Mixed Deck — All CNC Topics Flashcards

What is the function of M30 in a CNC program?

Answer: End program and return to start

M30 ends the program, rewinds to the beginning, and resets all modal states, readying the machine for the next run.

What is spindle speed measured in?

Answer: RPM

Spindle speed, which dictates how fast the cutting tool or workpiece rotates, is universally measured in Revolutions Per Minute (RPM). This measurement is a critical parameter in CNC machining, directly influencing the cutting speed, material removal rate, and surface finish. Proper RPM selection is essential for optimizing tool life and machining efficiency for different materials.

Which stainless steel family is generally non-magnetic and cannot be hardened by heat treatment?

Answer: Austenitic stainless steel

Austenitic stainless steels (300 series) retain their FCC crystal structure at room temperature, making them non-magnetic and hardenable only by cold working.

On a feature control frame reading ⌀0.005 M A B, what does the symbol M indicate?

Answer: Bonus tolerance is allowed as the feature departs from Maximum Material Condition

The MMC modifier (M) means bonus tolerance equal to the departure from MMC is added to the stated tolerance as the feature's actual size moves away from MMC.

In CNC programming, what does the G28 command instruct the machine to do?

Answer: Return to machine home (reference) position

G28 commands the machine to return to its machine home (reference zero) position, typically passing through an intermediate point for safety.

When a drawing calls for a 'ground' surface, which post-processing step is implied?

Answer: Cylindrical or surface grinding to achieve fine tolerance and finish

A 'ground' callout means the surface is finished by grinding, achieving tolerances and finishes beyond what turning or milling alone can produce.

What does the term 'regardless of feature size' (RFS) mean in modern ASME Y14.5-2009 and later standards?

Answer: The geometric tolerance applies at any produced size of the feature — no bonus tolerance is allowed

Under ASME Y14.5-2009, RFS is the default condition — geometric tolerances apply regardless of the feature's actual size unless MMC or LMC is explicitly invoked.

D2 tool steel is classified as a:

Answer: High-carbon, high-chromium cold work tool steel

D2 is a high-carbon (1.5% C), high-chromium (11-13% Cr) cold work tool steel known for excellent wear resistance.

Which measurement tool is BEST suited for checking the pitch diameter of an external thread?

Answer: Three-wire method with a micrometer

The three-wire method — inserting precisely sized wires into thread grooves and measuring over them with a micrometer — gives the most accurate direct pitch diameter measurement.

A CNC machinist measures a bore with an inside micrometer and gets 1.2503". The print calls for 1.2500" ±0.0003". What is the correct disposition?

Answer: Accept — within tolerance

1.2503" falls within the allowable range of 1.2497"–1.2503", so the part is acceptable.

When conducting a PM on a CNC turning center, why is it important to check the turret indexing repeatability?

Answer: Turret position accuracy directly affects the dimensional accuracy of turned parts

If the turret doesn't return to the exact same position each time, the cutting tool position changes, causing dimensional variation in machined parts.

What does a 'phantom line' (long-short-short dashed line) typically represent on a CNC blueprint?

Answer: Alternate positions of a moving part, repeated features, or the outline of adjacent parts

Phantom lines show alternate positions of movable parts, repeated detail patterns, or the envelope of adjacent/mating components.

A drill with a 118-degree point angle is considered standard. A 135-degree point angle is used for:

Answer: Hard materials and self-centering applications

The 135-degree split-point drill is designed for harder materials and provides better self-centering without a center punch.

Statistical Process Control (SPC) uses control charts to monitor a process. A process is considered 'out of control' when:

Answer: Any single point falls outside ±3 sigma control limits

A single point beyond the ±3 sigma (3σ) control limits is the primary Western Electric rule indicating an out-of-control condition.

A 'dead-length' collet system in a CNC lathe differs from a standard collet in that it:

Answer: Clamps the workpiece without axial movement, maintaining a fixed Z-datum position

Dead-length collets expand/contract radially without moving the workpiece axially, preserving the part's Z-axis position and eliminating datum shift.

What does SPC stand for in quality control?

Answer: Statistical Process Control

SPC stands for Statistical Process Control, which is a method used in quality control to monitor and control a process using statistical techniques. By collecting and analyzing data from a process, SPC helps identify variations, predict future performance, and ensure that the process remains within acceptable limits. This leads to consistent product quality and reduced defects.

What does an 'Rz' (Rzmax) measurement on a drawing indicate compared to Ra?

Answer: Rz is the average of the five highest peak-to-valley measurements; Ra is the overall arithmetic average

Rz averages the five largest peak-to-valley heights over the evaluation length, making it more sensitive to extreme surface events than Ra.

Which ANSI standard governs safety requirements for machining centers and automatic tool-change systems?

Answer: ANSI B11.8

ANSI B11.8 specifically addresses safety requirements for drilling, milling, and boring machines, including machining centers with ATC systems.

Which workholding method is most appropriate for CNC milling a thin, flat aluminum plate that cannot be clamped on the edges?

Answer: Double-sided tape or a vacuum fixture

Double-sided tape or a vacuum fixture holds the full underside of the plate without obstructing the top surface or bending thin material.

A GD&T feature control frame reads ⊙ | 0.005 | A | B. What does the ⊙ symbol indicate?

Answer: Position

The circle with a cross (⊙) is the GD&T symbol for Position, controlling the location of a feature relative to datums.