3-Axis, 5-Axis or Mill-Turn: Which Machine Does Your Part Need?

Two shops can quote the same drawing on different machines, and the machine they choose shapes the price. A part that needs five separate clampings on a 3-axis mill might come off a 5-axis machine in one or two. A turned part with cross holes might need a lathe and a mill, or a single mill-turn centre. This guide matches common part shapes to the machining routes that suit them, explains why set-ups drive cost, and lists what to send so suppliers can quote the right route.

Start with the part, not the machine

Ask three questions. Is the part mostly round or mostly prismatic (block-shaped)? How many faces carry features? Are there angled holes, undercuts or curved surfaces that a straight-down cutter cannot reach? The answers point to the right route.

3-axis milling: prismatic parts machined from one direction at a time

A 3-axis mill moves the cutter in X, Y and Z, always approaching from above. It suits plates, brackets, covers, manifolds and housings whose features sit on one or two faces. Each extra face usually means turning the part over and clamping it again. For simple parts that is no problem, and 3-axis machine time is often the lowest-cost time in the shop.

3+2 machining: several faces in one clamping

On a 3+2 (or positional five-axis) machine, the two rotary axes tilt the part or the head to a fixed angle and lock, and the cut itself is ordinary 3-axis work. The machine then indexes to the next angle. This reaches five sides of a block and angled holes without re-clamping, which suits housings, valve bodies and parts with features on several faces. Many shops use 3+2 for most of their five-axis work.

Simultaneous 5-axis: curved surfaces and hard-to-reach features

In simultaneous 5-axis machining, all five axes move during the cut, so the tool stays at the best angle to a curved surface. It suits impellers, blades, ports, moulds and freeform shapes, and lets the shop use shorter, stiffer tools on deep features. Programming takes longer and the machine rate is usually higher, so it pays off when the geometry needs it.

Turning: round parts

A lathe spins the material and a fixed tool cuts it, which makes it the natural route for shafts, pins, bushes, spacers and threaded parts. Diameters, faces, grooves and threads on a common axis are all lathe work.

Mill-turn: round parts with milled features

A mill-turn centre is a lathe with driven (live) tools, and often a Y axis and a second spindle. It can turn a part, then drill cross holes, mill flats, slots and hexes, and finish the back face without the part leaving the machine. For a turned part with milled features, that removes a second machine and a second set-up.

Swiss-type: long, slender, small-diameter parts

A Swiss-type (sliding head) lathe feeds bar stock through a guide bush and moves it past the tools, so the cut is always close to where the material is supported. That keeps slender parts from deflecting, which suits pins, screws, connector contacts and medical and electronic components. Mainstream machines typically take bar up to around 32 mm, with some larger. Swiss-type lathes are usually bar-fed, which suits batch and repeat production.

Quick reference

Why set-ups drive cost

Every set-up means a fixture to make or select, a datum to pick up again, a first part to prove and inspect, and time when the machine is not cutting. Each re-clamp also adds a small chance that features made in different set-ups will not line up as well as features made in one. Fewer set-ups usually means less handling and better positional accuracy between features.

That does not mean the most capable machine is always the cheapest. A 5-axis or mill-turn machine usually costs more per hour, so a simple bracket can be cheaper on a 3-axis mill even with two set-ups. The best route depends on the geometry, the tolerances and the quantity. At one or two parts, set-up time dominates. At hundreds, cycle time matters more, and a route that saves seconds per part can be worth extra fixture work. Our guide to what affects the cost of CNC machining covers the other price drivers.

What to send for a quote

• A 3D model (STEP is widely accepted) and a 2D drawing with tolerances, revision shown
• Material, grade and any certificate you need
• Quantity now, and expected repeat or annual quantity
• The features that are critical to function, marked on the drawing
• Surface finish, coatings and inspection needed
• The date you need the parts by

The repeat quantity matters because a shop may plan a different route for 10 parts than for 1,000.

Questions to ask each supplier

1. Which machine would you use, and how many operations or set-ups does that take?
2. Would a small design change, such as moving a hole or opening up a radius, remove a set-up?
3. How does the price change at 1, 10 and 100 parts?
4. Does the price include fixtures and a first article inspection report?
5. Is the whole part made in-house, or is any operation sent out?

Quick-reference checklist

• Decide whether the part is round or prismatic, and count the faces with features
• Mark the features that must line up with each other
• Send a model and a drawing to every supplier
• Give current and repeat quantities
• Ask each supplier for its route and number of set-ups
• Compare quotes on the same drawing, quantities and scope

Find CNC machining companies on CNC Directory

CNC Directory lists 300+ UK machining companies. Browse CNC milling, CNC turning, 5-axis and multi-axis machining and Swiss machining, and use the Machine Capabilities filter to narrow by 3-axis, 4-axis, 5-axis, live tooling, Swiss-type and multi-spindle. Our guide to choosing a UK CNC machining supplier covers certifications and inspection. Save the companies that fit to your shortlist and send one enquiry to the whole shortlist at once.