5-Axis vs 3+2 Machining

Continuous 5-axis and 3+2 indexed machining both use 5-axis machines. The difference is in the motion — and the cost.

What 3+2 actually means

In 3+2 machining (also called positional 5-axis), the rotary axes lock at a fixed angle, then the machine cuts using only X, Y, and Z — standard 3-axis motion. The "+2" means two rotary axes positioned the part, then held it there. The cutting is 3-axis. The indexing is 5-axis.

This is how most "5-axis" work is actually done. A part with features on the top, two sides, and an angled face gets indexed to 4 positions, and each position is machined in 3-axis. The 5-axis machine is used as a highly flexible fixture, not for simultaneous motion.

What continuous 5-axis means

In continuous (simultaneous) 5-axis, all five axes move at the same time during the cut. The tool orientation changes constantly as it follows a sculpted surface or compound curve. The machine interpolates X, Y, Z, A, and B (or C) together in every line of code.

This is required for impellers, turbine blades, propellers, mold surfaces with deep undercuts, and any geometry where the surface normal changes continuously. You can't index to a fixed angle because there's no single angle — the tool must tilt and swivel as it moves.

Cost difference

3+2 programming costs are comparable to 3-axis: $50-150/hour, 1-4 hours for a typical part. The programmer creates standard toolpaths for each indexed position. Standard CAM software (Mastercam, Fusion 360, GibbsCAM) handles this well.

Continuous 5-axis programming costs 2-5x more. The toolpaths are complex, collision avoidance is critical, and simulation time is longer. A skilled 5-axis programmer commands $80-150/hour, and a complex part might take 8-20 hours to program. This cost is amortized over production volume but dominates on first-run parts.

Machine rates are the same — the hourly rate is based on the machine, not the motion type. A shop charging $130/hour for continuous 5-axis charges the same for 3+2 on the same machine. The cost difference is in programming and cycle time.

When continuous 5-axis pays for itself

Sculpted surfaces with changing surface normals — you can't do these any other way. Impellers, turbine blades, airfoils, and complex mold cores require true simultaneous motion.

Tool reach problems where the part geometry forces a long tool into a deep pocket. Continuous 5-axis lets you tilt the tool to use a shorter cutter with better rigidity. The cycle time may be the same, but the surface finish is dramatically better and the tool life is 3-5x longer.

Thin-wall machining where cutting forces need to be controlled. Continuous 5-axis can orient the tool to always cut in the direction of maximum wall support, reducing deflection and enabling thinner walls than 3+2 can achieve.

When 3+2 is the smarter choice

Most of the time. If your part has flat faces, straight walls, holes at compound angles, and pockets — 3+2 handles it with simpler programming, faster prove-out, and lower risk. The majority of aerospace brackets, medical housings, and mold components are 3+2 parts running on 5-axis machines.

The question to ask: does the tool orientation need to change during the cut, or just between features? If it only changes between features, 3+2 is the answer.