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Slide 002: End Milling — Slots, Pockets, and Profiles

Slide Visual

End Milling — Slots, Pockets, and Profiles

Slide Overview

This slide covers end milling operations including edge finding, slot cutting, pocket milling, and profile machining using various end mill types.

Instruction Notes

Edge Finding (Work Coordinate Setup)

Before cutting, you must establish where the workpiece edges are relative to the spindle. The edge finder (wobble finder) is the standard tool:

  1. Install the edge finder in a collet. Set spindle speed to 800-1200 RPM.
  2. Move the table so the edge finder's lower half approaches the workpiece edge.
  3. The lower half wobbles as it spins. When it contacts the edge and aligns with the upper half, it will suddenly "kick" sideways—this is the touch point.
  4. At the kick point, the spindle center is exactly 0.100" (edge finder radius) from the workpiece edge.
  5. Zero the dial collar or DRO axis. Move 0.100" toward the workpiece to position the spindle center exactly on the edge.
  6. Re-zero. This is your X=0 (or Y=0) reference.
  7. Repeat for the perpendicular edge if needed.

End Mill Types

Type Flutes Center Cutting Best For
Square end mill 2-4 2-flute: yes; 4-flute: check Slots, shoulders, general work
Ball end mill 2-4 Yes 3D contours, fillets, radii
Corner radius end mill 4 Varies Strong corners, reduced stress risers
Roughing end mill 4-6 No Heavy material removal

Slot Cutting

A slot is a groove cut fully into the workpiece. The end mill must be center-cutting if plunging to start the slot.

Procedure: 1. Select an end mill equal to or smaller than the desired slot width. 2. Edge-find to locate the slot center position. 3. Set the Z-depth (DOC per pass): 0.5× cutter diameter maximum for steel, 1× diameter for aluminum. 4. Lock Y-axis. Feed X-axis to cut the slot length. 5. For slots wider than the end mill, take multiple passes offset by 50-75% of the cutter diameter. 6. Finishing pass: climb mill one side, then conventional mill the other side for consistent width.

Pocket Milling

A pocket is a closed cavity with a flat bottom. Strategy:

  1. Plunge the center-cutting end mill at the pocket center (or pre-drill a starting hole).
  2. Spiral outward: Feed in a rectangular or circular spiral pattern, removing material in layers.
  3. Depth increments: Take DOC passes equal to 0.5-1× cutter diameter. Repeat the spiral pattern at each depth level.
  4. Wall finishing: After roughing, make a final pass around the pocket perimeter with a light radial DOC (0.010-0.020") for smooth walls.
  5. Corner radii: The pocket corners will have a radius equal to the end mill radius. Specify corners accordingly.

Profile Milling

Profile milling follows the outside contour of a workpiece: 1. Cut the profile in multiple depth passes. 2. Leave 0.010-0.020" stock for a finishing pass. 3. Finishing: light radial DOC with increased speed and reduced feed for best surface finish. 4. Use climb milling for the finishing pass if the machine has minimal backlash.

Key Talking Points

  • Edge finding is a precision skill—practice until the "kick" is reliable
  • Two-flute end mills are preferred for slots (better chip evacuation)
  • Four-flute end mills provide better surface finish on shoulder and profile cuts
  • Never plunge a non-center-cutting end mill—it will break

Learning Objectives (Concept Check)

  • Can students perform edge finding within 0.001" accuracy?
  • Can students select the correct end mill type for each operation?
  • Do students understand the spiral-outward pocket strategy?

Last Updated: 2026-03-19