Parting off operation in CNC Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a simple parting off G-code snippet

What is the output behavior of this CNC program snippet for parting off?

N10 G00 X20 Z2
N20 G01 Z-10 F0.1
N30 G00 X100

CNC Programming

N10 G00 X20 Z2
N20 G01 Z-10 F0.1
N30 G00 X100

A The tool rapidly moves to X20 Z-10, then cuts in Z to 2 at feed 0.1, then retracts rapidly to X100

B The tool moves slowly to X20 Z2, then rapidly cuts to Z-10, then moves slowly to X100

C The tool rapidly moves to X20 Z2, then cuts straight in Z to -10 at feed 0.1, then retracts rapidly to X100

D The tool rapidly moves to X100 Z2, then cuts straight in Z to -10 at feed 0.1, then retracts rapidly to X20

💡 Hint

Remember G00 is rapid move, G01 is linear feed move with specified feed rate.

G00 moves the tool rapidly to the specified coordinates without cutting. G01 moves the tool linearly at the feed rate, performing the cut. So the tool first moves rapidly to X20 Z2, then cuts in Z to -10 at feed 0.1, then retracts rapidly to X100.

🧠 Conceptual

intermediate

Purpose of feed rate in parting off operation

Why is setting the correct feed rate important during a parting off operation in CNC programming?

A To control the cutting speed and avoid tool breakage or poor surface finish

B To make the tool move faster than the spindle speed

C To ensure the tool does not move at all during cutting

D To change the spindle rotation direction automatically

💡 Hint

Think about what happens if the tool moves too fast or too slow while cutting.

The feed rate controls how fast the tool moves through the material. If too fast, the tool can break or the finish will be rough. If too slow, it wastes time and can cause tool wear. Correct feed rate balances speed and quality.

🔧 Debug

advanced

Identify the error in this parting off G-code

What error will this G-code cause during a parting off operation?

N10 G00 X5 Z0
N20 G01 Z-15 F0.05
N30 G01 X0 F0.1

CNC Programming

N10 G00 X5 Z0
N20 G01 Z-15 F0.05
N30 G01 X0 F0.1

A There is no error; the code runs correctly

B The feed rate is too high causing tool breakage

C The spindle speed is missing causing a runtime error

D The tool will crash into the chuck because it moves to X0 after cutting

💡 Hint

Consider the tool position after the cut and the machine setup.

Moving the tool to X0 after cutting can cause it to crash into the chuck or fixture because X0 is usually the centerline. The tool should retract safely away from the part.

🚀 Application

advanced

Calculate the number of passes for parting off

A parting off tool cuts 2 mm deep per pass. The stock diameter is 20 mm. How many passes are needed to part off completely?

A 10 passes

B 20 passes

C 5 passes

D 15 passes

💡 Hint

Divide the total diameter by the depth per pass.

Each pass cuts 2 mm deep. To cut through 20 mm diameter, 20 / 2 = 10 passes are needed.

💻 Command Output

expert

Output of a complex parting off G-code with canned cycle

What is the output behavior of this G-code snippet using a canned cycle for parting off?

N10 G71 P20 Q30 U0.5 W0.2 F0.1
N20 G00 X15 Z2
N30 G01 Z-12
N40 G00 X100

CNC Programming

N10 G71 P20 Q30 U0.5 W0.2 F0.1
N20 G00 X15 Z2
N30 G01 Z-12
N40 G00 X100

A The tool moves slowly to X100 before cutting

B The G71 canned cycle performs roughing passes between lines 20 and 30 with stock allowance, then the tool retracts rapidly

C The G71 command causes a syntax error and the program stops

D The tool moves rapidly to X15 Z2, then cuts directly to Z-12 without roughing passes

💡 Hint

G71 is a rough turning cycle that uses P and Q to define start and end blocks.

G71 is a rough turning canned cycle. It repeats roughing passes between blocks N20 and N30 with stock allowances U and W. After finishing, the tool retracts rapidly to X100.

Practice

1. What is the main purpose of a parting off operation in CNC turning?

easy

A. To drill holes in the workpiece

B. To cut a finished piece from the raw stock

C. To polish the surface of the workpiece

D. To measure the length of the stock

Solution

1. Step 1: Understand the definition of parting off

   Parting off is a CNC turning process used to separate a finished part from the raw material.

2. Step 2: Identify the correct operation purpose

   Among the options, only cutting a finished piece from raw stock matches the parting off operation.

3. Final Answer:

   To cut a finished piece from the raw stock -> Option B

4. Quick Check:

   Parting off = Cutting finished piece [OK]

Hint: Parting off always means cutting off the finished part [OK]

Common Mistakes:

• Confusing parting off with drilling or polishing
• Thinking parting off measures stock length
• Assuming parting off smooths surfaces

2. Which of the following is the correct G-code command to start a parting off operation with feed rate control?

easy

A. G71 X20 Z-5 F0.1

B. G00 X20 Z-5 F0.1

C. G71 X20 Z-5 S1000

D. G01 X20 Z-5

Solution

1. Step 1: Identify G-code for parting off with feed rate

   G01 is the linear interpolation command used for controlled feed moves, including parting off, with feed rate control.

2. Step 2: Check options for correct syntax

   G01 X20 Z-5 moves the tool linearly to X20 Z-5 at the current feed rate. G71 is for rough turning cycles, not typically used for simple parting off moves with feed rate control.

3. Final Answer:

   G01 X20 Z-5 -> Option D

4. Quick Check:

   G01 = linear feed move for parting off [OK]

Hint: G01 is used for feed controlled linear moves like parting off [OK]

Common Mistakes:

• Using G00 which is rapid move, not cutting
• Omitting feed rate (F) in parting off
• Confusing spindle speed (S) with feed rate (F)

3. Given the following CNC code snippet for parting off:

G71 X15 Z-3 F0.05
G00 X20 Z0
G71 X15 Z-3 F0.05

What will be the final position of the tool after execution?

medium

A. X15 Z-3

B. X15 Z0

C. X20 Z0

D. X20 Z-3

Solution

1. Step 1: Analyze the G-code sequence

   The first G71 command moves tool to X15 Z-3 with feed. Then G00 moves tool rapidly to X20 Z0.

2. Step 2: Identify final tool position

   The last command G71 X15 Z-3 F0.05 moves the tool to X15 Z-3 with feed. Thus, final position is X15 Z-3.

3. Final Answer:

   X15 Z-3 -> Option A

4. Quick Check:

   Last G71 to X15 Z-3 [OK]

Hint: Final position from last command execution [OK]

Common Mistakes:

• Stopping analysis after the G00 rapid move
• Ignoring the final G71 command
• Confusing rapid positioning with final cut position

4. Identify the error in this parting off CNC code snippet:

G71 X10 Z-2 F
G00 X15 Z0

medium

A. Missing feed rate value after F

B. Incorrect use of G00 command

C. Wrong axis letter used

D. Spindle speed not set

Solution

1. Step 1: Check G71 command syntax

   G71 requires feed rate value after F. Here, F is present but no value is given.

2. Step 2: Verify other commands

   G00 command is correct for rapid move. Axis letters X and Z are valid. Spindle speed is optional here.

3. Final Answer:

   Missing feed rate value after F -> Option A

4. Quick Check:

   F must have a value [OK]

Hint: Always provide a value after F for feed rate [OK]

Common Mistakes:

• Leaving F without a number
• Confusing G00 with cutting move
• Thinking spindle speed is mandatory here

5. You want to part off a piece with a diameter of 30 mm and length 5 mm using G71. Which command correctly sets the tool path for this operation?

hard

A. G71 X30 Z-5 F0.08

B. G71 X15 Z5 F0.08

C. G71 X15 Z-5 F0.08

D. G71 X30 Z5 F0.08

Solution

1. Step 1: Convert diameter to radius for X-axis

   In CNC turning, X value is radius, so diameter 30 mm means X=15 mm.

2. Step 2: Set Z-axis for length and direction

   Length 5 mm is negative Z direction for parting off, so Z=-5.

3. Step 3: Confirm feed rate and syntax

   Feed rate F0.08 is valid. So command is G71 X15 Z-5 F0.08.

4. Final Answer:

   G71 X15 Z-5 F0.08 -> Option C

5. Quick Check:

   X=radius=15, Z=-5 length, feed set [OK]

Hint: X is radius (half diameter), Z negative for parting off length [OK]

Common Mistakes:

• Using diameter instead of radius for X
• Setting Z positive instead of negative
• Omitting feed rate or using wrong sign