GlossaryKind of term: Manufacturing term3+2 machining
What is 3+2 machining?
In 3+2 machining the two rotary axes of a 5-axis machine fix the orientation of tool to part, after which the machine mills with its three linear axes.
In 3+2, also called positional or indexed 5-axis milling, a 5-axis machine uses its two rotary axes only to position. The table or head tilts and rotates to a fixed orientation of tool to part, the rotary axes are locked, and the machine cuts with X, Y and Z in a tilted work plane. Then it moves on to the next orientation. The rotary axes stand still during the cut. This can bring more sides and angled faces within reach in one setup.
What does 3+2 machining depend on?
Which sides you reach in one setup depends on the kinematics (trunnion table, swivel head or a combination), the tilt ranges, the workholding, the tool length and collisions with holder and spindle head. The face the part is clamped on stays out of reach; that needs a second setup, a clamping margin or different workholding. Because the part is not released, the reclamping error between orientations disappears, but the relative position then depends on the accuracy and kinematic calibration of the rotary axes. Tilting often lets a shorter tool reach a deep wall, with less chatter. The postprocessor must output the tilted work plane correctly for that machine's kinematics and control.
How does 3+2 machining work in practice?
3+2 is a trade between setups and hourly rate. A 5-axis machine usually carries a higher rate than a 3-axis machine, and a part that can be made from one side gains little. On a one-off or small batch with features on several sides, saving setups can weigh more. Features with a tight location or orientation tolerance between them are often easier to hold in one setup. Which route is cheaper depends on quantity, hourly rates, programming time and the workholding already on the shelf.
What is 3+2 machining often confused with?
3+2 is not simultaneous 5-axis milling: in 3+2 the rotary axes stand still during the cut, in simultaneous work they move with it. Nor is it a fourth axis: a rotary table on a 3-axis machine turns about one axis and brings the sides around it square to the tool, but not faces angled in two directions.
How do you see 3+2 machining in Blake?
In Blake you enter the setups per route yourself, so 3+2 on a 5-axis machine and reclamping on a 3-axis machine each work with their own setup count. Your machine park records each machine's axes, envelope and hourly rate; a first check per machine shows which limit decides. More on milling.
Frequently asked questions
When is 3+2 better than reclamping on a 3-axis machine?
When the setups you save outweigh the higher hourly rate and the programming time. That is often the case on one-offs and small batches with features on several sides, and with tight tolerances between features on different sides.
Does 3+2 reach every side in one setup?
Usually not. The face the part is clamped on stays out of reach, and tilt range, holder and workholding limit the orientations. That needs a second setup, a clamping margin you machine off later, or different workholding.
Do you need advanced CAM for 3+2?
Less than for simultaneous work. You program each orientation as 3-axis work in a tilted plane. You do need a postprocessor that outputs your machine's rotary axes and work plane correctly, and a simulation helps find collisions in the tilted orientation.