Preventing Part Movement During CNC Machining

DALIAN, China - July 13, 2025 - PRLog -- Why Do Parts Move During CNC Machining?
Several forces act on a part during machining—most notably the cutting force generated by the tool engaging with the material. If the workholding system is not strong or precise enough to counteract these forces, or if improper setup is used, the part may shift slightly or significantly.
Common causes include:
Inadequate or uneven clamping force
Poor fixture design or incorrect fixturing for the part geometry
Vibrations or chatter due to machine instability
Incorrect alignment or setup error
Thermal expansion or material deflection during cutting
Risks and Consequences of Part Movement
Even the slightest movement during cutting can lead to:

Loss of dimensional accuracy
Surface finish degradation
Out-of-tolerance features or failed QA inspections
Broken tools or damaged fixtures
Increased scrap rate and production delays
In high-precision industries like aerospace or medical manufacturing, part stability is non-negotiable. Machining a high-value part with improper fixturing can lead to major financial losses or safety risks.

Best Practices to Prevent Part Movement During CNC Machining
1. Select the Right Workholding System
Not all parts require a vise. Depending on geometry, size, and material, better options may include:

Soft jaws or custom-machined jaws that conform to irregular shapes
Fixture plates with dowel pins for repeatable location
Vacuum fixtures for thin or non-rigid parts
Magnetic workholding for ferrous components
Collet chucks for round bar stock or turned parts
Ensure the selected method is appropriate for both clamping force and accessibility of the cutting area.

2. Apply Uniform Clamping Pressure
Unbalanced clamping leads to tilting, vibration, or movement during cutting. Use torque-limiting tools or calibrated systems to apply consistent pressure across multiple clamps or fasteners. For large parts, distribute clamps evenly across the surface to avoid bowing or distortion.

3. Use Dowel Pins or Locating Stops
Clamping alone isn't enough. Clamps apply pressure but do not define position—especially under lateral cutting forces. Dowel pins, hardened stops, or precision shoulders should be used to mechanically constrain the part and absorb shear forces.

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