CNC Revision 1 of 3

According to The Provision & Use of Work Equipment Regulations 1998 (PUWER), when assessing the risks of an automatic tool changer, what is the most effective control measure to implement?

• Ensuring operators wear appropriate tight-fitting clothing and have received training.
• Fitting a securely fixed guard with a sensitive interlocking mechanism on the access door.
• Placing clear warning signs on the machine exterior and providing annual refresher training.
• Implementing a safe system of work where operators must remain at the control panel during tool changes.

A CNC machine's primary safety interlock on the main door fails, resulting in an open circuit. What is the most likely and correct "fail-safe" outcome of this specific fault?

• The machine will continue to operate with the doors open, presenting an immediate hazard.
• The machine will stop and be unable to initiate a cycle, even with the doors closed, until the fault is rectified.
• The machine's axes will automatically return to the machine reference point and then power down.
• An audible alarm will sound to warn the operator, but the current cycle will be allowed to complete.

A component blueprint specifies a high-precision internal bore (H6 tolerance) on a case-hardened steel part. Which CNC process is most suitable for the finishing operation?

• CNC Milling with a boring head.
• CNC Electro-Discharge Machining (EDM).
• CNC Grinding.
• CNC Turning with a cermet insert.

A programmer uses G41 for cutter radius compensation on an external profile. The finished part is consistently undersized by an amount equal to the tool's diameter. What is the most probable cause of this error?

• The tool's diameter was entered in the offset register instead of its radius.
• The tool path was programmed for climb milling, but G42 (for conventional milling compensation) should have been used.
• The feed rate was too high for the depth of cut, causing significant tool deflection.
• The G41 command was activated on the same program block as a Z-axis movement.

Why is it considered poor practice to program a G00 (rapid traverse) move involving simultaneous X, Y, and Z axis changes when approaching a workpiece?

• A G00 move disables the spindle, which may need to be running for the next operation.
• The axes move at their individual maximum speeds, resulting in a non-linear "dog-leg" path that is hard to predict and could cause a collision.
• The combined power draw of three axes moving at maximum speed can trip the machine's circuit breaker.
• Rapid traverse moves do not check for feedback from the encoders, leading to positioning errors.

Calculate a suitable spindle speed (rpm) for turning a 48 mm diameter steel bar, if the recommended cutting speed is 210 m/min.

• 2785 rpm
• 1393 rpm
• 8750 rpm
• 700 rpm

Calculate the correct feed rate in mm/min for a 4-flute end mill with a recommended chip load of 0.05 mm/tooth, rotating at 1500 rpm.

• 75 mm/min
• 120 mm/min
• 300 mm/min
• 600 mm/min

During setup, an operator "touches off" a new end mill to the top surface of the workpiece (Z0) and records the value in the work offset register (e.g., G54). What is the direct purpose of this action?

• To calibrate the absolute position of the machine's Z-axis encoder.
• To measure the length of the tool for the tool offset page.
• To establish the relationship between the machine coordinate system and the program's Z-axis datum.
• To ensure the workpiece is sitting perfectly flat on the machine bed or in the vice.

When using a controller's graphic simulation, what type of potential problem is it LEAST likely to identify?

• Incorrect surface finish due to excessive tool vibration or "chatter".
• A rapid traverse move (G00) that passes through a work-holding clamp.
• The final machined profile not matching the component drawing.
• A collision between the tool holder and the workpiece during a deep pocketing routine.