01
Heat builds up and the part melts
PP has low thermal conductivity, so heat stays at the cutter. Chips weld to the flute, the edge drags, and you get smeared walls or a melted corner. The part looks fine until you measure it.
Plastic CNC Machining
PP Polypropylene Parts, Precision CNC Machined
We machine PP and HDPE for parts that need to survive acids, solvents, and repeated flexing. Tolerances hold at ±0.005 mm on the right geometry. Send a CAD file and get DFM feedback with pricing.
±0.005 mm toleranceRa 0.8–1.6 μm finishFrom one part to 10,000+12-hour quote and DFMISO 9001:20153–5 day shipping
127High-precision CNC machines
15 yearsin CNC machining since 2011
99.99%Qualification rate
7,600 m²Manufacturing space across 3 plants
Common problems
Why PP parts fail after machining
PP is not hard to cut. It is hard to cut without melting, warping, or scrapping the batch.
02
Wall thickness moves after machining
Stress locked into an extruded PP plate releases once you remove material. A bracket that was flat at 9 a.m. can bow overnight. Tight walls finish oversize or undersize depending on which side you cut first.
03
Soft material grabs the drill
PP is gummy. Standard twist drills pull in, drill oversized holes, and leave a burr you cannot deburr cleanly. Hole position drifts on deep bores and mating hardware no longer fits.
04
Surface finish looks machined, not sealed
A tool mark left on a fluid-handling part becomes a leak path. If the finish is not controlled, gaskets do not seal and cleaning agents collect in the grooves. Cosmetic passes do not fix that.
Our approach
How we hold PP parts to drawing
Tooling, feeds, and fixtures chosen for soft plastics — not borrowed from an aluminum job.
Cutting strategy
Sharp tooling and high rake, run fast
PP cuts clean when the tool is sharp and the chip leaves the zone before heat soaks into the part. We run single-flute and two-flute carbide cutters with high rake angles, climb milling for the finish pass, and air blast instead of flood coolant. The air clears chips and keeps the workpiece cool without coolant soaking into the material.
Feeds and speeds are set per geometry, not per material name. A thin rib runs slower than a solid block. We leave 0.3–0.5 mm for the finish pass and take it in one continuous move so the surface does not show start-stop marks.
- 1Single-flute and two-flute carbideFree chip evacuation, less rubbing, less melt
- 2Air blast coolingNo coolant absorption, no swelling before measurement
- 3Climb milling on finishingCleaner walls on thin sections and long pockets
Stress control
Rough, relax, then finish
Machined PP moves. We rough with 0.5–1.0 mm stock on all faces, let the part sit, then finish. For parts with wall thickness under 3 mm or long unsupported spans, we run a separate stress-relief step before the finishing pass. This is the difference between a bracket that stays flat and one that bows in a week.
Fixtures matter as much as the cutter. Soft jaws and vacuum plates distribute clamping force so the part is not squeezed out of tolerance while it is being cut. We check the setup on the first article, not on the last.
- 1Rough with 0.5–1.0 mm stockRemoves bulk stress before the finish pass
- 2Stress relief for thin wallsKeeps flatness on sections under 3 mm
- 3Soft jaws and vacuum workholdingLow clamp pressure, no crush marks
Material selection
PP vs HDPE vs POM: pick the right plastic
PP is not always the answer. Use this to check the fit before you commit a design.
| Material | Best for | Watch out for |
|---|---|---|
| PP (polypropylene) | Chemical tanks, fluid parts, living hinges | Low stiffness; long unsupported spans flex |
| HDPE | Wear strips, cutting boards, low-friction guides | Softer than PP; tight tolerances drift |
| POM (acetal) | Gears, bushings, precision mechanical parts | Poor acid resistance; not for chemical service |
| PVC | Pipes, fittings, outdoor chemical exposure | Machining dust needs extraction; limited colors |
| PEEK | High-temperature and sterile applications | Higher cost; slower to machine than PP |
What we do
Plastic CNC services around PP
One shop for the prototype and the production run, with the same inspection standard on both.
01
3-axis CNC milling
Flat plates, housings, covers, and manifold blocks. 27 machines for straightforward geometry at volume.
02
4-axis CNC milling
Parts with features on multiple faces. 12 four-axis mills cut down on refixturing and repositioning error.
03
5-axis CNC machining
Complex contours and undercuts in one setup. 16 simultaneous 5-axis centers hold position on curved surfaces.
04
CNC turning and mill-turn
Bushings, sleeves, and threaded plastic parts. 16 mill-turn centers combine turning and milling in one cycle.
05
Rapid prototyping
Fit checks and design reviews before tooling. Same material as production so the test is real.
06
Surface finishing
Bead blasting, tumbling, and polishing for sealing surfaces and controlled cosmetic finish.
Capability range
Machine capacity and inspection scope
What we can take on for PP and other plastics, stated plainly.
| Item | Specification |
|---|---|
| Tolerance | ±0.005 mm on controlled features |
| Surface finish | Ra 0.2–0.8 μm fine, Ra 0.8–1.6 μm standard |
| Maximum part size | 4,000 mm maximum processing size |
| Large travel | 4,000 × 400 × 150 mm |
| Medium travel | 750 × 1,150 × 550 mm; 600 × 600 × 600 mm |
| Compact travel | 500 × 500 × 450 mm; 500 × 310 × 200 mm |
| Rotary table | Ø400 mm rotary table |
| Inspection | 100% inspection before shipment; reports on request |
Why GreatLight
What we bring to a PP job
Numbers first. The rest is process discipline.
15Y
Machining since 2011
Fifteen years of cutting plastics and metals. The feeds and fixtures for soft material are already worked out.
127
CNC machines on site
16 simultaneous 5-axis centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers.
1
Part to 10,000+
No minimum order quantity. One prototype and a 10,000-part run use the same inspection standard.
12h
Quote and DFM feedback
CAD files reviewed and priced within 12 hours. Production can start within 24 hours of approval.
4
Certifications held
ISO 9001:2015, IATF 16949:2016, ISO 13485:2016, and ISO 27001:2022.
100%
Inspection before shipment
Raw material check, in-process monitoring, final inspection. Dimensional reports on request.
±0.005 mmTolerance on controlled features
99.99%Qualification rate
150Technicians across 3 plants
<2%Historical late-delivery probability
Industry fit
Where PP parts go
Automotive & EV
Underhood brackets and fluid-adjacent housings in PP. Chemical resistance and vibration fatigue both matter.
- ±0.005 mm
- 100% inspection
- IATF 16949
Electronics
Insulating fixtures, trays, and connector bodies. PP keeps dielectric behavior stable and resists cleaning solvents.
- Ra 0.8–1.6 μm
- No minimum order
- ISO 9001
Industrial machinery
Chemical tanks, wear strips, and pump components. Material selection is checked against the fluid list before machining.
- 4,000 mm max size
- Material certs
- Batch traceability
Medical devices
Non-sterile fixtures and fluid-path prototypes in PP. Finish and cleanliness requirements are set before the first cut.
- ISO 13485
- Ra 0.2–0.8 μm
- Inspection reports
FAQs
Questions engineers ask about PP machining
Can PP really hold ±0.005 mm?
Yes, on features that are supported and not too thin. The tolerance applies to controlled dimensions after the part has settled, not to a freshly cut wall that is still releasing stress.
Where the geometry is thin or long, we say so during DFM review and propose a realistic tolerance. Claiming ±0.005 mm on a 200 mm unsupported PP span would be dishonest.
Which PP grade should I specify?
For most machined parts, standard homopolymer or copolymer PP plate works. If the part sees UV, specify a UV-stabilized grade. If it sees continuous heat, check the service temperature against the application before choosing PP over PEEK or PVC.
Send the chemical list and operating temperature with the CAD file. Material selection is part of the DFM feedback, not an afterthought.
How do you stop the part from melting?
Sharp high-rake carbide tooling, single or two flutes, climb milling on the finish pass, and air blast instead of flood coolant. Feeds and speeds are set per feature.
A thin rib runs slower than a solid block. Chip evacuation matters more than spindle speed on soft plastics.
Why do my PP parts bow after machining?
Stress in the plate releases when you remove material. Machining one side fully before the other makes it worse.
We rough both sides, leave 0.5–1.0 mm, let the part relax, then finish. For walls under 3 mm we add a stress-relief step before the final pass.
Can you hold a sealing surface finish?
Yes. Sealing surfaces are finished to Ra 0.8–1.6 μm as standard, and Ra 0.2–0.8 μm where a finer finish is required.
Tell us where the gasket lands on the drawing. A controlled finish on that face is more useful than a cosmetic polish across the whole part.
What is the smallest and largest part you can run?
There is no minimum order quantity, so one prototype is fine. At the other end, 4,000 mm maximum processing size is available on the large-travel machines.
Compact work goes on 500 × 500 × 450 mm and 500 × 310 × 200 mm machines. The right machine is picked by geometry, not by convenience.
How fast can I get parts?
Quote and DFM feedback come back within 12 hours. Production can start within 24 hours of approval, and parts ship in 3–5 days.
The historical late-delivery probability is below 2%. If a schedule is tight, say so early and we will confirm what is realistic.
Do you sign an NDA?
Yes. Uploads are secure and confidential, and an NDA is available on request.
Send the NDA before the CAD files if your process requires it. Nothing is shared outside the job.
Send your PP part for a quote
Upload a CAD file and get pricing plus DFM feedback within 12 hours. No minimum order quantity, 100% inspection before shipment.
12-hour quote100% inspectionNo minimum order quantityNDA on request
