Engineering Guides
More axes mean fewer setups and access to more angles, but also a higher hourly rate. This guide explains what each machine type does and when 5-axis machining actually lowers the cost of a part.
3-axis CNC milling moves the tool along X, Y and Z and suits flat or prismatic parts machined from one or two sides. 4-axis adds a rotary axis, usually around X, so features around a cylinder or on four sides can be cut in one setup. 5-axis adds two rotary axes, so the tool can reach almost any face and angle; it pays off when a part would otherwise need many setups, when features on different faces must be accurately positioned relative to each other, or when the geometry is a free-form or undercut shape that a 3-axis machine cannot reach.
A CNC milling machine moves a rotating cutter relative to a workpiece. Each independently controlled motion is an axis:
A 4-axis machine has X, Y, Z plus one rotary axis (usually A). A 5-axis machine has X, Y, Z plus two rotary axes, commonly A and C on a trunnion table, or B and C, or a tilting head.
On a 3-axis mill the tool always points straight down the Z axis. Any face the tool needs to reach must face upward, so the part is unclamped, flipped and re-clamped for each side. Each new setup is called an operation or "op."
3-axis is the right choice for:
It is the cheapest option per machine hour, setup and programming are straightforward, and most machined parts in the world are still made on 3-axis machines.
The fourth axis is a rotary table or indexer, usually mounted so the part rotates around the X axis. Two modes exist:
4-axis suits:
With two rotary axes, the tool can be oriented at almost any angle to the part. There are two main ways to use it:
Also called positional 5-axis, 3+2 machining tilts and rotates the part to a fixed orientation, then machines it with three linear axes. It is used for parts with features on many faces or at compound angles. The benefit is fewer setups and shorter, more rigid tools, because the tool can approach the feature directly instead of reaching over the part.
All five axes move together during the cut. This is needed for free-form surfaces such as impellers, turbine blades, propellers, ergonomic housings, orthopedic shapes and complex mold cores. The tool stays at the optimal angle to the surface, so the side of a cutter can be used instead of the tip, giving better surface finish and shorter cycle times.
| Factor | 3-axis | 4-axis | 5-axis |
|---|---|---|---|
| Axes | X, Y, Z | X, Y, Z + one rotary | X, Y, Z + two rotary |
| Typical parts | Plates, brackets, covers, pockets | Shafts with cross features, multi-side blocks, cams | Multi-face housings, compound angles, impellers, free-form surfaces |
| Setups for a 6-sided part | Often 4–6 | Often 2–3 | Often 1–2 |
| Feature-to-feature accuracy across faces | Limited by re-clamping | Better around the rotary axis | Best, when cut in one setup |
| Undercuts / compound angles | Special tools only | Limited | Yes |
| Programming effort | Low | Moderate | Higher (CAM, collision checking, simulation) |
| Machine hourly rate | Lowest | Moderate | Highest |
| Best for | Simple geometry at any volume | Rotational multi-side features | Complex geometry, tight cross-face tolerances |
5-axis costs more per machine hour, so it pays off only when it removes enough other cost or makes a part possible. It usually makes economic sense when:
You do not need to specify the machine on the drawing — the supplier chooses the process. But design decisions influence which machine is needed:
Our DFM rules for CNC machining cover more of these design choices, and the tolerance guide explains how setups affect positional tolerances.
For round parts, the comparison is not only between milling machines. Turn-mill centers combine turning with live tooling and a C axis (and sometimes a Y or B axis), so a shaft or knob can be turned, cross-drilled, flatted and milled in one setup. Swiss-type style lathes are efficient for small, slender turned parts. If your part is mostly round, ask whether turning is the better route — see our guide to machining custom metal knobs for an example.
Axisform runs 3-, 4- and 5-axis CNC milling alongside CNC turning, turn-mill, wire EDM and broaching. For each RFQ, the machining route is chosen by geometry, tolerance and quantity rather than by default, and the quote reflects that route. You can see examples on our projects page or send a STEP file and drawing through contact.
A 5-axis machine is not inherently more accurate on a single feature, but it can cut features on several faces in one setup. That avoids re-clamping error, so positional accuracy between faces is usually better on complex parts.
The hourly rate is higher, but the part price is not always higher. When a part would need many setups or special fixtures on a 3-axis machine, 5-axis can be equal or cheaper overall. For simple flat parts, 3-axis remains cheaper.
In 3+2 machining the rotary axes position the part at a fixed angle, then the machine cuts with three linear axes. In full or simultaneous 5-axis, all five axes move together during the cut, which is required for free-form surfaces like impellers and blades.
No. Specify geometry, tolerances and datums, and let the supplier choose the process. Mention it only if a specific surface finish or tool path requirement makes a particular method necessary.
Send your drawing and an engineer will reply with DFM notes and a quote within 24 hours.
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