Guides / Process

Simultaneous 5-Axis or 3+2 for Your Prototype: How to Tell

September 29, 2026

Most shops that list “5-axis” on their capability page can position a part at a compound angle. Fewer can cut with all five axes moving at once. For many prototypes that difference does not matter. For some it decides whether the part can be made at all without hand blending. This guide explains the two modes, which features need which and how to confirm what a shop actually runs before you send a drawing. The machine mode is the second choice after the method; our guide to 5-axis CNC prototyping covers both.

What 3+2 means

In 3+2 machining (also called indexed or positional 5-axis) the two rotary axes turn the part or the head to a fixed angle and lock. The three linear axes, X, Y and Z, then cut as they would on a 3-axis machine. When that face is done, the rotaries move to the next angle, lock again and the next set of features is cut.

The result is a 3-axis toolpath on a tilted plane. The machine reaches five or more faces in one clamping, uses shorter tools because it can tilt the part toward the spindle and holds position between faces because the part never leaves the fixture. Most of the setup savings people associate with 5-axis come from this mode.

What simultaneous 5-axis means

In simultaneous (or continuous) 5-axis all five axes move together during the cut. The tool changes its angle to the surface continuously as it travels. The control has to coordinate rotary and linear motion so the tool tip stays on the programmed path, a function usually called tool center point control (TCPC, RTCP or TCPM depending on the builder).

This is what you need when a surface curves in two directions and the tool must stay normal to it, or tilted at a set lead angle, along the whole path. It is also what lets a tool reach into a twisted channel between two blades where no fixed angle gives clear access. For general background, see the overview of multiaxis machining.

Why “5-axis” on a shop page often means indexing

A trunnion machine that indexes well is a very productive tool for prismatic parts, and many shops use it that way almost all of the time. Running simultaneous work needs more than the machine:

• a control option for tool center point management, which is not always purchased
• CAM software licensed for multi-axis toolpaths, which costs more than a 3-axis or 3+2 seat
• a verified post processor for that exact machine kinematics
• full machine simulation, so the programmer can check head, holder and trunnion against the part and fixture
• programmers who do this work often enough to be quick at it

A shop can have the machine and none of the rest. That shop is honest when it says “5-axis” and still cannot cut an impeller. The question is not whether the machine has five axes but which of them move during the cut.

Feature by feature: which mode does the part need

Feature	3+2 indexed	Simultaneous 5-axis	Notes
Holes and pockets on several angled faces	Yes	Not needed	Classic 3+2 part
Compound-angle bores	Yes	Not needed	One index per bore axis
Flat faces at odd angles	Yes	Not needed	Face mill or end mill on a tilted plane
Variable-angle chamfers along a curved edge	Poor	Yes	3+2 leaves steps or needs hand work
Freeform surfaces with a smooth finish requirement	Possible with small step-over	Better	3+2 uses ball end mills and many passes
Impeller and blisk blades, flow channels	No	Yes	Tool must follow the twist
Undercuts reachable only along a changing angle	No	Yes	Access changes along the path
Swarf-cut ruled walls (tapered or twisted sidewalls)	No	Yes	Side of the tool cuts the whole wall
Blended ports and internal curved passages	Limited	Yes	Common on manifolds and housings
Deep cavities where a short tool must tilt as it goes	Limited	Yes	Avoids long tool deflection

If every row that applies to your part says “Yes” in the 3+2 column, you do not need simultaneous capability and you should not pay for it. If one feature needs it, the whole part goes to a shop that runs it.

What the choice does to CAM time, setups, finish and cost

CAM time

A 3+2 program is a set of 3-axis programs on rotated planes. A capable programmer can typically build one for a moderately complex prototype in a few hours. A simultaneous program needs tool axis control strategies, collision checks along the whole path and careful review of the posted code. For an impeller or a blended port, one to three days of programming is typical. On a one-off prototype that programming time is often the largest line on the quote.

Setups

Both modes cut most faces in one clamping. Compared with 3-axis the gain is large either way: a part that needs 4 to 6 setups on a 3-axis mill can often be cut in one or two fixturings on a 5-axis machine. Fewer setups means fewer chances to lose position between faces, which matters most for features that must line up across the part.

Surface finish

On a freeform surface cut in 3+2 the tool sits at a fixed angle. The shop usually uses a ball end mill with a small step-over, and the finish shows scallops between passes. Scallop height depends on tool radius and step-over. Getting it small means many passes and long cycle time. Where the surface crosses from one indexed zone to the next, you may see a witness line or step-over mark.

Simultaneous 5-axis can tilt the tool and cut with the side of a larger tool, a barrel cutter or a lead-angled ball, so each pass covers more surface. The result is typically a more uniform finish in less time, with fewer blend marks that someone would otherwise remove by hand.

Cost

For a part that does not need it, simultaneous programming adds cost with no benefit. For a part that does need it, the alternatives usually cost more: extra setups, custom form tools, EDM or hours of hand blending that no one can repeat exactly on the next revision. Match the mode to the feature and the cost follows.

When 3+2 is the better choice, even on a simultaneous machine

Shops that run simultaneous work still cut most features in 3+2. Indexed toolpaths are easier to program, easier to prove out and more rigid, because the rotary axes are clamped during the cut. Heavy roughing, drilling, tapping and boring are almost always indexed. A good program for a complex part often combines both: 3+2 roughing and hole making, then simultaneous finishing on the surfaces that need it.

So the right question for a prototype is not “3+2 or simultaneous” for the whole part. It is which features need continuous motion, and whether the shop can cut those well.

Example parts and the mode they usually need

• Impellers and blisks. Twisted blades and narrow channels. Simultaneous 5-axis in nearly every case.
• Optical mounts. Precision bores and datum faces at compound angles. Usually 3+2, with the value in holding position across faces in one clamping.
• Surgical tooling. A mix of both. Jaw profiles and ergonomic handles may need continuous toolpaths. Hinge bores and pin holes are indexed work.
• Drone gimbals. Thin arms, angled bosses and weight-relief pockets. Mostly 3+2. Organic, topology-optimized shapes push toward simultaneous.
• Manifolds. Cross-drilled ports are 3+2. Blended internal passages and smooth port transitions are simultaneous.
• Housings with sculpted exteriors. Pockets and bores are indexed. Curved outer skins with a cosmetic finish are simultaneous.

For a wider view of when 5-axis makes sense at all compared with 3-axis or additive, see 5-axis prototyping vs 3-axis and 3D printing.

How to check whether a shop really runs simultaneous

Ask direct questions. A shop that does this work answers them quickly and specifically.

1. Machine model and configuration. Trunnion table, swivel head or head-head. The configuration sets the work envelope and which angles are reachable.
2. Control and options. Which control, and whether tool center point control is active on that machine.
3. CAM software. Which package, and whether the seat includes multi-axis toolpaths, not only 3+2 positioning.
4. Post processor. Whether the post is verified for that machine and who maintains it.
5. Collision simulation. Whether the programmer runs full machine simulation with holder, head and fixture, or only toolpath verification.
6. Sample parts. Photos of parts cut with continuous toolpaths: impellers, blended surfaces, swarf-cut walls. A shop that only indexes will show prismatic parts.
7. Recent volume. How often they program simultaneous jobs. A shop that does one a year will be slower and more expensive than one that does several a week.

You can also send the model and ask the shop to say which features it plans to cut in each mode. A clear answer tells you it looked at the part. A vague “no problem” tells you little.

Common mistakes on prototype RFQs

• Asking for “5-axis” without saying why. The shop may quote indexed work for a part whose blades need continuous toolpaths, then find out during programming.
• Tight profile tolerance on every surface. A profile tolerance of 0.02 mm across a whole freeform skin drives step-over, cycle time and CMM time. Apply it where the surface does work and use a looser profile elsewhere.
• Leaving finish unspecified. Without a Ra value, one shop quotes a fine finishing pass and another quotes a rough scallop. The quotes are not comparable.
• Changing shops between revisions. A simultaneous program is expensive to build. The shop that wrote it can edit it for Rev B for much less than a new shop can write it again.

Checklist before you send the RFQ

• Mark the features that need a continuous toolpath, or ask the shop to identify them.
• State the finish you need on freeform surfaces as a Ra value, and where cosmetic appearance matters.
• Say whether hand blending is acceptable. If it is not, write that on the drawing.
• Send a clean STEP file plus a PDF drawing with critical tolerances and datums. The materials table lists typical tolerances by material.
• Give quantity per revision and whether a Rev B is likely, so the shop can plan to reuse the program.
• Ask for a note in the quote on which mode the shop plans to use for each critical feature.

See also: the reference page on simultaneous 5-axis machining, with CAM hours and cost per part by part type.

Send the drawing

If you are not sure which mode your part needs, that is a normal starting point. Send the drawing with one RFQ and we match it with up to three shops that run 5-axis, including simultaneous work where the geometry calls for it. Shops quote you directly, the service is free for buyers and an NDA is available on request. You get a reply within 24 business hours.

Frequently asked questions

Keep reading

• Revising a 5-Axis Prototype Between Iterations Without Restarting
• Aerospace Bracket Prototypes: 5-Axis Parts Before Qualification