When to Use Plastic in CNC Machining: The Speed & Cost Strategy Product Managers Miss 

The Problem Nobody Talks About

You're developing a new product. Engineering says they need metal parts. Marketing says you need them in 2 weeks. Your budget is already stretched. Reality: you're stuck.

The trap most teams fall into: They assume metal = production-ready. So they machine aluminum for prototyping. They wait 4-6 weeks. They test it. They find a design flaw. They iterate. Another 4-6 weeks. Meanwhile, your launch timeline slips, and you've burned through the prototype budget.

Here's what you're missing: Plastic CNC machining isn't a cheap substitute. It's a strategic tool. When used correctly, it cuts your NPI (New Product Introduction) timeline from 8-12 weeks to 2-3 weeks. You catch design problems 60 days earlier. You arrive to market on time.

This article explains when and why CNC plastic parts solve problems that metal can't.

Why This Matters for Your Timeline (The Real Numbers)

For cost-effective plastic prototyping, ABS is one of the most affordable choices, offering good machinability and durability, and as a general rule, plastic materials are cheaper than metal.

But the real benefit isn't cost—it's speed. And this is where most suppliers fall behind.

Typical timeline comparison:

Phase                       Metal (Aluminum)           Plastic (Delrin/ABS) Standard                      Plastic with EKINSUN

Design → Quote          3-5 days                                    1-2 days                                                    Same day

Machining                   2-3 weeks                                  5-7 days                                                     1-3 days

Testing/Iteration          1-2 weeks                                  2-3 days                                                     24 hours

Total to First Result   4-6 weeks                               1-2 weeks                                                   3-5 days

What this means: Most suppliers quote plastic in 5-7 days. We quote same-day and ship within 24-72 hours. You're testing in 3-5 days instead of 2+ weeks. That's not just faster—that's a competitive advantage.

Plastic vs. Metal: Make the Strategic Choice

Don't think of plastic as "cheaper metal." Think of it as a different decision point in your development timeline.

       Need                                                         Best Option                                       Why

Testing form, fit, assembly                          Plastic (ABS/Delrin)              Speed matters more than strength

Validating mechanical function                  Plastic (Delrin)                       Real material behavior, 70% faster

Catching design flaws early                        Plastic (Both)                         Iterate cheaply before metal commitment

Final production part                                   Metal (Usually)                     Strength, durability, material traceability

High-load or structural                                Metal (Required)                   Plastic fails under stress

Real-world scenario: A medical device startup designed an assembly housing. They built it in Delrin first (3 days, $400 total). Testing revealed a snap-fit wasn't accessible. Revision took 1 day. Then they committed to aluminum tooling—confident the design was sound. Total savings: $15,000 in avoided aluminum rework and 6-week timeline compression. 

The Two Plastic Winners: Delrin (POM) vs. ABS

Delrin (POM/Acetal): For Function Testing

What it does: Machines like dream. Plastics like ABS or POM are cheaper than metals and work well for non-structural prototypes. Rigid, dimensionally stable, and reliable.

Best for:

• Mechanical parts: gears, bearings, sliders, jigs

• Parts requiring tight tolerance (you can hold ±0.02mm)

• Threading and threaded inserts

• Anything that needs to move or rotate

Cost: $30-80 per part (simple geometry)

Lead time: 5-7 days for prototype runs (industry standard) | 24-48 hours with EKINSUN

The catch: Not for high heat or outdoor use. Delrin softens around 150°C.

ABS: For Form & Layout Testing

What it does: Softer, easier to work with, extremely affordable. ABS, nylon and PTFE cost about the same as aluminum 6061.

Best for:

• Enclosure fit and layout

• Visual/tactile prototypes

• Design validation (shape, button placement, cable routing)

• Budget-conscious rapid iteration

Cost: $15-40 per part

Lead time: 3-5 days (standard) | Same-day quote, next-day delivery with EKINSUN

The catch: Lower strength, less precise than Delrin. Don't load it or expect mirror finishes.

Quick rule: Delrin if you're testing how it works. ABS if you're testing how it looks and fits.

When Plastic Actually Fails (Be Honest About Limits)

Not every design should be prototyped in plastic. Using plastic where metal is required wastes time and money.

These applications need metal from the start:

• High-stress structural parts – Plastic creeps and deforms under sustained load

• Outdoor exposure – UV and weather degrade plastic; metal is stable long-term

• Repeated threading cycles – Threaded inserts loosen in plastic; metal threads stay tight

• Tight flatness requirements – Plastic warps if not perfectly supported

• Extreme temperatures – Most plastics lose strength above 80-100°C

Real failure story: A startup prototyped a mounting bracket in ABS to save cost. In thermal testing at 50°C, it warped by 2mm—non-functional. They ordered aluminum (right choice, wrong timing). 3-week delay. Cost them their launch window.

The lesson: Understand your part's actual requirements before choosing plastic. Cutting corners on material choice amplifies problems downstream.

The Secret: Using Plastic as Your Competitive Advantage

Smart product teams use CNC plastic strategically. But there's a hidden layer: when you can compress testing to days instead of weeks, you move faster than competitors.

Your timeline with EKINSUN (express plastic): Monday morning: CAD sent. Same-day quote received. Tuesday morning: First prototype delivered. You test it. Find issue with snap-fit geometry. Wednesday: Revised CAD submitted overnight. Thursday morning: Revised part arrives. Confirms fix works. Friday: Design locked. Submit to aluminum tooling for production run. 2 weeks later: First aluminum pilot run. Production-ready.

Competitor's timeline (standard supplier, 5-7 day lead time): Week 1: Waiting for plastic quote and delivery. Week 2: First plastic sample arrives. Design flaw discovered. Week 3: Plastic revision ordered. Week 4: Revised plastic tested. Design locked. Finally submit to aluminum tooling. Week 7-8: First aluminum samples. Production-ready.

Your advantage: You're already in production while competitor is still prototyping. That's a 3-4 week market advantage—often worth more than the entire prototype budget.

The Questions to Ask Before Choosing Plastic

1. Is this part structural or cosmetic/functional?

   • Structural = metal (likely)

   • Functional/cosmetic = plastic works

2. What's my real deadline?

   • Less than 4 weeks to first prototype? → Plastic

   • More flexibility? → Could do metal

3. How many design iterations am I expecting?

   • 2+ iterations expected? → Plastic saves money

   • Single iteration? → Could go straight to metal

4. What's my budget for prototyping?

   • Tight budget? → Plastic (50-70% cheaper per unit)

   • Flexible? → Either works

5. Does this part handle loads or temperature stress?

   • Yes → Metal required

   • No → Plastic is fine

Cost Reality: When Plastic Wins (And When It Doesn't)

Plastic wins when:

• You need 1-5 prototypes for testing ($200-500 total vs. $2,000-5,000 in aluminum tooling)

• Design is still in flux (changes cost pennies in plastic, thousands in metal)

• Timeline is under 3 weeks (plastic machines 70% faster)

Metal wins when:

• You need 50+ units production-like behavior ($50-150/unit in metal, similar cost in plastic but only if you're certain design is locked)

• You require material traceability (medical/aerospace)

• Part must perform under stress (plastic not suitable)

Your Timeline Decision Framework

Scenario A: Prototype Phase (Uncertain Design) → Use plastic (Delrin for function, ABS for form) → Iterate 1-2 times → Lock design → Move to metal production

Scenario B: Design Locked, Need Production-Like Samples → Skip plastic → Go straight to aluminum CNC for pilot run → Faster path to production

Scenario C: Tight Timeline, Uncertain Design → Parallel track: plastic for quick testing + aluminum pilot simultaneously → Extra cost initially, but you hit market window

Real Client Example: From 8 Weeks to 2 Weeks

A consumer electronics company designed a device housing with snap-fits. They wanted to test assembly before committing to injection molding tooling ($50K investment).

What they did:

1. Sent CAD on Monday

2. CNC Delrin prototype delivered Thursday (3 days)

3. Assembly testing showed snap-fit too tight

4. Revised CAD, reordered Friday

5. New prototype arrived Tuesday

6. Confirmed design was now perfect

7. Submitted to injection mold tooling with confidence

Traditional path (metal aluminum):

1. Waited 2 weeks for aluminum prototype

2. Found snap-fit flaw in testing (week 3)

3. Aluminum revision took another 2 weeks

4. Finally locked design in week 5

5. Submitted to mold tooling

Result: CNC plastic allowed them to compress testing from 5 weeks to 1 week. They caught the design flaw while it was cheap to fix. Injection tooling proceeded risk-free.

What to Tell Your Engineer (And Your Budget)

To engineers: "We're using plastic for design validation. It's not the final part—it's proof-of-concept. We're trading material strength for timeline and learning velocity."

To budget holders: "Investing $500 in plastic prototyping prevents $10,000+ in metal rework delays. The ROI is 20:1 in favor of early testing."

The Bottom Line

CNC plastic machining isn't about being cheap. It's about being smart.

When your design is fluid, plastic gives you speed. When your timeline is tight, plastic gives you breathing room. When you want to catch mistakes early, plastic lets you fail fast and cheap.

Metal is your answer when you're certain. Plastic is your question when you're not.

Most product teams use plastic too late (after burning metal budget) or not at all (wishing they had moved faster). The winners use plastic strategically: test early, iterate fast, commit to metal with confidence.

Ready to Accelerate Your Timeline? (Days, Not Weeks)

If you're juggling prototype timelines, design iterations, and budget constraints, here's what EKINSUN brings to the table:

• Same-day quotes on plastic CNC parts (most suppliers: 1-3 days)

• 24-72 hour delivery on Delrin/ABS prototypes (most suppliers: 5-7 days)

• Experience across 1,000+ plastic projects so we catch design issues upfront

• No minimum order – 1 part or 100, same fast turnaround

Send us your CAD file and tell us:

• What are you testing? (Function? Form? Assembly?)

• When do you need it?

• Budget ballpark?

We'll provide a quote same-day and can often ship the next morning.

[Request Your Express Plastic Quote] – Response within 24 hours (usually 2 hours during business days).

FAQ

Q: Can I use plastic parts in the final product? A: Sometimes. For non-structural, low-stress, room-temperature applications, yes. For high-load or mission-critical parts, no. We'll advise based on your specs.

Q: How accurate is CNC plastic vs. CNC metal? A: Delrin holds ±0.02mm easily. Metal holds ±0.01mm. For most prototype testing, Delrin's accuracy is more than sufficient.

Q: What's faster—3D printing or CNC plastic? A: 3D printing is 1-2 days faster for geometry. CNC plastic is 2-3 days faster for accuracy and finish quality. For functional tests, CNC plastic usually wins.

Q: If I prototype in plastic, can I use the same design for metal? A: 95% yes, with minor adjustments. Some features that work in plastic (thin walls, complex undercuts) might need redesign for metal machining efficiency. We catch these during design review.

Q: What if my design needs threads? A: Delrin is excellent for threading and holds tight. ABS threads are weaker but work for light-duty. Metal is required for high-cycle threading applications.

Q: How do I decide between ABS and Delrin? A: Testing mechanical function? → Delrin. Testing shape and layout? → ABS. Need to hold tight tolerance? → Delrin. Budget-conscious? → ABS.

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.