Conditional statements (IF-THEN) in CNC Programming - Step-by-Step Execution

Concept Flow - Conditional statements (IF-THEN)

Start

↓

Evaluate Condition

↓

Execute THEN block

No↓

Skip THEN block

↓

Continue Program

The CNC program checks a condition. If true, it runs the THEN commands; if false, it skips them and continues.

Execution Sample

CNC Programming

IF [#100 GT 50] THEN
  G01 X10 Y10
ENDIF

If variable #100 is greater than 50, move tool to X10 Y10.

Execution Table

Step	Condition Checked	Condition Result	Action Taken	Output/Movement
1	#100 GT 50	True	Execute THEN block	Move tool to X10 Y10
2	End of IF	N/A	Continue program	No further action

💡 Condition true, THEN block executed; program continues after IF.

Variable Tracker

Variable	Start	After Step 1	Final
#100	60	60	60

Key Moments - 2 Insights

Why does the program move the tool only when #100 is greater than 50?

Because the condition '#100 GT 50' is checked at Step 1 in the execution_table. If true, the THEN block runs, moving the tool.

What happens if the condition is false?

The THEN block is skipped, so no movement occurs. This is shown by the 'Skip THEN block' path in concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table, what is the action taken when the condition '#100 GT 50' is true?

A Execute THEN block and move tool to X10 Y10

B Skip THEN block and do nothing

C Stop the program

D Reset variable #100

💡 Hint

Check Step 1 in execution_table under 'Action Taken' column.

At which step does the program continue after the IF statement?

A Step 1

B Before Step 1

C Step 2

D Never continues

💡 Hint

Look at Step 2 in execution_table where action is 'Continue program'.

If #100 was 40 instead of 60, how would the execution_table change?

A Condition Result would be True and THEN block executed

B Condition Result would be False and THEN block skipped

C Program would stop with error

D Variable #100 would change to 50

💡 Hint

Refer to key_moments about what happens if condition is false.

Concept Snapshot

IF-THEN checks a condition.
If true, runs THEN commands.
If false, skips THEN commands.
Syntax: IF [condition] THEN ... ENDIF
Used to control CNC tool actions based on variables.

Full Transcript

In CNC programming, conditional statements let the machine decide what to do based on conditions. The IF-THEN statement checks if a condition is true. For example, if variable #100 is greater than 50, the machine moves the tool to X10 Y10. If not, it skips that move. This helps make programs smarter and adaptable. The flow starts by evaluating the condition, then either runs the commands inside THEN or skips them, continuing the program. Variables like #100 hold values that affect decisions. Understanding this helps control CNC machines precisely.

Practice

1. What does an IF-THEN statement do in CNC programming?

easy

A. It repeats a set of commands multiple times.

B. It stops the machine immediately.

C. It defines the speed of the machine.

D. It makes the program choose actions based on conditions.

Solution

1. Step 1: Understand the purpose of IF-THEN

   IF-THEN checks a condition and runs commands only if the condition is true.

2. Step 2: Compare with other options

   Repeating commands is done by loops, speed is set by other commands, and stopping is a different command.

3. Final Answer:

   It makes the program choose actions based on conditions. -> Option D

4. Quick Check:

   IF-THEN controls flow based on conditions [OK]

Hint: IF-THEN means "if this, then do that" [OK]

Common Mistakes:

• Confusing IF-THEN with loops
• Thinking IF-THEN sets machine speed
• Assuming IF-THEN stops the machine

2. Which of the following is the correct syntax for an IF statement in CNC programming?

easy

A. WHEN condition DO
commands
END

B. IF (condition) {
commands
}

C. IF [condition] THEN
commands
ENDIF

D. if condition:
commands

Solution

1. Step 1: Identify CNC IF syntax

   CNC uses IF [condition] THEN ... ENDIF structure.

2. Step 2: Check other options

   Options B and C use programming languages like C or Python syntax, A is not standard CNC syntax.

3. Final Answer:

   IF [condition] THEN commands ENDIF -> Option C

4. Quick Check:

   CNC IF syntax uses THEN and ENDIF [OK]

Hint: Look for THEN and ENDIF keywords in CNC IF syntax [OK]

Common Mistakes:

• Using parentheses or braces like other languages
• Omitting THEN or ENDIF keywords
• Confusing IF with WHEN or DO

3. What will be the output of this CNC code snippet?

IF #100 GT 50 THEN
  #101 = 1
ELSE
  #101 = 0
ENDIF
PRINT #101

Assuming variable #100 is 60.

medium

A. 0

B. 1

C. Syntax Error

D. No output

Solution

1. Step 1: Evaluate the condition #100 GT 50

   #100 is 60, which is greater than 50, so condition is true.

2. Step 2: Determine the assigned value to #101

   Since condition is true, #101 is set to 1, then printed.

3. Final Answer:

   1 -> Option B

4. Quick Check:

   60 > 50 is true, so #101 = 1 [OK]

Hint: Check condition truth to find which branch runs [OK]

Common Mistakes:

• Confusing GT (greater than) with LT (less than)
• Ignoring ELSE branch
• Assuming syntax error due to ELSE

4. Identify the error in this CNC IF statement:

IF #200 EQ 10
  G01 X100 Y100
ENDIF

medium

A. Missing THEN keyword after condition

B. Incorrect variable name #200

C. Missing ENDIF keyword

D. G01 command is invalid inside IF

Solution

1. Step 1: Check IF statement syntax

   CNC IF requires THEN after the condition, missing here.

2. Step 2: Verify other parts

   Variable name is valid, ENDIF is present, G01 is valid command inside IF.

3. Final Answer:

   Missing THEN keyword after condition -> Option A

4. Quick Check:

   IF must have THEN before commands [OK]

Hint: IF condition must be followed by THEN [OK]

Common Mistakes:

• Forgetting THEN after IF condition
• Thinking ENDIF is missing
• Assuming commands can't be inside IF

5. You want the CNC machine to move to X=50 only if the tool number (#1) is 3 or higher. Which IF statement correctly does this?

hard

A. IF #1 GE 3 THEN
G01 X50
ENDIF

B. IF #1 GT 3 THEN
G01 X50
ENDIF

C. IF #1 LE 3 THEN
G01 X50
ENDIF

D. IF #1 EQ 3 THEN
G01 X50
ENDIF

Solution

1. Step 1: Understand the condition "3 or higher"

   This means #1 is greater than or equal to 3 (GE 3).

2. Step 2: Check each option's condition

   IF #1 GE 3 THEN G01 X50 ENDIF uses GE (greater or equal), B uses GT (greater than) which excludes 3, C uses LE (less or equal), D uses EQ (equal only).

3. Final Answer:

   IF #1 GE 3 THEN G01 X50 ENDIF -> Option A

4. Quick Check:

   GE means "3 or higher" [OK]

Hint: Use GE for "greater or equal" conditions [OK]

Common Mistakes:

• Using GT excludes the value 3
• Using LE or EQ does not cover all values 3 or higher
• Confusing GE with GT