In Machining & Fabrication

Machining Thermoset Plastics: Challenges, Tooling, and Best Practices

Machining Thermoset Plastics: Challenges, Tooling, and Best Practices
If you’ve worked with thermoset plastic parts before, you know that thermoset is strong. So strong, in fact, that a thermoset part can’t be reheated or reworked; machining is the only option. And the machining has to be right the first time around.

While many industries depend on thermoset components, there are some considerations: thermosets add more wear to your tools, create dust, and lead to unrecoverable scrap. Here’s how Dielectric handles each of these issues.

Key Takeaways

  • Reinforced thermosets wear down tools faster than thermoplastics because they’re harder and contain glass fiber.
  • A thermoset mistake can’t be remelted or recycled, so first-pass accuracy and material yield matter.
  • Dust is the primary shop-floor issue (rather than heat), so dust collection at every machine is essential.
  • With thermosets, a tolerance of .005″ is typical, and tighter is possible depending on part design.

Why Thermosets Are Hard to Machine

Why work with thermosets if they can be difficult to machine? There are many times when thermoset plastics offer the best solution.

Thermosets earn their place because of what they can handle. Depending on the application, a part may need mechanical and impact strength, or the ability to withstand high temperatures on industrial machines. Thermosets also insulate very well and don’t conduct electricity. That’s why they’re typically used in electrical distribution, which branches into defense, industrial manufacturing, and industrial machinery.

Other properties vary by material. Some thermosets absorb moisture, and some don’t. FR-4 brings fire resistance. And some grades are UL recognized, while others aren’t. The right choice depends on your application, which is why it helps to understand how these materials machine before you commit. Fortunately, at Dielectric we’re here to help you navigate.

Abrasiveness and Tool Wear

With notorious strength come some challenges. One of the biggest is abrasiveness, which means the material wears down cutting tools. Thermosets wear tools down faster than thermoplastics because the material is very hard and often reinforced with glass or fiber.

When thermosets are done being shaped, they’re done. There’s no second chance to melt it down or undo a component once it’s made. So, getting pieces properly and accurately planned is critical. If something is slightly off, it goes to scrap.

In some ways, tooling thermosets isn’t that different from thermoplastics. Both call for standard CNC tools. But the real difference is that the tools dull faster, so plan your tooling around replacement.

Dust Control and Shop Setup

Glass-laminated thermosets are extremely tough, but they can also create a tough-to-deal-with dust. The dust is similar to fiberglass: itchy and unhealthy.

Dust control can’t just be an afterthought. If a shop runs thermoset materials, they must make it a top consideration. At Dielectric, our dust collection system extends to every machine, capturing the dust while each component is made. Our facility stays very clean.

Shops may also run into some heat while machining, but fortunately, with thermosets, that’s not such a concern. Plastics don’t machine as hot as metals, making for easier handling in that sense.

Getting the Most Out of Every Sheet

Waste is another factor. Thermoset scrap can’t be melted down or recycled, so waste has to be planned for. Our goal is the highest possible yield of parts from each blank or flat sheet. We aim to use the material as efficiently as possible right from the beginning.

Waste planning matters for your budget too. If your parts only need half a sheet, then the other half goes back into our stock. You don’t need to pay for a full sheet of material that you didn’t use. Because the material can’t be recovered once it’s cut, this offers real cost savings to help you plan better.

Holding Tight Tolerances

Tolerance is how much a finished dimension is allowed to vary from the spec. For thermosets, .005″ is typical, but keep in mind that’s a starting point, not a limit. What’s realistic depends on the design of the part and how you tolerance it. At Dielectric, we can exceed the typical number.

For more on how we work, see our fabrication and machining capabilities. For early-stage parts, see our prototyping services.

The Materials Behind the Machining

Much of our thermoset work centers on a handful of materials. FR-4 is a glass-epoxy laminate known for mechanical and electrical strength, and it’s the fire-retardant grade of G-10. GPO-3 is a fiberglass-reinforced polyester sheet used for electrical insulation. Phenolic is a hard, heat-resistant thermoset often used in electrical and structural parts, and G-11 is a higher-temperature glass-epoxy grade for parts that run hot. Each material is a little different, and each suits different applications.

Most of the time, we get designs from people who know exactly what they’re doing. The material they’ve specified is the right one, and there are no surprises. Once in a while, though, we’ll suggest a different grade to the client because it’s a better fit with the application.

While those conversations are rare, they’re important and part of how we work at Dielectric. If you need a second opinion or advice about the right grade, our team is here to help. Bring us your toughest parts.

Getting it Right with Dielectric

FR-4 and GPO-3 make up about 75% of our thermoset work. We machine these thermoset materials every single day. That familiarity and experience are built into our work. We have an ISO 9001 certification and a very clean shop. Our customers rely on us for parts that come out right for our electrical distribution, defense, and industrial machinery.

A few habits make a big difference when working with thermosets:

  • Plan your tooling around frequent replacement, since thermosets dull tools faster than thermoplastics.
  • Collect dust at every machine, because fiberglass-type dust is itchy and unhealthy.
  • Lay out parts for the highest yield from each sheet, since scrap can’t be recycled.
  • Confirm the grade fits the application before you commit, since a thermoset part can’t be reworked.
  • Know your tolerance: about .005″ is typical, and tighter is possible depending on the part’s design.

We work in low-volume, high-mix runs, meaning many different part types made in small quantities. Whether you need a single prototype or a mix of parts, we’re glad to take a look.

If you’ve got a thermoset part that’s giving you trouble, whether it’s tight tolerances, a tricky material, or scrap you can’t afford, we’d like to see it. Send us your drawing, and we’ll tell you how we’d approach it. Request a quote to get started.