CNC Revision 2 of 3

A first-off inspection report notes that all diameters are correct, but the positional true-position tolerance of a pattern of holes is out of specification. What does this most likely indicate?

• An error in the programmed coordinates for the hole locations or an incorrect work offset (datum).
• The wrong tool was used for drilling the holes.
• The spindle speed was too low, or the feed rate was too high.
• The material does not conform to the specified grade.

During a manual tool change on a CNC mill, after stopping the spindle, the operator presses the tool release button, but the tool does not release. What is the most likely cause related to the machine's systems?

• Insufficient air pressure to the pneumatic cylinder that actuates the drawbar.
• A fault in the M06 (tool change) macro program.
• The tool has become welded into the spindle taper due to excessive heat.
• The machine's hydraulic pump is turned off.

Which statement best evaluates the trade-offs between CNC and manually operated equipment for producing a batch of 50 complex, identical components?

• Manual is preferable due to lower setup time; CNC is too slow to program for only 50 parts.
• CNC is preferable as it requires less skilled labour, although the material cost will be higher.
• CNC is ideal due to its high repeatability and ability to produce complex geometries, justifying the higher initial programming time and machine cost.
• Manual is better as it allows for on-the-fly adjustments to each part, resulting in higher overall quality.

How does a closed-loop CNC system respond when a discrepancy is detected between the programmed position and the actual axis position reported by the encoder?

• It immediately stops the program and displays a generic "servo alarm".
• The control sends a correcting signal to the servo motor to eliminate the position error in real-time.
• It logs the error but allows the program to continue, potentially causing inaccuracies.
• It automatically reduces the programmed feed rate by 50% to try and improve accuracy.

A program for a CNC mill with a 20-station Automatic Tool Changer (ATC) calls for Tool 21. What will be the machine's response?

• The machine will use Tool 20, the closest available tool.
• The machine will use Tool 1, as the carousel will loop back to the beginning.
• The machine will stop and generate an alarm as the requested tool is out of the defined range.
• The machine will pause and wait for the operator to manually load Tool 21.

A CNC program block reads: N50 G90 G01 X100.0 Y50.0 F150;. If the previous block set an M05 (Spindle Stop), what will happen when this block is run?

• The axes will move in a straight line to X100.0 Y50.0, but no cutting will occur as the spindle is not running.
• The machine will generate an error because a G01 move requires an active spindle speed.
• The G90 code will automatically restart the spindle before the axes move.
• The block will be skipped as M05 is a modal command that deactivates all subsequent movement.

A G54 work offset has the value Z-250.5 stored in its register. The tool length offset for the active tool is H01, which is 150.0 mm. If the program commands G00 Z10.0;, where will the tool tip move to in the machine's own coordinate system?

• Z-90.5
• Z-100.5
• Z160.0
• Z-240.5

A program uses incremental coordinates (G91) to drill a series of four holes. The first move is G91 G01 X20.0 F100;. If this exact block is repeated three more times, what will be the absolute coordinate of the fourth hole, assuming the start point was X0?

• X20.0
• X40.0
• X60.0
• X80.0

Which of these methods would be the most effective way of proving-out a complex 5-axis surfacing program to ensure no over-cutting or gouging of the workpiece occurs?

• Using third-party verification software (e.g., Vericut) that simulates the exact machine kinematics and removes material from a stock model.
• Running the program 500mm above the job in the Z-axis to visually check the tool path.
• Machining the part from a soft material like high-density foam or wax.
• Using the machine's built-in graphic simulation to view the tool path from different angles.