Plastics in CNC Machining: When to Choose ABS, PEEK, or Delrin

CNC machining isn’t limited to metals. Plastics play a vital role in producing lightweight, cost-effective, and high-performance components across many industries.
Three of the most widely used plastics in CNC machining are ABS, PEEK, and Delrin—each with specific properties, machining requirements, and use cases.

Whether you're prototyping enclosures, manufacturing medical-grade implants, or designing functional industrial components, knowing when and why to choose the right plastic is critical for cost, performance, and reliability.

In this guide, we break down how ABS, PEEK, and Delrin compare and when each is the best choice for your CNC machining project.

Why Use Plastics in CNC Machining?

Plastics offer a combination of machinability, design flexibility, and material-specific advantages.

Compared to metals, plastics are:

• Lighter

• Easier to machine (lower tool wear)

• Non-conductive

• Chemically resistant

• Often more cost-effective

Plastics are widely used in aerospace, medical, electronics, automotive, and consumer product industries, especially during CNC prototyping machining when fast iteration is key.

Overview: ABS vs. PEEK vs. Delrin

ABS: Best for Prototypes, Enclosures, and General-Purpose Parts

What is ABS?

ABS (Acrylonitrile Butadiene Styrene) is a thermoplastic known for its affordability, ease of machining, and decent strength-to-weight ratio. It’s widely used in consumer electronics, automotive trim, and mechanical prototyping.

Why choose ABS in CNC machining?

• Highly machinable: Low cutting resistance and smooth finish

• Low cost: Ideal for cost-sensitive prototyping

• Good impact resistance: Tolerates everyday stress

• Paintable and glueable: Easily finished and bonded

• Non-conductive: Safe for housing electronics

Best applications:

• Control panels and user interface housings

• Lightweight mechanical prototypes

• Protective casings for sensors

• Custom brackets and jigs

• Visual or fitment models

When not to use:

Avoid ABS in high-heat, high-load, or chemically aggressive environments. It’s not suitable for long-term mechanical parts under stress.

PEEK: Best for High-Performance, Medical, and Aerospace Components

What is PEEK?

PEEK (Polyether Ether Ketone) is a high-performance thermoplastic that offers outstanding strength, thermal resistance, and chemical stability. It’s biocompatible and suitable for highly regulated industries.

Why choose PEEK in CNC machining?

• High heat resistance (250°C): Suitable for autoclaves and engines

• Mechanical durability: Resists wear, fatigue, and abrasion

• Biocompatibility: Approved for implants and medical instruments

• Chemical resistance: Stable in aggressive environments

• Low outgassing: Ideal for aerospace and cleanroom use

Best applications:

• Spinal cages and orthopedic implants

• Aerospace brackets and electrical insulators

• Heat-resistant medical device components

• Oil and gas valve seats

• Semiconductor handling tools

Machining considerations:

PEEK is harder and more expensive to machine than ABS or Delrin. It requires sharp tooling, low feed rates, and careful temperature control to avoid stress cracking or delamination.

When not to use:

Avoid PEEK when cost is a major concern or when the application doesn’t require high-performance characteristics. For general-purpose parts, it's overkill.

Delrin: Best for Low-Friction, High-Wear Mechanical Parts

What is Delrin?

Delrin (also known as Acetal or POM) is an engineering plastic known for its low friction, excellent dimensional stability, and moisture resistance. It combines the strength of metal with the ease of machining plastic.

Why choose Delrin in CNC machining?

• Low friction: Excellent for sliding components

• High stiffness and tensile strength: Good for mechanical loads

• Low water absorption: Stable in wet environments

• Excellent wear resistance: Long-lasting under mechanical stress

• Good surface finish: Ideal for precision parts

Best applications:

• Bushings, bearings, and washers

• Gear wheels and cams

• Electrical insulators

• Medical delivery systems (non-implant)

• Locking mechanisms and latches

Machining considerations:

Delrin machines cleanly and fast. However, it can warp during cooling if internal stress isn’t managed. It’s best to avoid deep pockets or thin walls unless properly supported during cutting.

When not to use:

Avoid Delrin for parts requiring bonding or painting—adhesion is poor. It’s also not suitable for extreme heat or chemically aggressive environments.

Choosing the Right Plastic for Your CNC Project

Each plastic offers distinct advantages. The best choice depends on functional requirements, environmental exposure, mechanical load, and regulatory standards.

Use ABS when:

• You need fast, affordable prototypes

• Cosmetic appearance or fitment testing is the goal

• The part will operate under moderate stress and temperature

Use PEEK when:

• Parts will be sterilized or implanted in the body

• Components need to withstand extreme heat or chemicals

• Maximum strength and durability are critical

Use Delrin when:

• Your part needs to slide or rotate against another surface

• Long-term wear and dimensional stability are priorities

• Low friction and high stiffness are required

Real-World Industry Examples

In Medical:

• PEEK is used in spinal implants and surgical tools

• Delrin is common in diagnostic housings and sliding valves

• ABS may be used in prototype versions of surgical trays

In Aerospace:

• PEEK serves in high-heat shielding and insulation

• Delrin functions in actuating components and fittings

• ABS is used in form-fit-function models before metal replacement

In Consumer Products:

• ABS for wearable device casings

• Delrin for internal mechanical movement parts

• PEEK for specialized high-heat applications like kitchenware or electronics

Final Thoughts

The choice between ABS, PEEK, and Delrin in CNC machining boils down to performance vs. cost.
ABS is great for fast and affordable prototypes, PEEK is unmatched in demanding, regulated environments, and Delrin sits comfortably in the middle for mechanical and wear parts.

Working with an experienced CNC prototyping machining service can help ensure the right material is chosen based on your exact requirements, whether you’re prototyping or moving into production.