Why the internal corners in CNC part design are the core challenge of 5-axis machining
In the precision CNC part custom processing, the internal corner (Undercut) or deep cavity structure often leads to the tool being unable to fully contact the geometric surface, residual material causing appearance defects and functional failure. For products that require high gloss, no scratches and high mass production consistency, this type of design flaw not only increases rework costs, but may also cause stress concentration and assembly interference.
Traditional 3-axis milling is limited by the fixed posture of the tool shaft perpendicular to the workpiece surface, when machining the internal R corner, deep cavity or inclined side wall, it is easy to produce "over-cutting" or "under-cutting". In this case, 5-axis simultaneous machining by coordinated control of X, Y, Z linear axes and A, B rotary axes, the tool is able to cut into the dead end at an optimized posture, completely solving the machinability of the internal area. This article is based on engineering practice, analysis of how to avoid internal corner risks through design optimization and 5-axis path strategy.
The engineering impact of internal corners on CNC machinability
Tool radius and dead end depth geometric limit
In the design stage, the engineer must first evaluate the tool ability. Suppose a ball-nose tool of diameter D is used to machine the internal corner R, if the internal depth H is less than the tool ball radius Rt, and the internal angle θ is limited, the tool ball and the part surface will produce interference. Based on the geometric relationship, the minimum machinable internal radius usually needs to meet R_min ≥ D/2 + safety margin. If the internal R corner in the design drawing is less than this value, and the depth is deep, the 3-axis tool cannot be ground, and it must rely on the 5-axis lateral feed or smaller diameter tool (which brings strength and vibration problems).
Stress concentration and appearance quality dual risks
Internal dead corners are not only machining difficulties, but also structural weaknesses. Sharp internal corner (R
