Rotary axis configuration
The post defines the 4th axis: which linear axis it rotates around (A about X on most VMCs, B about Y on HMCs), direction, limits and whether it can rotate continuously.
var aAxis = createAxis({
coordinate: 0, // A axis
table: true,
axis: [1, 0, 0], // rotates about X
cyclic: true, // continuous rotation
preference: 0
});
machineConfiguration = new MachineConfiguration(aAxis);
setMachineConfiguration(machineConfiguration);Exact syntax depends on the post version; newer Autodesk library posts define axes in a dedicated machine configuration function.
Indexing vs continuous 4-axis
| Mode | Post behaviour |
|---|---|
| Indexed (positional) | Rotate, clamp, cut in 3-axis, unclamp |
| Continuous (wrapping, rotary finishing) | Unclamped A with simultaneous XYZA motion |
Clamping and brake codes
M11 (unclamp A)
G00 A90.
M10 (clamp A)
(... 3-axis cutting on this face ...)Clamp codes differ between machines and rotary table brands, so they must come from the machine documentation.
Feedrate with rotary motion
When the A axis moves together with linear axes, the controller's feed interpretation matters. Depending on the machine, the post outputs inverse time feed (G93) or calculates an equivalent degrees-per-minute feed so the tool moves at the intended speed across the part surface.
Direction and wrap-around
For continuous A axes, the post chooses the shortest rotation and handles values beyond 360°. Some controllers use rollover settings; others need explicit direction handling. This is one of the most common 4-axis issues in generic posts.
Most 4-axis problems are configuration problems: the post simply doesn't know how the table is mounted.
Fusion 4-axis posts
See our Fusion 360 customisation service and 4-axis milling post development.