First article inspection in CNC Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a basic CNC probing cycle

What is the output of the following CNC probing cycle command sequence when the probe touches the part surface at Z=5.0?

CNC Programming

G38.2 Z-10 F100
#100=0
IF [#100 EQ 0] THEN
  #101=5.0
ENDIF
PRINT #101

A 5.0

B 0

C 10

D Error: Undefined variable #101

💡 Hint

The probe sets a variable when it touches the surface; check the IF condition.

The probing command G38.2 moves the probe until it touches the surface at Z=5.0. The variable #100 is set to 0 indicating success, so #101 is assigned 5.0 and printed.

📝 Syntax

intermediate

Identify the syntax error in macro variable assignment

Which option contains a syntax error in assigning a macro variable in CNC code?

A #200=100

B #201:=200

C #202= #200 + 50

D #203= [#201 * 2]

💡 Hint

Check the assignment operator used in CNC macro variables.

In CNC macro programming, the assignment operator is '=', not ':='. Option B uses ':=' which is invalid syntax.

🔧 Debug

advanced

Why does this probing macro fail to update the variable?

Given the following macro code, why does the variable #300 remain zero after execution?

CNC Programming

G38.2 Z-20 F50
IF [#100 NE 0] THEN
  #300 = #101
ENDIF

A The feed rate F50 is too slow to trigger the probe

B The variable #101 is not assigned by the probe command

C The condition should check if #100 equals 0, not not equal to 0

D The macro syntax requires parentheses around the condition

💡 Hint

Check the meaning of the probe success variable #100.

The probe command sets #100 to 0 on success. The condition checks for not equal to 0, so the assignment never happens. It should check if #100 equals 0.

🚀 Application

advanced

Calculate the offset for first article inspection

You run a probing cycle to find the surface at Z=12.5. The nominal programmed Z is 10.0. Which option correctly calculates the offset to adjust the program for the next run?

A offset = 12.5 - 10.0

B offset = 10.0 + 12.5

C offset = 12.5 + 10.0

D offset = 10.0 - 12.5

💡 Hint

Offset is actual surface minus programmed surface.

The offset is the difference between the actual measured surface (12.5) and the programmed surface (10.0), so offset = 12.5 - 10.0 = 2.5.

🧠 Conceptual

expert

What is the main purpose of first article inspection in CNC automation?

Choose the best description of the main purpose of first article inspection in CNC automated machining.

A To clean the machine tools before starting production

B To speed up the machining process by skipping quality checks

C To calibrate the CNC machine's spindle speed automatically

D To verify the initial part dimensions match the design before full production

💡 Hint

Think about quality control at the start of production.

First article inspection ensures the first part made matches design specs, preventing errors in full production runs.