Subprogram call (M98) and return (M99) in CNC Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call a subprogram with number 100.

CNC Programming

M[1] P100

Drag options to blanks, or click blank then click option'

A97

B99

C100

D98

Attempts:

3 left

💡 Hint

Common Mistakes

Using M99 to call a subprogram instead of returning from it.

Using a number other than 98 to call the subprogram.

M98 is the command used to call a subprogram in CNC programming.

2fill in blank

medium

Complete the code to return from a subprogram.

CNC Programming

M[1]

Drag options to blanks, or click blank then click option'

A99

B98

C97

D100

Attempts:

3 left

💡 Hint

Common Mistakes

Using M98 to return instead of calling the subprogram.

Using a number other than 99 to return.

M99 is the command used to return from a subprogram in CNC programming.

3fill in blank

hard

Fix the error in the subprogram call command.

CNC Programming

M[1] P200

Drag options to blanks, or click blank then click option'

A100

B97

C98

D99

Attempts:

3 left

💡 Hint

Common Mistakes

Using M99 to call a subprogram.

Using an invalid code like 100 or 97.

M98 is the correct command to call a subprogram; other codes are incorrect here.

4fill in blank

hard

Fill both blanks to call subprogram 150 and then return from it.

CNC Programming

M[1] P150
M[2]

Drag options to blanks, or click blank then click option'

A98

B99

C97

D100

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping M98 and M99 commands.

Using incorrect numbers like 97 or 100.

M98 calls the subprogram and M99 returns from it.

5fill in blank

hard

Fill all three blanks to call subprogram 120 three times.

CNC Programming

M[1] P120 L[2]
M[3]

Drag options to blanks, or click blank then click option'

A98

B3

C99

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong repeat count.

Using M99 to call instead of return.

Omitting the repeat count.

M98 calls the subprogram, L specifies repeat count, M99 returns from subprogram.

Practice

1. What does the M98 command do in CNC programming?

easy

A. Stops the machine immediately

B. Ends the current subprogram and returns to the main program

C. Starts the spindle rotation

D. Calls a subprogram by its number, optionally repeating it

Solution

1. Step 1: Understand the role of M98

   The M98 command is used to call a subprogram by its number and can repeat it multiple times if specified.

2. Step 2: Differentiate from M99

   M99 is used to end a subprogram and return to the main program, not to call it.

3. Final Answer:

   Calls a subprogram by its number, optionally repeating it -> Option D

4. Quick Check:

   M98 calls subprogram [OK]

Hint: M98 calls subprogram; M99 returns from it [OK]

Common Mistakes:

• Confusing M98 with M99
• Thinking M98 stops the machine
• Assuming M98 starts spindle

2. Which of the following is the correct syntax to call subprogram number 100 with 3 repetitions?

easy

A. M100 P98 L3

B. M98 P100 L3

C. M98 L3 P100

D. M99 P100 L3

Solution

1. Step 1: Identify correct M98 syntax

   The correct syntax to call a subprogram is M98 followed by P (program number) and optionally L (repeat count), so M98 P100 L3 is correct.

2. Step 2: Check other options for errors

   M99 is for return, not call; order matters; M100 is not a command.

3. Final Answer:

   M98 P100 L3 -> Option B

4. Quick Check:

   Call syntax = M98 P100 L3 [OK]

Hint: M98 P[number] L[repeat] calls subprogram [OK]

Common Mistakes:

• Using M99 instead of M98 to call
• Swapping P and L parameters
• Using invalid command like M100

3. Given this CNC program snippet:

N10 M98 P200 L2
N20 M30

O200
N10 G01 X10 Y10
N20 M99

What will happen when the program runs?

medium

A. The subprogram 200 runs twice, then the main program ends

B. The subprogram 200 runs once, then the main program loops infinitely

C. The program will cause a syntax error at M99

D. The main program ends immediately without running subprogram

Solution

1. Step 1: Analyze M98 call with L2

   M98 P200 L2 calls subprogram 200 two times.

2. Step 2: Understand M99 in subprogram

   M99 ends the subprogram and returns to main program after each call.

3. Step 3: Main program ends with M30

   After subprogram calls, M30 ends the main program.

4. Final Answer:

   The subprogram 200 runs twice, then the main program ends -> Option A

5. Quick Check:

   M98 L2 calls twice, M99 returns, M30 ends [OK]

Hint: M98 with L repeats subprogram; M99 returns to main [OK]

Common Mistakes:

• Thinking M99 causes error
• Assuming infinite loop without M99
• Ignoring L parameter repeat count

4. Identify the error in this CNC code snippet:

N10 M98 P300
N20 M30

O300
N10 G01 X20 Y20
N20 M30

medium

A. Subprogram 300 does not have M99 to return

B. M98 command is missing the repeat count L

C. Main program should not have M30

D. Subprogram number should be 200, not 300

Solution

1. Step 1: Check subprogram termination

   Subprogram 300 ends with M30, which ends the entire program, not returns to main.

2. Step 2: Identify missing M99

   Subprograms must end with M99 to return control to main program after call.

3. Final Answer:

   Subprogram 300 does not have M99 to return -> Option A

4. Quick Check:

   Missing M99 causes no return from subprogram [OK]

Hint: Subprograms must end with M99 to return [OK]

Common Mistakes:

• Using M30 inside subprogram instead of M99
• Thinking L parameter is mandatory
• Confusing subprogram number

5. You want to machine 5 identical pockets using subprogram 150. Which code snippet correctly calls the subprogram 5 times and returns properly?

hard

A. N10 M98 P150 L5
N20 M99

O150
N10 G01 X0 Y0
N20 M99

B. N10 M98 P150
N20 M99

O150
N10 G01 X0 Y0
N20 M30

C. N10 M98 P150 L5
N20 M30

O150
N10 G01 X0 Y0
N20 M99

D. N10 M98 P150 L5
N20 M30

O150
N10 G01 X0 Y0
N20 M30

Solution

1. Step 1: Confirm main program calls subprogram 5 times

   M98 P150 L5 calls subprogram 150 five times, correct for repetition.

2. Step 2: Check subprogram ends with M99

   Subprogram ends with M99 to return control after each call.

3. Step 3: Main program ends with M30

   M30 properly ends the main program after calls.

4. Final Answer:

   N10 M98 P150 L5
   N20 M30
   
   O150
   N10 G01 X0 Y0
   N20 M99 -> Option C

5. Quick Check:

   M98 with L5 and M99 in subprogram [OK]

Hint: Use M98 P[number] L5 and M99 to return [OK]

Common Mistakes:

• Ending subprogram with M30 instead of M99
• Using M99 in main program instead of M30
• Omitting repeat count L5