456. A cylinder of 155 mm diameter is to be reduced to 150 mm diameter In one turning cut with a feed of 0.15 mm/rev and a cutting speed of 150 m/min on a NC lathe. What are the programmed feed rate and the material removal rate.

1. 1. 6250mm³/ min.

   
   
   

   2. 56250mm³/ min.

   
   
   

   3. 562mm³/ min.

   
   
   

   4. None of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   V = ωr = 2Nr.
   = πdN {2r = d, ω = 2πN}
   

   So, N =	V	⇒ N =	150 × 103	= 308 rpm.
   	πd		π × 155

   
   Programmed feed rate
   = f × N = 0.15 × 308 = 46.2 mm/rpm
   

   = f × V ×	(D2 − D1)	= 0.15 × 150 × 103 × 2.5
   	2

   
   = 56250mm³/ min.

   Correct Option: B

   V = ωr = 2Nr.
   = πdN {2r = d, ω = 2πN}
   

   So, N =	V	⇒ N =	150 × 103	= 308 rpm.
   	πd		π × 155

   
   Programmed feed rate
   = f × N = 0.15 × 308 = 46.2 mm/rpm
   

   = f × V ×	(D2 − D1)	= 0.15 × 150 × 103 × 2.5
   	2

   
   = 56250mm³/ min.

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457. In a point to point control NC machine, the slides positioned by an integrally mounted stepper motor drive. If the specification of the motor is 1 deg/pulse, and the pitch Of the lead screw is 3.6 mm.
     What is the expected positioning accuracy?

1. 1. 1 micron

   
   
   

   2. 10 micron

   
   
   

   3. 50 micron

   
   
   

   4. 100 micron

   
   
   

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1. View Hint View Answer Discuss in Forum

   For 1 revolution of lead screw side will move by 3.6 mm
   1 revolution = 360° = 360 pulses 360 pulses will cause motion of 3.6 mm. 1 pulse will result in 3.6/360 mm of motion
   i.e. 0.01 mm or 10 µm.

   Correct Option: B

   For 1 revolution of lead screw side will move by 3.6 mm
   1 revolution = 360° = 360 pulses 360 pulses will cause motion of 3.6 mm. 1 pulse will result in 3.6/360 mm of motion
   i.e. 0.01 mm or 10 µm.

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458. CNC machines are more economical to use even for simpie turning jobs. (T/F)

1. 1. False

   
   
   

   2. True

   
   
   

   3. T/F

   
   
   

   4. None of the above

   
   
   

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1. View Hint View Answer Discuss in Forum

   False

   Correct Option: A

   False

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459. CNC machines are more accurate than conventional machines because they have a high resolution encoder and digital readouts for positioning. (T/F)
     

1. 1. True

   
   
   

   2. False

   
   
   

   3. T/F

   
   
   

   4. None of the above

   
   
   

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1. View Hint View Answer Discuss in Forum

   True

   Correct Option: A

   True

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460. With reference to NC machine, which of the following statement is wrong?

1. 1. Both closed loop and open loop control systems are used

   
   
   

   2. Paper tapes, floppy drives and cassettes are used for data Storage

   
   
   

   3. Digitisers may be used as interactive input devices

   
   
   

   4. Post-processor is an item of hardware

   
   
   

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1. View Hint View Answer Discuss in Forum

   Post-Processor is not used in NC machine.

   Correct Option: D

   Post-Processor is not used in NC machine.

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