Depth of cut and step-over in CNC Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Calculate total passes for depth of cut

A CNC program sets a total depth of cut of 12 mm with a depth of cut per pass of 3 mm. How many passes will the machine make to complete the cut?

A 4

B 6

C 3

D 5

💡 Hint

Divide total depth by depth per pass.

Total passes = total depth / depth per pass = 12 / 3 = 4 passes.

💻 Command Output

intermediate

Calculate step-over distance in a CNC milling operation

If the tool diameter is 10 mm and the step-over is set to 40% of the tool diameter, what is the step-over distance?

A 6 mm

B 2.5 mm

C 4 mm

D 5 mm

💡 Hint

Step-over = tool diameter × step-over percentage.

Step-over distance = 10 mm × 0.4 = 4 mm.

📝 Syntax

advanced

Identify the correct G-code for setting depth of cut

Which of the following G-code lines correctly sets a depth of cut of 5 mm in a CNC milling program?

A G01 Z5.0 F100

B G01 Z-5.0 F100

C G00 Z-5.0 F100

D G00 Z5.0 F100

💡 Hint

G01 is linear feed move; negative Z moves down.

G01 moves the tool linearly at feed rate; Z-5.0 moves down 5 mm for cutting.

🚀 Application

advanced

Calculate total machining time with depth of cut and step-over

A CNC milling operation uses a tool diameter of 8 mm, step-over of 50%, depth of cut per pass of 10 mm, and total depth of 10 mm. The feed rate is 200 mm/min and the cut length per pass is 100 mm. How long will the machining take (in minutes), assuming only linear cutting time?

A 12.5 minutes

B 25 minutes

C 50 minutes

D 20 minutes

💡 Hint

Calculate passes for depth, passes for step-over, then total passes and time.

Depth passes = 10/10 = 1; step-over passes = 100/(8*0.5) = 25; total passes = 1*25=25; time = (25*100)/200 = 12.5 minutes.

🔧 Debug

expert

Find the error in this CNC depth of cut loop script

This pseudo-code loops through depth passes but produces an infinite loop. What is the error? ``` depth = 10 depth_per_pass = 2 current_depth = 0 while current_depth < depth: print(f"Cutting at depth {current_depth} mm") ```

CNC Programming

depth = 10
depth_per_pass = 2
current_depth = 0
while current_depth < depth:
    print(f"Cutting at depth {current_depth} mm")

A The depth_per_pass variable should be initialized to zero.

B The comparison operator should be <= instead of < in the while condition.

C The print statement syntax is incorrect and causes a runtime error.

D The variable current_depth is never updated inside the loop, causing an infinite loop.

💡 Hint

Check if the loop variable changes inside the loop.

Without updating current_depth inside the loop, the condition never becomes false, causing an infinite loop.

Practice

1. What does the depth of cut control in CNC machining?

easy

A. How fast the tool moves along the path

B. How deep the tool cuts into the material each pass

C. The speed of the spindle rotation

D. The temperature of the cutting tool

Solution

1. Step 1: Understand depth of cut meaning

   Depth of cut means how far down the tool goes into the material per pass.

2. Step 2: Match with options

   How deep the tool cuts into the material each pass matches this definition exactly, others describe different parameters.

3. Final Answer:

   How deep the tool cuts into the material each pass -> Option B

4. Quick Check:

   Depth of cut = tool depth per pass [OK]

Hint: Depth of cut = vertical cut depth per pass [OK]

Common Mistakes:

• Confusing depth of cut with feed rate
• Mixing depth of cut with spindle speed
• Thinking depth of cut controls sideways movement

2. Which of the following is the correct way to specify a step-over of 0.5 mm in a CNC program line?

easy

A. STEP_OVER 0.5

B. STEP_OVER = 0.5

C. STEP_OVER(0.5)

D. STEP_OVER:0.5

Solution

1. Step 1: Identify common CNC parameter syntax

   CNC programs often use keyword followed by value without symbols for parameters.

2. Step 2: Compare options

   STEP_OVER 0.5 uses keyword and value separated by space, which is standard. Others use symbols not typical in CNC code.

3. Final Answer:

   STEP_OVER 0.5 -> Option A

4. Quick Check:

   Parameter syntax = keyword + space + value [OK]

Hint: Parameters usually use space, not symbols, between name and value [OK]

Common Mistakes:

• Adding equals sign or parentheses incorrectly
• Using colon instead of space
• Confusing step-over syntax with programming languages

3. Given a CNC program snippet:

DEPTH_OF_CUT 2.0
STEP_OVER 1.0
MILLING_PASS

What will be the depth and sideways move per pass?

medium

A. Depth 1.0 mm, Step-over 2.0 mm

B. Depth 1.0 mm, Step-over 1.0 mm

C. Depth 2.0 mm, Step-over 2.0 mm

D. Depth 2.0 mm, Step-over 1.0 mm

Solution

1. Step 1: Read parameter values

   DEPTH_OF_CUT is set to 2.0 mm, STEP_OVER is set to 1.0 mm.

2. Step 2: Match values to depth and step-over

   Depth of cut = 2.0 mm, step-over = 1.0 mm as per the program lines.

3. Final Answer:

   Depth 2.0 mm, Step-over 1.0 mm -> Option D

4. Quick Check:

   DEPTH_OF_CUT=2.0, STEP_OVER=1.0 [OK]

Hint: Match parameter names to values directly [OK]

Common Mistakes:

• Swapping depth and step-over values
• Ignoring parameter names and guessing
• Assuming default values instead of given

4. A CNC program uses DEPTH_OF_CUT 3.0 and STEP_OVER 1.5 but the tool only cuts 1.5 mm deep per pass. What is the likely error?

medium

A. The machine overrides depth to 1.5 mm for safety

B. The step-over value is too large and limits depth

C. The depth of cut parameter is ignored due to syntax error

D. The tool diameter is smaller than depth of cut

Solution

1. Step 1: Analyze parameter effect

   If depth of cut is set to 3.0 but actual cut is 1.5, likely the program did not apply 3.0 correctly.

2. Step 2: Consider syntax errors

   A syntax error in the depth of cut line can cause the machine to ignore it and use default or previous value (1.5).

3. Final Answer:

   The depth of cut parameter is ignored due to syntax error -> Option C

4. Quick Check:

   Syntax error causes parameter ignore [OK]

Hint: Check syntax if parameters don't apply as expected [OK]

Common Mistakes:

• Blaming step-over for depth issues
• Assuming machine overrides without checking code
• Ignoring syntax errors in program

5. You want to machine a 10 mm deep pocket with a tool that can safely cut 2 mm depth per pass and 40% step-over of its 5 mm diameter. How many passes and what step-over distance should you program?

hard

A. 5 passes, 2 mm step-over

B. 2 passes, 2 mm step-over

C. 5 passes, 2.5 mm step-over

D. 5 passes, 0.4 mm step-over

Solution

1. Step 1: Calculate number of passes

   Depth per pass = 2 mm, total depth = 10 mm, so passes = 10 / 2 = 5 passes.

2. Step 2: Calculate step-over distance

   Step-over = 40% of 5 mm diameter = 0.4 * 5 = 2 mm.

3. Final Answer:

   5 passes, 2 mm step-over -> Option A

4. Quick Check:

   Passes = 10/2=5, Step-over = 0.4*5=2 mm [OK]

Hint: Divide depth by cut depth; multiply diameter by step-over % [OK]

Common Mistakes:

• Confusing step-over percentage with depth
• Calculating passes incorrectly
• Using wrong tool diameter for step-over