Article

When Should You Machine FDM Parts?

When you have a complex geometry that is ideal for FDM, but the part requires critical dimensions and fine features that can’t be achieved as printed, CNC machining after 3D printing will deliver the part you need.

FDM works with engineering-grade thermoplastics that are used for production applications with high requirements. FDM is an ideal choice for production parts because of the unparalleled design freedom possible with the technology while achieving durability and excellent strength-to-weight ratios. The addition of CNC machining to an FDM part manifests in even more accurate parts in lightweight and robust materials.

Additionally, the combination of the two processes can be quicker than most traditional manufacturing methods. Even accounting for printer set up, build, finishing and machining, the additive + machining method is faster than designing and producing a tool for injection molding. It also allows for greater flexibility to make design improvements.

Capabilities of CNC Machining FDM Parts

At Stratasys Direct we’ve seen the marriage of additive and conventional technologies add significant value to FDM parts in the following ways:

• Boring, drilling and reaming features for better accuracy
• Machining an entire part to specific dimensions
• Machining mating features to aid in increased fitment in assembly
• Circular machining for interior bores and exterior profiles
• Face milling for accurate, flat, and smooth surfaces
• Machining complimentary metals parts for assemblies
• Thread milling precision hole to hole accuracy for inserts installations
• Positional and alignment boring
• Surface enhancement and profile machining
• Precision machining for enhancing fixtures

Achievable Accuracies

With this CNC process, we can achieve a positional tolerance of ±0.005” or 0.001 “/”, whichever is greater. Hole size accuracy is typically to ±0.001”. Tighter tolerances are achievable with the careful oversight of our CNC machining experts.

Application Examples

Jigs & Fixtures
A popular application for this process are jigs and fixtures. We commonly build manufacturing aids with FDM that are light weight, ergonomically enhanced and even custom to users. Depending on the complexity of the jig or fixture, they may require CNC machining to line bore parts for alignment, mill for smooth surfaces or machine complementary metal parts.

Sometimes for our own internal manufacturing purposes, we create holding fixtures for parts that need machining in order to ensure accuracy. We can design fixtures and nesting tools to hold parts for machining with an assortment of processes and materials.

Complementary Parts
Another application is when parts require complementary metal parts or plastic parts in a different material. These assemblies can be achieved mid-build with technologies like FDM by pausing prints and embedding machined metal or plastic parts into the incomplete component.

Design Considerations

The hybrid method of using CNC machining with FDM requires specific design considerations:

• Build with Additional Material
• Additional material needs to be built into raw 3D printed parts so that when they’re machined, there are enough layers to remove to achieve the correct dimensions.
• Note Areas of Tight Tolerance
• When consulting with your project engineer, be sure to note the critical dimensions that need to be machined. That way engineers can design adjustments to optimize the build for machining, such as increasing certain wall thicknesses or going up a tip size.

The value of 3D printing is fully realized when its design freedoms and speed is married to the cost effective methods of conventional manufacturing. CNC machining offers to customers the ability to take advantage of FDM’s benefits while maintaining high tolerance requirements.