Parting off operation in CNC Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a parting off operation in CNC machining?

Parting off is a machining process where a cutting tool is used to cut off a finished part from the raw material or bar stock. It separates the workpiece from the remaining material.

beginner

Which tool is typically used for a parting off operation?

A parting tool or cutoff blade is used. It is a thin, narrow tool designed to cut through the material to separate the part cleanly.

intermediate

Why is it important to control feed rate during parting off?

Controlling feed rate prevents tool breakage and ensures a smooth cut. Too fast feed can cause tool damage; too slow can cause rubbing and poor finish.

beginner

What safety precautions should be taken during parting off?

Ensure the workpiece is securely clamped, use proper tool speed and feed, wear safety glasses, and keep hands clear of the cutting area.

intermediate

How does coolant help in a parting off operation?

Coolant reduces heat generated by cutting, improves tool life, and helps remove chips from the cutting area for a cleaner cut.

What is the main purpose of a parting off operation?

A To separate a finished part from raw material

B To drill holes in the workpiece

C To polish the surface

D To bend the metal

Parting off is used to cut off the finished part from the raw stock.

Which tool is best suited for parting off?

A Parting tool

B End mill

C Drill bit

D Face mill

A parting tool is specifically designed for cutting off parts.

What can happen if feed rate is too high during parting off?

A Coolant evaporates instantly

B Workpiece will polish

C Cutting speed decreases

D Tool may break

Too high feed rate can cause excessive force and break the tool.

Why is coolant used in parting off?

A To speed up the machine

B To reduce heat and remove chips

C To change the color of the metal

D To lubricate the operator's hands

Coolant helps keep the tool cool and clears chips for a better cut.

Which safety measure is important during parting off?

A Wear sandals

B Use maximum feed rate always

C Securely clamp the workpiece

D Keep hands on the tool

Clamping the workpiece prevents movement and accidents.

Explain the parting off operation and why it is important in CNC machining.

Think about how finished parts are separated from raw material.

Describe key safety and operational tips to follow during a parting off operation.

Consider what keeps the operator safe and the tool working well.

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