Mixed Deck — All CNC Topics Flashcards

Which of the following best describes the purpose of a CNC machine's soft limits?

Answer: They are software boundaries that prevent axis travel beyond a safe range

Soft limits are programmable boundaries set in the CNC controller that stop axis motion before it reaches hard mechanical stops or causes a crash.

An automated CNC mailer would have

Answer: Countering control

An automated CNC machine, particularly one capable of complex machining operations, requires contouring control. Contouring control allows the machine to move multiple axes simultaneously and in a coordinated manner to generate intricate curves and surfaces. This is essential for producing complex shapes and profiles, unlike point-to-point control which only moves to specific coordinates without controlled path generation between them.

Which type of milling cutter is used to machine a flat surface perpendicular to the spindle axis?

Answer: Face mill

A face mill has cutting inserts arranged on its face and periphery, specifically designed to machine large flat surfaces quickly and efficiently.

What type of clamping error occurs when a workpiece is 'overconstrained' in a fixture?

Answer: Locating contact points compete, causing distortion or inconsistent seating

Overconstraining (or redundant locating) creates competing contact points that can distort the part or cause inconsistent seating, leading to location errors.

What does Ra measure in surface finish inspection?

Answer: The arithmetic average roughness of the surface profile

Ra is the arithmetic mean of the absolute values of the profile deviations from the mean line, providing an average roughness value for the surface.

In high-production CNC machining, what is a pallet changer used for?

Answer: Exchanging workpiece pallets so setup occurs while the machine is cutting

A pallet changer lets operators load and unload parts on one pallet while the machine cuts parts on another, dramatically reducing machine idle time.

In high-speed machining (HSM), which parameter change most defines the strategy compared to conventional machining?

Answer: Cutting speed (SFM) is significantly increased, often paired with lighter radial engagement

HSM is characterized by very high cutting speeds (SFM), often combined with reduced RDOC and appropriate chip load adjustments to maintain manageable cutting forces and tool life.

What is the purpose of an automatic tool length measurement (TLM) probe in a CNC machining center?

Answer: To automatically measure and store each tool's length offset after a tool change

A tool length measuring probe touches the tip of each tool and records its actual length in the offset table, eliminating manual tool-setting and ensuring accurate Z-axis positioning.

What role does a CNC machine's spindle orientation (M19) command play in safe tool changes?

Answer: It locks the spindle at a fixed angular position so the tool key aligns correctly

M19 orients and locks the spindle at a precise angle to ensure the tool-holder key aligns with the spindle drive slots during automatic or manual tool changes.

Which of these won't contribute to ensuring machine safety?

Answer: Multi-tasking

Multi-tasking, especially when operating machinery, significantly reduces focus and attention to detail, thereby increasing the risk of accidents. Safe machine operation requires undivided attention to the task at hand, constant monitoring of the machine's operation, and awareness of potential hazards. Distractions caused by multi-tasking can lead to errors, injuries, or damage to equipment, directly compromising machine safety.

What is 'chatter' in CNC machining and what is its primary cause?

Answer: Vibration between the tool and workpiece caused by resonance in the cutting system

Chatter is self-excited vibration where the cutting forces feed energy into the machine-tool-workpiece resonant frequency, producing poor surface finish and accelerated tool wear.

In precision measurement, what does 'gauge R&R' study evaluate?

Answer: The repeatability and reproducibility of a measurement system

Gauge R&R (Repeatability and Reproducibility) studies determine how much of the measurement variation comes from the gauge itself versus the parts being measured.

A CNC operator is performing a dry run (no material) to verify a new program. What is the safest practice?

Answer: Use single-block mode and reduced feed rate override

Single-block mode lets the operator review each line of code step by step, and a reduced feed override provides time to react to unexpected motion.

Which factor most directly accelerates tool wear rate in CNC cutting?

Answer: Higher cutting speed (SFM)

Higher cutting speeds generate more heat at the cutting edge, which exponentially accelerates tool wear according to Taylor's tool life equation.

Which body part is most commonly injured by CNC machine operations according to occupational safety data?

Answer: Hands and fingers from contact with tools, chips, or pinch points

Hands and fingers are the most frequently injured body parts in CNC operations due to contact with sharp tools, flying chips, and pinch points during setup and loading.

What does a negative Cpk value indicate about a manufacturing process?

Answer: The process mean is outside one of the specification limits

A negative Cpk means the process average has moved beyond one of the specification limits, indicating that a significant portion of parts are being produced out of tolerance.

In end milling, 'axial depth of cut' (ADOC) refers to:

Answer: How far the cutting flutes engage the workpiece along the tool's Z-axis

Axial depth of cut is the depth of engagement measured along the tool's axis (Z-direction), controlling what length of the flute contacts the material.

The tapping cycle on a machine center is displayed using the G code, which is

Answer: G89

In CNC programming, G-codes are used to prepare the machine for specific types of motion or operations. G89 is the standard G-code specifically designated for a tapping cycle that includes a dwell at the bottom of the hole. Other G-codes like G81, G82, and G83 are used for various drilling cycles, which are distinct from tapping operations.

What is the function of a toe clamp in CNC fixturing?

Answer: To hold the workpiece from above by stepping over its edge

Toe clamps step over the edge of a workpiece and apply downward clamping force from above, holding the part to the table or fixture plate.

What is the primary purpose of ball screw lubrication in a CNC machine?

Answer: To reduce friction, prevent wear, and maintain positioning accuracy of the linear axes

Ball screw lubrication reduces friction between balls and raceways, prevents wear, dissipates heat, and maintains the tight positioning accuracy required for precision machining.