Why 3+2 Is Often Faster Than 5-Axis
You’ve programmed the part in continuous 5-axis. CAM predicts 20% faster. You send it to the machine. It runs slower than 3+2 would have.
This isn’t a one-off. It’s the gap between CAM predictions and machine reality.
The Hidden Slowdown
Continuous 5-axis demands constant coordination of all five axes. When programmed feedrates hit kinematic limits during tool reorientation, the controller decelerates to maintain accuracy. CAM doesn’t see these slowdowns.
Siemens knows that you get “frequently longer machining times due to compensatory movements of the kinematics” and FANUC says that “because of the constant acceleration and deceleration of the axis and the fact that the abrupt changes cause machine shock and vibration, feedrates are limited.”
However, when machining in 3+2, the rotary axes are locked. Only three linear axes move during material removal. No rotary kinematics forcing deceleration. More consistent feedrates throughout.
Quality Matters More
Beyond cycle time, there’s a bigger problem. Feedrate fluctuations in 5-axis leave witness marks and surface artefacts.
On thin-walled aerospace parts, any feedrate variation shows as a finish defect. For medical devices, it impacts final quality. For precision components, it means rejection.
Siemens is explicit: “Even the smallest jumps in deceleration and acceleration can result in surface defects (e.g. chatter marks).” FANUC describes it exactly: “The modern CNC will faithfully reproduce those small segments generating witness lines on the part.”
With 3+2, you eliminate feedrate variations from rotary axis dynamics. Locked tool axis means more consistent chip load, improved surface finish and longer tool life.
When 5-Axis Works
This isn’t anti-5-axis. It’s about choosing correctly. True simultaneous 5-axis excels for sculptured surfaces requiring continuous tool tilt, deep cavities needing collision avoidance during cutting, and parts demanding continuous rotation for accessibility.
But for many components (especially those decomposable into distinct orientations), 3+2 delivers better results. Both Siemens and FANUC recommend: “As much as possible 3-, 3+1- and 3+2-axis roughing/semi-finishing. 5-axis simultaneous milling only for the finishing.”
The Real Cost of Guessing
CAM can’t tell you which approach performs better on your specific machine. Without understanding machine kinematic capabilities and toolpath interaction, you’re programming blind.
On a recent aerospace use case: CAM predicted 40 seconds for a deep-pocket aluminium operation. Actual time? Three minutes. That’s 4.5x error. Not programmer mistake. CAM simply can’t account for machine kinematic limits.
FANUC testing shows the scale of the problem. Their comparison data: setup dropped from 2.5 hours to 30 minutes, cycle time reduced from 80 minutes to 40 minutes, surface finish improved from rough to smooth. Same machine, same part, different approach.
Testing strategies costs real money. Each test consumes machine time, material, programming effort. For aerospace manufacturers, testing five strategies on a one-hour process can cost £1,500 in machine time while producing nothing.
Make Better Decisions
The path forward isn’t avoiding 5-axis. It’s knowing when to use it. Recognising the gap between CAM predictions and machine performance lets you make programming decisions that optimise both cycle time and quality.
The question isn’t whether your machine has 5-axis capability. It’s whether continuous 5-axis is the right strategy for this part, on this machine, with these quality requirements.
Want to learn more about bridging the gap between CAM and machine performance? Join our upcoming webinar and learn more about What Your CAM Software Doesn’t Tell You About 5-Axis Machining.