Plastic Melting Point Chart: A Guide for CNC Machining Materials

Technician checking cutter heat while CNC milling engineering plastic stock

Quick answer

Use melting point (and glass transition / HDT) to set speeds, feeds, coolant strategy, and material shortlists—not as a single “max service temperature.” On the mill, local friction can soften a polymer long before the bulk melting point. Pair this chart with duty temperature and tolerance needs.

Melting point charts are useful—until someone treats Tm as a machining speed limit or a continuous-use rating. In CNC plastics, heat at the tool edge, chip evacuation, and crystallinity matter as much as the datasheet number. Below is a practical chart of common CNC polymers and how to use those numbers on the shop floor.

What “Melting Point” Means for Polymers

Semi-crystalline plastics (POM, PA, PE, PP, PEEK, PTFE family behavior differs) show a melting range tied to crystal structure. Amorphous plastics (PC, PMMA, many PEI/PSU grades in practice for processing) soften through glass transition without a sharp melt the same way. When a chart lists a melting point for an amorphous grade, treat it as a processing reference and lean on Tg / HDT for design.

For a high-performance deep dive, see what PEEK’s melting point means in machining. For fluoropolymers, compare PEEK vs PTFE selection and PTFE temperature limits.

Plastic Melting Point Chart for CNC Materials

Values are typical literature ranges for common unfilled grades—always verify the specific stock certificate.

Material	Approx. Tm / process ref.	Shop note for CNC
HDPE	~125–135°C	Soft, gummy if heat builds; sharp tools, cool air/coolant
PP	~160–170°C	Similar soft-chip risk; watch long stringers
POM (acetal)	~165–175°C	Machines cleanly; rubbing still melts the kerf
PA6 / PA66	~220°C / ~260°C	Dry first; heat + moisture = warp
PET / PET-P	~250°C class	Good precision; manage heat on finish
PC (amorphous)	Tg ~145°C (no true Tm)	Stress-crack risk; sharp tooling, gentle feeds
PMMA	Tg ~100–110°C	Brittle chip; polish strategy matters
PPS	~280°C	Abrasive filled grades; carbide + dust control
PEEK	~343°C	High heat capacity; see dedicated PEEK guide
PTFE	~327°C	Soft, cold-flow; poor chip, special tooling habits
UHMW-PE	~130–136°C	Very tough chip; slow heat soak, sharp cutters
PVDF	~170–180°C	Chemical duty; moderate machining heat care

Why Melting Point Matters on a CNC

Surface melt / reweld: dull tools or clogged flutes smear polymer back onto the wall
Tolerance theft: heat expands the part during the cut; it shrinks after cool-down
Crystallinity damage: overheating semi-crystalline zones can change wear and chemical behavior
Fixturing: soft plastics deflect; heat makes deflection worse

Shop tip: If chips look shiny and ropey instead of crisp, you are likely generating melt at the edge—raise sharpness, improve evacuation, or reduce rub, not only “spindle RPM.”

HDT vs Melting Point

Heat deflection temperature estimates when a material softens under load. Melting point estimates when crystals break down in processing. For service design, HDT and continuous-use ratings usually beat Tm. For machining, both matter: Tm warns about chip melt; HDT reminds you the part can creep in a hot fixture. See also PPS vs PEEK high-temperature comparison when the duty is truly hot.

Best Practices by Melting / Softening Class

Lower-melt commodity plastics (PE, PP, UHMW)

Prioritize sharp geometry, light finish passes, and aggressive chip clearing. Climb milling often helps surface quality.

Engineering plastics (POM, PA, PET, PC)

POM loves high surface speed with clean chips. Nylon needs dry stock—see POM vs nylon machining differences. PC wants sharp tools and avoidance of solvent stress cracking after the job.

High-performance (PPS, PEEK, PEI, PTFE)

Expect abrasive fillers, expensive scrap, and heat management discipline. PEEK in particular stores heat in the cut—feed enough to make a chip, not dust.

Frequently Asked Questions

Can I machine above the melting point with coolant?

Bulk coolant does not save you if the tool edge is rubbing. The local interface can still melt. Fix the cut, do not drown a dull tool.

Is higher melting point always better?

No. Higher Tm materials can still be abrasive, anisotropic, or expensive to hold flat. Match polymer to duty, then tune the process.

Where does density fit in?

Density drives part weight and can hint at filled grades. Use the CNC plastic density chart alongside this melting chart.

Conclusion

A melting point chart is a starting map for CNC plastics: it frames how easily a polymer will smear, how much heat the process can tolerate, and which materials belong on a high-temp shortlist. Combine Tm with Tg/HDT, filler type, and tolerance strategy—then machine with sharp tools and intentional chip load.