When designing triangular inside corners, one inside corner must include a radius
All CNC milling cutters are cylinder-shaped and create a radius when cutting into corners.
Avoid angles of inclination sharper than a right angle, where possible. When working with sharp angles of inclination, there will always be an area at the bottom of two angles that is unreachable for the milling cutter. This is because most common cutting tools have a 90-degree work area. Add radii to the bottom of sharp angles of inclination at least 1/5 of the depth of the hollow (the larger the better).