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Cutting Parameters and Speeds/Feeds Flashcards

7 cards from real CNC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. What is the correct formula for calculating spindle speed (RPM) from cutting speed (SFM) and tool diameter (D in inches)?

    Answer: RPM = (SFM × 12) / (π × D)

    RPM = (SFM × 12) / (π × D) converts linear cutting speed to rotational speed by accounting for the tool's circumference in inches.

  2. In CNC milling, what does 'feed rate' primarily describe?

    Answer: The linear distance the cutting tool travels per unit of time (inches per minute)

    Feed rate in milling is typically expressed as inches per minute (IPM), describing how fast the cutter moves through the workpiece material.

  3. 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.

  4. What is 'chip load' (feed per tooth) in CNC milling?

    Answer: The amount of material each cutting edge removes per revolution

    Chip load (feed per tooth) is the thickness of the chip each flute removes per revolution, calculated as IPM / (RPM × number of flutes).

  5. When switching from machining steel to aluminum, cutting speeds (SFM) should typically:

    Answer: Increase significantly because aluminum is much softer and thermally conductive

    Aluminum can be machined at 3–5× higher SFM than steel because it is softer, has excellent thermal conductivity, and does not require the same heat management.

  6. What problem most commonly results from setting the milling feed rate too low?

    Answer: Tool rubbing rather than cutting, causing work hardening and increased tool wear

    An excessively low feed rate causes the cutter to rub the surface rather than shear it, generating heat that work hardens the material and dulls the tool prematurely.

  7. 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.