at 200 steps/rev drives a table through a gear box and lead screw – nut mechanism (pitch = 4mm, number of starts =1). The gear ratio \left( =\frac { Output\quad rotational\quad speed }{ Input\quad rotational\quad speed } \right) is given by U = 1/4. The stepper motor (driven by voltage pulses from a pulse generator) executes 1 step/ pulse of the pulse generator. The frequency of the pulse train from the pulse generator is f = 10,000 pulses per minute.
20. The Basic Length Unit (BLU), i.e. , the table movement corresponding to 1 pulse of the pulse generator, is
(a) 0.5 microns
(b) 5 microns
(c) 50 microns
(d) 500 microns
(2 Mark, 2008)

Ans: b
Basic length unit (BLU) = table movement corresponding to 1 pulse of the pulse generator = table movement corresponding to 1 step revolution of stepper motor
Revolution of motor in 1 step = \frac { 1 }{ 200 } rev/step
Rotational movement of lead screw = \frac { 1 }{ 200 } \times \frac { 1 }{ GR } = \frac { 1 }{ 200 } \times \frac { 1 }{ 4 } =\frac { 1 }{ 800 } rev
Movement of table = \frac { 1 }{ 800 } \times p=\frac { 1 }{ 800 } \times 4 = 0.005 mm = 5 microns
21. A customer insists on a modification to change the BLU the CNC drive to 10 microns without changing the table speed. The modification can be accomplished by
(a) Changing U to 1/2 and reducing f to \frac { f }{ 2 }.
(b) Changing U to 1/8 and increasing f to 2f.
(c) Changing U to 1/2 and keeping f unchanged
(d) Keeping U unchanged and increasing f to 2f.
(2 Mark, 2008)

Ans: c
If changing the U to 1/2 and keeping f unchanged,
then BLU = \frac { 1 }{ 200 } \times \frac { 1 }{ 2 } \times 4 = 10 microns
22. In a CNC program block, N002 G02 G91 X40 Z40…, G02 and G91 refer to
(a) Circular interpolation in counterclockwise direction and incremental dimension
(b) Circular interpolation in counterclockwise direction and absolute dimension
(c) Circular interpolation in clockwise direction and incremental dimension
(d) Circular interpolation in clockwise direction and absolute dimension
(1 Mark, 2010)

Ans: c
Option ‘c’ is correct.
24. For machining a rectangular island represented by coordinates P(0,0), Q(100,0), R(100,50) and S(0,50) on a casting using CNC milling machine, an end mill with a diameter of 16 mm is used. The trajectory of the cutter centre to machine the island PQRS is
(a) (−8, −8), (108, −8), (108,58), (−8,58), (−8, −8)
(b) (8,8), (94,8), (94,44), (8,44), (8,8)
(c) (−8,8), (94,0), (94,44), (8,44), (−8,8)
(d) (0,0), (100,0), (100,50), (50,0), (0,0)
(1 Mark, 2014[1])
25. A robot arm PQ with end coordinates P(0,0) and Q(2,5) rotates counter clockwise about P in the XY plane by 90°. The new coordinate pair of the end point Q is
(a) (−2,5)
(b) (−5,2)
(c) (−5, −2)
(d) (2, −5)
(1 Mark, 2014[2])
27. The function of interpolator in a CNC machine controller is to
(a) Control spindle speed
(b) Coordinate feed rates of axes
(c) Control tool rapid approach speed
(d) Perform Miscellaneous (M) functions (tool change, coolant control etc.)
(1 Mark, 2015[1])

Ans: b
Option ‘b’ is correct.
28. A triangular facet in a CAD model has vertices: P_{1}(0,0,0), P_{2}(1,1,0) and P_{3}(1,1,1). The area of the facet is
(a) 0.500
(b) 0.707
(c) 1.414
(d) 1.732
(2 Mark, 2015[1])
29. In a CNC milling operation, the tool has to machine the circular arc from point (20, 20) to (10, 10) at sequence number 5 of the CNC part program. If the center of the arc is at (20, 10) and the machine has incremental mode of defining position coordinates, the correct tool path command is
(a) N 05 G90 G01 X−10 Y−10 R10
(b) N 05 G91 G03 X−10 Y−10 R10
(c) N 05 G90 G03 X20 Y20 R10
(d) N 05 G91 G02 X20 Y20 R10
(2 Mark, 2015[3])
30. A drill is positioned at point P and it has to proceed to point Q. The coordinates of point Q in the incremental system of defining position of a point in CNC part program will be
(a) (3, 12)
(b) (5, 7)
(c) (7, 12)
(d) (4, 7)
(1 Mark, 2015[3])

Ans: d
In incremental system, Coordinate of Q: (4, 7)
In absolute system, Coordinate of Q: (7, 12)
31. Match the following part programming codes with their respective functions.
(a) P – II, Q – I, R – IV, S – III
(b) P – IV, Q – II, R – III, S – I
(c) P – IV, Q – III, R – II, S – I
(d) P – III, Q – IV, R – II, S – I
(1 Mark, 2016[3])

Ans: c
Option ‘c’ is correct.
32. Circular arc on a part profile is being machined on a vertical CNC milling machine, CNC part program using metric units with absolute dimensions is listed below:
………………………
N60 G01 X 30 Y 55 Z 5 F50
N70 G02 X 50 Y 35 R 20
N80 G01 Z 5
…………………………
The coordinates of the centre of the circular arc are:
(a) (30, 55)
(b) (50, 55)
(c) (50, 35)
(d) (30, 35)
(2 Mark, 2017[1])
33. Interpolator in a CNC machine
(a) Controls spindle speed
(b) Coordinates axes movements
(c) Operates tool changer
(d) Commands canned cycle
(1 Mark, 2018[1])

Ans: b
Option ‘b’ is correct.