In three-plus-two, the two rotary axes move the part or head to an angle and then lock, and cutting is done with the three linear axes. In simultaneous five-axis, all five axes move during the cut. Most general engineering five-axis work is three-plus-two, and it delivers the setup reduction that justifies the machine. Simultaneous machining is needed for impellers, blades and complex free-form surfaces.

Fewer setups. A prismatic part with features on several faces can be completed in one operation rather than being unclamped, repositioned and re-datumed several times. That saves handling time and, more importantly, removes the positional error that accumulates between setups, which is often what determines whether a tolerance between features on different faces can be held at all.

Because tilting the head or the part lets a tool approach a deep or awkward feature from an angle instead of reaching past an obstruction. A shorter tool deflects less, allows higher feeds and speeds, chatters less and leaves a better surface. That gain in rigidity is a genuine and frequently underrated benefit of five-axis machining, separate from the ability to reach the feature at all.

Trunnion or table-table machines rotate the part on a tilting cradle, which suits smaller parts and gives good rigidity. Head-head machines rotate the spindle, which suits large or heavy parts that cannot be tilted. Table-head splits rotation between the two. The choice follows part size and weight, since anything the table must tilt has to be within its capacity and swing envelope.

CAM software capable of five-axis toolpaths, a correctly configured post-processor for the specific machine and control, workholding that presents the part clear of the rotating envelope, tool libraries with accurate geometry, and kinematic calibration so the control knows precisely where the rotary centres are. These are frequently underestimated, and they determine whether the machine delivers what it was bought for.

Yes, materially. With the head or table tilting, the tool, holder, spindle nose, fixture and enclosure can all interfere in ways that are not obvious from a three-axis mindset. Full machine simulation with accurate models of the fixture, holder and machine envelope is standard practice rather than an optional check, and most five-axis crashes trace back to a simulation that did not include something real.

Often yes, but for setup reduction rather than for complex surfaces. If parts routinely need three or four setups, a five-axis machine consolidates them and pays back through labour and improved accuracy between features. If work is simple and prismatic, or if the shop cannot support the programming and calibration effort, a fourth axis on a vertical machine may capture most of the benefit for far less.