CNC Revision 3 of 3

When would a programmer choose to use a floating datum (e.g., G55) in addition to the primary fixed datum (G54)?

• When programming in incremental mode instead of absolute.
• When machining multiple identical parts mounted in separate vices on the machine table.
• When the part is too large to be defined by a single datum point.
• When using a sub-program to perform a repetitive task.

A Coordinate Measuring Machine (CMM) is used to inspect a first-off component and the results are fed back into the CNC machine's controller. This is an example of what?

• Statistical Process Control (SPC).
• Reverse Engineering.
• Adaptive Control.
• Preventative Maintenance.

A thin-walled aluminium component needs to be machined on a CNC mill. Which work-holding strategy would be most appropriate to prevent the part from distorting under clamping pressure?

• A standard machine vice tightened to the maximum torque.
• Large G-clamps applied directly to the top surface of the part.
• Double-sided tape.
• A custom vacuum chuck or a fixture with multiple points of support and minimal clamping force.

A machine operator notices that aluminium components are coming off the machine with a poor, "smeared" surface finish and material is sticking to the tool's cutting edge. The coolant concentration is tested and found to be very low. Why would this cause the issue?

• Insufficient lubrication from the low oil-to-water ratio is causing a built-up edge (BUE) on the tool.
• The low concentration is causing the machine to rust, which is contaminating the workpiece.
• The coolant is not providing sufficient cooling, causing the aluminium to become too hard to cut cleanly.
• The low concentration changes the coolant's viscosity, altering the programmed feed rate.

A CNC machine is suffering from backlash in the X-axis, which is noticeable as a small step or inaccuracy when changing direction (e.g., milling a circle). What is the most likely mechanical cause of this issue?

• A lack of lubrication on the linear guide rails.
• Wear in the ballscrew nut or thrust bearings.
• A loose connection on the X-axis servo motor's power cable.
• Incorrect parameters in the control for motor acceleration.

When would a programmer choose to write a user-defined sub-program instead of using a built-in canned cycle?

• For simple drilling operations, as sub-programs are easier to write than canned cycles.
• For a complex, unique pocketing routine or hole pattern that is repeated multiple times on the same part.
• When the machine control does not support standard canned cycles like G81 or G83.
• When programming in incremental mode, as canned cycles only work in absolute mode.

What is the key difference in machine behaviour between an M01 (Optional Stop) and an M00 (Program Stop)?

• M00 stops the spindle and coolant, whereas M01 only stops axis movement.
• M00 is ignored by the control unless the operator has pressed a specific button first.
• M01 is only acted upon if the "Optional Stop" button on the control panel is active; M00 will always stop the machine.
• M01 resets the program to the beginning, while M00 just pauses it.

The machine's current absolute position is X10.0, Y20.0. The program commands an incremental move to drill a hole: G91 G01 X-40.0 Y-50.0;. What is the absolute coordinate of the hole?

• X-40.0 Y-50.0
• X50.0 Y70.0
• X-30.0 Y-30.0
• X-50.0 Y-70.0

A job requires a deep slot to be milled in titanium. Which tooling characteristic would be the most critical for success in this application?

• High toughness and good chip evacuation.
• Extreme hardness and a very sharp cutting edge.
• A multi-flute design (e.g., 10 flutes) for a high feed rate.
• A general-purpose coating like Titanium Nitride (TiN).

If an operator incorrectly enters a tool radius value in the wear offset register instead of the geometry register, what is the likely consequence?

• The initial cut will be incorrect, and any subsequent wear adjustments will be added to this already incorrect value, compounding the error.
• The machine will not use the value, as wear offsets are typically very small incremental values.
• The control will automatically move the value from the wear to the geometry register.
• It will have no effect on the part size, but it may cause an alarm.