MILLING

Technical Tips

45-degree Face Mill vs. a 90-degree Face Mill.

To achieve greater productivity and problem-free milling, use a lead angle cutter whenever possible. Chip thickness is affected by the lead angle. The greater the lead angle, the greater the chip-thinning effect.

Advantages

  • Well-balanced axial and radial cutting forces.
  • Less breakout on workpiece corner.
  • Entry shock is minimized.
  • Less radial forces directed into the spindle bearings.
  • Higher feed rates possible.
  • Reduces chatter.

Disadvantages

  • Reduced maximum depth of cut due to lead angle.
  • Larger body diameter can cause fixture clearance problems.
  • No 90-degree corner milling.
  • Can cause chipping or burring on exit side of cutter rotation.

Reducing Chatter & Vibration in End Milling

When chatter occurs, it can be self-sustaining until the problem is corrected. Chatter causes poor finish on the part, and will damage and significantly reduce the life of end mills. Carbide end mills are particularly susceptible to damage.

Typical methods to reduce chatter include reducing cutting forces by:

  1. Reducing the number of flutes.
  2. Decreasing the chipload per tooth by reducing the feed or increasing the speed or RPM.
  3. Reducing the axial or radial depth of cut.
  4. Though these steps will reduce chatter, slowing down the cutting process is not always the best course of action, and reducing the chipload can be detrimental to the cutter.

Better first steps are to improve rigidity and stability:

  1. Use a larger end mill with a larger core diameter.
  2. Use end mills with reduced clearance or a small circular margin.
  3. Use the shortest overhang from spindle nose to tip of tool.
  4. Use stub length end mills where possible.
  5. Use balanced tool holders.
  6. Rework fixture to hold the workpiece more securely.
  7. Reprogram the cutter path to shift cutting forces into stiffer portions of the workpiece.
  8. Look for ways to improve spindle speeds then adjust feed accordingly.

Chatter is common when machining corners. As the end mill enters the corner, the percentage of engagement increases the number of teeth in the cut. This drastically increases the cutting forces, causing chatter.

To reduce chatter when machining corners, consider using circular interpolation to produce a bigger corner radius than indicated by the part print. Then remove the remaining stock with a smaller end mill using circular interpolation.

Reducing Chatter in End Milling

Chatter in the form of vibration and noise is a frequent challenge when end milling, causing scalloping and uneven finishes.

To reduce chatter, try the following:

  • Ensure that the starting places for speeds and feeds are correct for the workpiece material and the cut.
  • Increase the feed, or chipload per tooth/tool.
  • Make the workpiece as secure and rigid as possible.
  • Reduce excess overhang between the workpiece and spindle.
  • Select an end mill with more flutes.
  • Check the tool run-out.
  • Review the tool geometry to ensure the cutting face, relief, fluting and helix angle are appropriate for the workpiece material.
  • If conventional milling, try climb milling.

Understanding Milling Insert Nomenclature

  1. First station indicates shape of insert.
  2. Second station shows relief angle or rake angle of the insert.
  3. The third station provides a working gage for repeatability. It sets tolerance to the I.C. (inscribed circle) and creates a gage tolerance for the I.C. to the over-the-nose radius along with the thickness of the insert.
  4. Fourth station indicates geometry and clamping insert type. It designates with or without hole, shape and size of hole, chipbreaker form, and single- or double-sided insert.
  5. Fifth station indicates I.C. size of the insert.
  6. Sixth station designates insert thickness.
    T = 1/16” inch increments
  7. Seventh station designates corner configuration of the insert.
  8. Cutting edge form
    F for sharp
    E For Honed edge
    T for T-Land
    S for Honed T-Land
  9. Designates N for neutral, R for right-handed, or L for left-handed insert.
  10. Designates facet width of insert.
    2 – .0312”
    3 – .0469”
    4 – .0625”
    6 – .0938”
  11. Edge prep size
    L – Light sharp or lightly honed or T-landed
    G – General Medium hone and/or T-land
    H – Heavy – large hone and/or T-land
  12. Rake face angle
    Angle on insert prior to installation.
    N – 0 degree, A – 3 degree, B – 5 degree, C – 7 degree, P – 11 degree,
    D- 15 degree, E – 20 degree, F – 25 degree, G – 30 degree.
  13. Added Info
    J – polished rake face
    P – partial T-land
    W- Wiper Insert