2D Contour

Contour operations are used to rough and finish outside part walls as shown in Figure 7.9. Use Cutter Diameter Compensation (CDC) on high tolerance features so the tool path can be adjusted at the machine if needed to account for tool wear and deflection.

Figure 7.9: 2D Contour Tool Path

Rules for Contouring

• Only use CDC when needed. If using new tools and conservative machining parameters, features will likely be within .005 inches of the programmed path without adjustment.

• Start the tool path off the part to allow CDC to be fully in effect for the entire operation. The combined line-arc lead-in/out moves shown in Figure 7.9 work for most contours. The line is for activating/deactivating compensation, and the arcs blend the path into the part wall smoothly.

• Set a rapid height value to clear all clamps or other obstacles between cuts.

• Rough the walls and leave a constant thickness of material for the finish operation. This ensures even cutting pressure on the finish pass and thus a more accurate part.

• Extend the cut depth of full walls slightly below the bottom of the wall, but be careful not to cut into the machine table or vise hard jaws! This way, when the part if flipped over to face the other side, no flashing will be left on the bottom of the walls.

• Mill tools cut well in the XY direction, but not as well when plunging in Z. When possible, plunge the tool away from the part to avoid Z-moves into the stock material.

• When taking multiple depths of cut, make the last pass at full depth to remove any marks left by previous depth cuts.

• For tall walls, consider taking one additional finish pass. This so-called "spring pass" follows the same path twice to ensure the walls are perfectly straight and not slightly tapered due to cutting pressure which causes the tool to bend.