The use of three-axis toolpaths [2, 3, 5] is sufficient as long as the part is not too deep with respect to the cutter diameter. If the part is deep and has narrow cavities, using pure three-axis toolpaths is not sufficient for the complete finishing process of the part.

This is especially true if milling hard material with long cutters results. In this case bad surface finish and long machining times may ensue.
To utilize a shorter tool the spindle is tilted with an inclined view such that a specific region of the part can be machined with the shorter tool. The process of setting a constant angle to the spindle is generally known as 3+2-axis machining. Complex parts may require dozens of inclined views to fully cover the whole part. The resulting toolpaths must overlap—leading to increased machining time.

Additionally it can be difficult to perfectly blend all of the inclined views, resulting in increased hand polishing. At the same time the number of lead-in and out movements increases dramatically, which often results in surface quality problems and more tool movements.

Finally, programming in this way can be quite interactive and time consuming for the user and often the sum of all views does not cover the whole geometry.
In order to overcome the drawbacks of 3+2-axis machining, one may choose to implement simultaneous five-axis machining, using functions designed specifically for the moldmaking industry. Simultaneous five-axis machining incorporates the three linear axes and two rotational axes at the same time. It solves all of the problems of three-axis and 3+2-axis machining. The cutter can be very short, no overlapping views need to be generated, the probability of missing an area is much smaller and the machining can be performed continuously without additional lead-ins and lead-outs