Why Delrin / Acetal for CNC Machined Plastic Parts?
Delrin (DuPont's brand for acetal homopolymer, also called POM-H) and the closely related Acetal copolymer (POM-C, Celcon) are the most widely machined engineering plastics. They combine exceptional stiffness for a thermoplastic with very low friction, good wear resistance, dimensional stability in moisture, and clean machinability. For gears, bearings, bushings, guide rails, valve components and precision structural parts that need to replace metal at lower weight and cost, Delrin is the first plastic to consider.
Delrin / Acetal Grades We Machine
| Grade | Key characteristic | Best for |
|---|---|---|
| Delrin 150 / 500 (POM-H) | Homopolymer — highest strength and stiffness | Gears, precision parts, heavily loaded bearings |
| Acetal Copolymer (POM-C) | Better chemical resistance, no centre porosity | Chemical processing parts, large-diameter rod stock (no centre void) |
| Glass-Filled Acetal (GF-Acetal) | Higher stiffness and heat resistance | Structural load-bearing parts at elevated temperatures |
| UV-stabilised / colour acetal | Added UV resistance or colour match | Outdoor parts, colour-coded components |
Mechanical Properties (Delrin 150 Homopolymer)
| Property | Typical value |
|---|---|
| Tensile strength | ~68 MPa |
| Flexural modulus | ~3.1 GPa |
| Impact strength (notched) | ~75 J/m |
| Hardness | ~120 HRR (Rockwell R) |
| Density | 1.42 g/cm³ |
| Max service temperature | ~90–105 °C continuous |
| Water absorption (24h) | ~0.25% |
| Friction coefficient (dry) | ~0.20–0.35 (vs steel) |
| Machinability | Excellent — cuts like aluminium |
How We Machine Delrin / Acetal
Delrin machines very cleanly at high speeds with sharp tooling — in many respects it machines faster than aluminium. Key points for quality plastic CNC parts:
- Tolerances: ±0.025 mm on critical features is achievable; moisture and temperature cause minor dimensional shift — we account for this in the machining strategy.
- Tooling: Sharp uncoated or TiN carbide; high speeds and moderate feeds produce clean cuts and low heat build-up.
- Heat management: Acetal melts at ~175 °C — tool friction must be minimised. We use air coolant or light mist; flood coolant is generally not needed.
- Support: Thin walls require support to prevent deflection — we design fixtures around part geometry.
- Centre porosity: Large Delrin rod can have a porous centre; for large-diameter parts we use acetal copolymer (POM-C) which does not have this issue.
Typical Delrin / Acetal CNC Parts
- Gears and sprockets — low-noise, self-lubricating, suitable for light-to-medium loads
- Bushings and plain bearings — low friction, no external lubrication needed
- Guide rollers and slide blocks — conveyor and linear motion applications
- Valve and pneumatic components — valve seats, spools, manifold bodies
- Electrical insulators — switch components, PCB standoffs
- Food processing parts — FDA-compliant grades available (natural white acetal)
- Prototype and replacement parts — fast-turn plastic prototypes; replacement plastic parts from worn samples
Replacing metal bearings with Delrin? Delrin/acetal bushings are a common metal-replacement in light-to-medium load bearing applications — they reduce weight, eliminate lubrication requirements, reduce noise and often last longer in clean environments. Tell us the load, speed and environment and we'll confirm suitability.
Frequently Asked Questions
What is the difference between Delrin (POM-H) and Acetal Copolymer (POM-C)?
Delrin is DuPont's brand for acetal homopolymer (POM-H) — it has slightly higher tensile and flexural properties. Acetal copolymer (POM-C, Celcon) has better chemical resistance and, critically, does not develop the centre porosity found in large-diameter Delrin rod — making it the choice for parts machined from large rod stock. For most machined gears, bushings and structural parts, either works well and we select based on availability and your specific requirements.
What tolerances can you achieve on Delrin CNC parts?
±0.025 mm is routinely achievable for critical features. Be aware that acetal absorbs a small amount of moisture (0.25% after 24h immersion) and undergoes minor thermal expansion — for parts with very tight dimensional requirements in wet environments, discuss this with us at quoting so we can account for service conditions in the machining tolerances.
Is natural white acetal food-safe?
Natural (white/off-white) acetal copolymer meets FDA 21 CFR and EU 10/2011 requirements for food contact in most grades. We supply FDA-compliant acetal copolymer rod for food processing parts on request. Black acetal may contain pigments that are not food-safe — specify natural white if food contact is required.
Can you machine Delrin parts from a drawing or photo?
Yes — we accept all starting points: CAD files (STEP/IGES/DXF), technical drawings, photos with dimensions, or physical samples. Delrin parts from a sample is straightforward: we measure the sample, reconstruct the geometry if needed, and machine the reproduction. Lead times are fast since Delrin machines quickly.
What other engineering plastics do you machine besides Delrin?
We regularly machine nylon (PA6, PA66, PA12), PTFE/Teflon, PEEK, polycarbonate (PC), UHMW-PE, HDPE, ABS, PVC and various filled grades. Nylon and PEEK are the other most common precision engineering plastics we produce; PTFE is used where chemical resistance or low friction is critical at higher temperatures. Let us know your requirements and we recommend the right grade.
Get a Delrin / Acetal Quote
Sketch, photo or CAD accepted. Reply in 24h.