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What is fz in Machining?

Published in Machining Parameters 3 mins read

fz in machining represents the feed per tooth, which is the distance the cutting tool advances into the workpiece for each tooth or cutting edge that passes.

In simpler terms, imagine a milling cutter with multiple teeth spinning around. fz tells you how far forward the entire cutter moves for each tooth that engages with the material being cut. It's a crucial parameter for controlling the machining process.

Here's a breakdown:

  • Definition: Feed per tooth (fz) is the linear distance traveled by the cutting tool during one revolution per tooth. It's typically measured in millimeters per tooth (mm/tooth) or inches per tooth (in/tooth).

  • Importance: fz significantly impacts:

    • Surface Finish: A smaller fz generally results in a smoother surface finish.
    • Cutting Forces: A larger fz increases cutting forces, potentially leading to tool deflection, vibration, and poor surface finish.
    • Chip Formation: fz influences the shape and size of the chips produced during machining.
    • Tool Life: Using an appropriate fz can optimize tool life. Too high, and you risk rapid wear or breakage; too low, and you might induce rubbing, which also damages the tool.
    • Material Removal Rate (MRR): Increasing fz can increase the MRR, allowing for faster machining. However, this must be balanced with the other factors mentioned above.

  • Calculation: The feed per tooth is related to the table feed rate (vf), the number of teeth on the cutter (z), and the spindle speed (n) by the following formula:

    vf = fz * z * n

    Where:

    • vf = Table feed rate (mm/min or in/min)
    • fz = Feed per tooth (mm/tooth or in/tooth)
    • z = Number of teeth on the cutter
    • n = Spindle speed (RPM - Revolutions Per Minute)

    Therefore:

    fz = vf / (z * n)

  • Example: If a milling cutter has 8 teeth (z = 8) and a feed per tooth (fz) of 0.2 mm/tooth, and the spindle speed is 1000 RPM, then the table feed rate (vf) would be:

    vf = 0.2 mm/tooth 8 teeth 1000 RPM = 1600 mm/min

  • Selection Considerations: Selecting the optimal fz depends on several factors, including:

    • Workpiece Material: Different materials require different feed rates.
    • Tool Material: The tool's material composition influences its ability to withstand cutting forces and heat.
    • Cutting Tool Geometry: The shape and design of the cutting tool affect its cutting performance.
    • Machine Tool Capabilities: The machine's rigidity and power influence the achievable feed rates.
    • Desired Surface Finish: The required surface quality impacts the appropriate feed rate.
    • Cutting Depth & Width: Larger cuts usually need lower feed rates to prevent excessive loads.

Choosing the correct fz is a balancing act that requires experience and knowledge of machining principles to achieve optimal performance, tool life, and surface finish.

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