When to Use Plastic in CNC Machining — And What It Really Solves 

Summary:

Plastic isn’t a compromise — it’s a strategy. CNC plastic parts like Delrin or ABS aren't about cutting corners. They help teams move faster, test smarter, and avoid costly design traps before metal ever hits the machine. 

We don’t talk about plastic in CNC machining because it sounds impressive.
We talk about it because it solves problems that metal can’t — not technical ones, but process ones.

Maybe your prototype cost is too high.
Maybe you're on your third revision and still waiting for the first metal part.
Maybe you're guessing too much and learning too little.

This is where CNC plastic parts become more than a workaround.
They become a way to break the loop, learn faster, and buy time without losing precision.

Plastic Isn’t a Downgrade — It’s Tactical Breathing Room

When teams switch to plastic, it’s rarely because they think it’s “better.”
They do it because they’re under pressure.

  Too much time wasted waiting for aluminum
  Too many design changes still in flux
  Too little budget to make mistakes in metal
  Too few answers about how it all fits together

CNC plastic machining, when used properly, creates a feedback loop between idea and action. You machine. You test. You adjust. You do it again. And each cycle costs less — in money, in lead time, in anxiety.

That’s the value most people don’t see until they’ve been burned once.

CNC Delrin Is the Plastic Engineers Trust

Not all plastics behave in CNC like engineers expect. Some melt. Some clog cutters. Some flex or fuzz at the edges.

Delrin (also known as POM or Acetal) avoids almost all of that.

It machines like a dream — clean, rigid, and dimensionally reliable

You can tap threads, hold tolerances, even ream holes cleanly

It’s chemically stable and moisture-resistant

It gives you "aluminum-like behavior" without the cost or commitment

Teams we work with use CNC Delrin parts to prototype bearings, gears, brackets, sliders, and jigs. Not because they’re temporary — but because they work.

ABS Is Not a Substitute — It’s a Purpose-Built Shortcut

You’ve probably worked with ABS in 3D printing or molded parts. In CNC machining, it plays a different role.

ABS is softer, easier to deform, and doesn’t love sharp edges or high tolerances. But when you're testing shape, enclosure fit, interface layout — ABS machining makes a lot of sense.

It's cheap.
It's familiar.
It's fast.

You just need to know its limits:
Don’t load it. Don’t expect mirror finishes. Don’t over-tighten anything.

Plastic Is About Progress, Not Perfection

The mistake many teams make is assuming plastic should act like metal — just lighter.

Wrong expectation.

The teams that succeed with CNC plastics are the ones who use it to:

Validate assembly paths before committing to castings

Prototype mechanical function with real materials

Test form and tactile feel without cutting metal

Send parts to clients faster than 3D prints can ship

We’ve helped teams reduce NPI cycles from 4 weeks to 7 days just by machining Delrin instead of waiting on aluminum. That’s not because plastic is magic. It’s because the timeline became a tool — not a bottleneck.

Real-World Use Case

A startup designing a medical device contacted us for CNC aluminum parts. But after reviewing their needs — testing internal layout, snap fit behavior, and thermal spacing — we recommended switching to Delrin.

They got their parts in 3 days.
Found a design flaw within 24 hours.
Re-submitted a revision that went straight to tooling.

Without that one CNC plastic run, their aluminum design would’ve shipped flawed.
That’s the hidden cost they avoided — by thinking strategically, not traditionally.

Ready to Try It?

You’re not choosing a material. You’re choosing how fast you learn.

If that matters to you —
Send us your part. Tell us what you want to know.
We’ll help you decide if Delrin, ABS, or a smarter hybrid is the way forward.

Tools and Resources

Upload your plastic part for CNC review →
Delrin material profile and use cases →
Use our tolerance calculator for plastics →

FAQ

Is plastic suitable for structural CNC parts?
Only in low-stress conditions. Delrin performs well in fixtures and low-load components, but metal is better for structural integrity.

Why use CNC plastic parts instead of 3D printing?
For higher dimensional accuracy, real engineering-grade material behavior, better surface finish, and repeatable results.

What’s better — Delrin or ABS?
Delrin, if you're testing function or mechanics. ABS, if you’re testing form, shape, or layout at minimum cost.

Can I prototype a metal part in plastic?
Absolutely — that's one of the smartest things you can do to avoid costly redesigns later.

Does using plastic actually reduce cost?
Often yes, but the real benefit is speed and reduced risk. One plastic prototype can prevent weeks of metal mistakes.

Author’s Note

This article was created by the EKINSUN CNC engineering team, based on real client projects where plastic machining helped solve problems faster, smarter, and with fewer downstream regrets. Whether you're prototyping for speed or looking for early design truth, we’re here to help you make the right call — before the metal chips fly.