Rake Angle
Rake angle is the angle between a cutting tool's rake face and a line perpendicular to the workpiece or feed direction. It governs how chips flow off the tool and how aggressively the edge engages material. Positive rake facilitates easier cutting, negative rake strengthens the edge but increases forces. The selection directly affects chip formation, cutting forces, heat generation, surface finish, and tool life in CNC machining.
In a real CNC shop, rake angle is fixed in the tool geometry and chosen before the program runs. For turning, side rake heavily influences chip flow and cutting force direction, so operators match it to material hardness and finish requirements. In milling, rake angle determines whether the cutter shears cleanly or pushes material, directly impacting spindle load, heat buildup, and the likelihood of built-up edge or poor chip evacuation. On wood-based materials like MDF or particleboard, a favorable rake reduces tear-out and fuzzing, while an unfavorable one worsens edge fracture. The physical tradeoff is key: a higher positive rake lowers cutting forces and helps chips flow, but it weakens the edge, making it unsuitable for interrupted cuts or hard materials. Conversely, a negative rake boosts edge strength at the cost of higher resistance and heat. Machinists adjust rake by swapping inserts or regrinding tools, not during the cut, and they balance these factors to maintain cycle times, tool life, and surface quality.
Does increasing rake angle always improve machining?
No. A larger positive rake lowers cutting force and improves chip flow, but it reduces edge strength, making the tool prone to chipping under heavy or interrupted cuts. Tool selection is a tradeoff between sharpness and durability.
Why do some inserts use negative rake?
Negative rake improves cutting-edge support and resistance to heavy shear loads. This is useful in demanding or interrupted cuts, even though it raises cutting force and heat, because the edge is less likely to fracture.
What is the main process effect of rake angle?
Rake angle primarily controls cutting force, chip flow, heat generation, and surface integrity. It also has secondary effects on tool wear and energy use, making it a critical parameter for process stability and part quality.