PET CNC Machining

PET, or polyethylene terephthalate, is a semi-crystalline thermoplastic with good mechanical strength, excellent dimensional stability, low moisture absorption, and good chemical resistance to many oils, fats, and solvents. In CNC machining, PET is used for parts that need stiffness, wear resistance, and dimensional stability at moderate cost. It is also available in food-contact grades and in transparent forms, which expands its use into packaging, display, and fluid handling components. PET machines cleanly and holds tolerances well, making it a practical choice for precision mechanical parts in industrial and consumer applications.

Standard unfilled PET is the most common grade for machined parts, offering a balance of stiffness, strength, and machinability. Glass-filled PET offers higher stiffness and lower thermal expansion, making it suitable for structural components, though it is more abrasive to tooling. PET is also available in food-contact grades and in amorphous PET, which is transparent and used for display and packaging components. Copolyester grades such as PETG behave differently from crystalline PET, so the grade should be specified on the drawing because machinability and properties vary.

PET machines well, roughly comparably to acetal (Delrin) in terms of chip formation and surface finish, though it is slightly more abrasive and has a lower melting point than acetal. It cuts cleanly with sharp carbide tooling and produces manageable chips. Glass-filled PET is more abrasive and will wear tooling faster. The main challenges are heat management—PET softens at a relatively low temperature compared to high-performance plastics—and the potential for stress cracking on thin sections if clamping force is excessive. Overall, PET is considered easily machinable.

Standard machining holds ±0.02 to ±0.05mm. Precision work holds ±0.01mm on critical features. PET's low moisture absorption and good dimensional stability make it predictable for tight-tolerance work, better than nylon in that respect. The limiting factor is usually thermal expansion on larger parts and residual stress on thin sections. Stress-relief annealing before finish machining is advisable for parts with tight tolerances or complex geometry.

Yes, for parts with tight tolerances or thin sections. PET stock carries internal stress from the extrusion or molding process, and machining removes material unevenly, which can cause warping or stress cracking after machining. Annealing the stock before machining, and sometimes between roughing and finishing, reduces this risk. PET is also notch-sensitive, so sharp internal corners and thin walls should be reviewed during DFM and may benefit from additional stress relief.

As-machined PET has a smooth surface with visible tool marks, typically Ra 1.6 to 3.2μm. Bead blasting produces a uniform matte finish. Polishing can achieve a higher gloss where appearance matters. Because PET is often used in food contact and display applications, the surface must be cleanable and free of features that trap contaminants. PET's natural color is transparent to translucent white, and it can be supplied in opaque colors for specific applications.

Food and beverage: contact parts, filling equipment components, and conveyor components in food-contact grades. Industrial: wear strips, guide rails, and mechanical components where stiffness and dimensional stability are needed. Electrical: insulating components and spacers. Display and packaging: transparent components and structural parts. Fluid handling: pump and valve components for oils and fats. PET is often chosen where acetal's properties are adequate but a food-contact or transparent material is preferred.

PET and acetal both machine well and hold tolerances, but acetal has better dimensional stability and lower friction, making it the preferred choice for precision mechanical parts and bearing surfaces. PET offers better chemical resistance to some solvents and is available in food-contact and transparent grades. PETG is amorphous and transparent, easier to machine than crystalline PET, but with lower stiffness and temperature resistance. For precision mechanical parts, acetal is usually the first choice. For food contact, transparency, or chemical resistance to specific media, PET is often specified.

Milling up to 650 × 550 × 450mm. Turning up to 600mm diameter and 1,500mm length. PET is available in a range of plate and rod sizes, though very large sections may be limited by stock availability. Because PET is notch-sensitive and prone to stress cracking, large parts benefit from stress-relief annealing and careful fixture design to avoid point loading during machining.

Material test reports with grade identification and lot traceability. Dimensional inspection reports. Certificates of conformance. For food contact applications, FDA and EU food contact compliance certificates are provided where applicable. For electrical applications, dielectric strength data is available on request. If stress-relief annealing is performed, the heat treatment record is included.