5-Axis vs. 3-Axis CNC Machining: Why 3-Axis Cost Less on a 30-Part Robotics Component

A 30-piece robotics structural component initially looked like a clear candidate for 3+2 machining. It had localized curved features and required machining from several directions, so reducing manual setups appeared to be the most stable approach.

During programming, we estimated approximately five hours per part. On the shop floor, the actual production time reached approximately eight hours per part, bringing the 3+2 machining cost to about $340 per part.

We later learned that the customer’s previous supplier had produced the same part on a 3-axis machine using dedicated fixtures. Their reported price was approximately $190 per part.

This does not mean that 3-axis machining is always cheaper or that 5-axis machining is unnecessary. It shows that the machine with more axes is not automatically the best process for every part. Geometry, feature relationships, quantity, workholding, and realistic cycle time all matter.

Confidentiality note: Certain geometry, material, tolerance, and project details have been generalized or omitted because this customer project is protected by a nondisclosure agreement. Customer drawings and part images are not included for the same reason.

Why We Initially Chose 3+2 Machining

The part had several localized curved features, but it was not a complete freeform component. It also required machining from more than one direction.

Our initial process choice was 3+2 positional machining.

In 3+2 machining, the rotary axes position the workpiece at a fixed angle. The machine then cuts with the three linear axes while the rotary axes remain locked. This differs from simultaneous 5-axis machining, in which the tool orientation changes continuously during cutting.

For this part, 3+2 machining appeared to offer three advantages:

• Fewer manual setups
• Easier access to features on different faces
• Better consistency between machining operations

Based on the programmed toolpaths and planned cutting parameters, the estimated time was approximately five hours per part.

Why the Five-Hour Estimate Became Eight Hours

The five-hour figure was a programming-stage estimate, not a measured production cycle.

During actual machining, several shop-floor factors increased the time:

• Cutting parameters required adjustment after the program reached the machine.
• Workholding, setup, and part positioning took longer than the theoretical plan suggested.
• Programmed feeds and cutting speeds could not be maintained throughout every operation under real machining conditions.

Once these factors were included, the actual production time reached approximately eight hours per part.

At the machine-hour rate used for this job—approximately $42.50 per hour—the 3+2 process cost was about $340 per part.

The lesson was not that programming estimates are useless. They are essential planning tools. However, an estimated cycle time for a new process should not be treated as a validated production time until the setup, cutting parameters, and achievable machine speeds have been confirmed on the shop floor.

What the Previous Supplier Did Differently

The customer’s previous supplier used a more traditional process:

• 3-axis CNC machining
• Dedicated fixtures
• Multiple repositioning operations

At first, this appeared less efficient because it required more setups. For this particular part, however, it was the more economical route.

The reason was the geometry:

• The curved features were localized rather than continuous freeform surfaces.
• The required features could be reached from fixed orientations.
• The relationships between features did not require every surface to be machined in one setup.
• A 30-piece order allowed the fixture cost to be distributed across the batch.

The available project figures were:

Because the two routes were run by different suppliers and we did not have the previous supplier’s detailed cost breakdown, this should not be treated as a controlled machine-rate comparison. It is still a useful real-world result: for this geometry and quantity, the fixture-based 3-axis process met the project requirements at a substantially lower reported price.

What We Missed in the Initial Process Review

Our initial review placed too much weight on reducing setups and not enough on the economics of dedicated fixtures.

The part looked complex because it contained curved features. However, the complexity was local, not continuous across the entire component. That distinction mattered more than the number of directions from which the part had to be machined.

We also relied too heavily on the theoretical cycle time. The five-hour estimate reflected the programmed toolpaths, but the final cost depended on the speed the process could achieve under actual cutting, setup, and workholding conditions.

The correct comparison was not simply:

3-axis machining versus a more advanced 5-axis machine.

It was:

A fixture-based 3-axis production process versus a 3+2 process with a higher machine-hour cost and a longer actual cycle time.

What This Changed in Our Process Planning

This experience changed the questions we use when reviewing a part for 3-axis, 3+2, or simultaneous 5-axis machining:

1. Does the tool orientation need to change continuously during cutting?
2. Can the curved features be reached from fixed machining directions?
3. Do features on different faces have strict positional relationships?
4. Is the quantity high enough to justify dedicated fixtures?
5. Does the cycle-time estimate reflect achievable cutting parameters and real setup conditions?
6. How should one-time programming and fixture costs be distributed across the order?

For low-volume, cost-sensitive parts, these questions are more useful than automatically selecting the machine with the most axes.

When Is 5-Axis Machining Still the Better Choice?

This case is not an argument against 5-axis machining. It is an argument for selecting the process around the part.

High precision alone does not automatically require a 5-axis machine. A well-planned 3-axis process can also produce tight-tolerance parts. The deciding factors are usually geometry, tool access, datum relationships, setup risk, quantity, and total manufacturing cost.

Questions to Ask a 5-Axis CNC Machining Supplier

When a supplier recommends 5-axis machining, buyers should ask more than, “Do you have a 5-axis machine?”

More useful questions include:

• Why does this part require 5-axis machining?
• Is the proposed process 3+2 positional machining or simultaneous 5-axis machining?
• Which features benefit from fewer setups?
• How was the cycle time estimated?
• Could a fixture-based 3-axis process lower the total cost at this quantity?
• Are programming, fixtures, and inspection included in the quoted price?

A capable machining supplier should be able to explain why a process was selected—not simply recommend the most advanced equipment available.

Final Takeaway

For this 30-piece robotics project, 3+2 machining was technically capable of producing the part. It was not, however, the most economical process.

The previous 3-axis route worked because the curved features were limited, the critical relationships did not require a single setup, and the fixture cost could be distributed across the batch.

The most advanced machine is not automatically the best manufacturing solution. The right process is the one that meets the drawing requirements with the best balance of quality, stability, lead time, and total cost.

If you have a prototype or low-volume order and are unsure whether it belongs on a 3-axis, 3+2, or simultaneous 5-axis machine, send us your CAD file for an engineering review. We will evaluate the geometry, tolerance relationships, quantity, and cost target before recommending a process. You can also learn more about our 5-axis CNC machining services.