CNC Machining Plastic Parts: Cut Scrap and Rework Costs

When we first started machining plastic parts for medical and automation customers, our scrap rate was nearly 18%. Warping, burrs, melting edges, and tolerance drift caused constant rework.

After 3 years of process optimization, we reduced scrap to below 4%, shortened cycle time by 22%, and saved customers thousands of dollars per batch.

If you are sourcing CNC machining plastic parts, this guide will show you exactly how to lower scrap, avoid rework, and choose the right machining strategy.

Many buyers assume plastic is easier than metal.
In reality, plastics are more sensitive to heat, clamping pressure, and tool wear.

From our workshop experience, 90% of defects come from:

 Each extra setup or rework increases unit cost 15–30%.

Material choice directly affects stability and yield rate.

From our real production data:

✅ Tip: For tight tolerance ±0.02 mm, we strongly recommend POM or PEEK.

This is where most factories lose money.

Incorrect speeds cause melting instead of cutting.

Our tested parameters:

 Real case:
Switching from flood coolant to compressed air cooling reduced surface burns by 70%.

Plastic deforms easily under pressure.

We replaced metal vises with:

• ✔ Soft jaws

• ✔ Vacuum fixtures

• ✔ Low-pressure clamps

Result:
Flatness improved from 0.15 mm → 0.04 mm, rework almost eliminated.

Plastic machining needs sharper tools than metal.

Our internal rule:

• Aluminum tool life: 3–5 days

• Plastic tool life: 1–2 days only

If you push tools longer → burrs + scrap surge.

Small tool cost = big quality savings.

Customer: Automation equipment manufacturer
Material: POM
Qty: 12,000 pcs/month

Before optimization:

• Scrap rate: 16%

• Rework time: 40 hours/week

• Unit cost: $2.10

After optimization:

• Scrap rate: 3.8%

• Rework: 8 hours/week

• Unit cost: $1.62

 Total saving: $5,700/month

If you're buying CNC plastic components, check these 6 things:

• ✔ Plastic machining experience >5 years

• ✔ Dedicated plastic tools

• ✔ Temperature-controlled workshop

• ✔ First Article Inspection (FAI)

• ✔ CMM inspection report

• ✔ Scrap rate transparency

• ✖ Only metal machining background

• ✖ No process documentation

• ✖ Cannot provide tolerance history

• ✖ Extremely low price (usually means high scrap)

Cheaper machining often costs more in the long run.

POM (Delrin) offers the best stability, low friction, and low scrap rate.

Use high feed rate, sharp tools, and air cooling.

For small batches (<5,000 pcs), CNC is more economical and flexible.

Typically ±0.02–0.05 mm depending on material.