Delrin Machining
POM-C and POM-H acetal parts with tight tolerances, low moisture absorption and clean finishes — from single prototypes to repeat production.
The Plastic That Machines Like Brass
Delrin — the DuPont trade name for acetal (POM) — is the easiest engineering plastic to machine, and the most predictable. It cuts crisp, holds tolerance, barely absorbs water, and delivers an excellent combination of stiffness, low friction, and fatigue resistance. If your design calls for a precision plastic part that actually stays the size we machined it, Delrin is usually the answer. IsoCNC runs Delrin and acetal machining daily for North American and European OEMs, from single prototypes to repeat production.
POM-C vs POM-H: Which Acetal You Need
- POM-H (Delrin / homopolymer) — the original Delrin. Slightly higher strength, stiffness, and wear resistance than copolymer. Best for gears, bearings, and load-bearing mechanical parts. Downside: centerline porosity in larger rod and plate, so avoid thick sections with critical bores
- POM-C (acetal copolymer) — more chemically resistant (especially to hot water and alkalis), no centerline porosity, and slightly better dimensional stability. The right choice for thick sections, food-contact parts, and parts exposed to cleaning chemicals
- Filled grades — glass-filled acetal for extra stiffness, PTFE-filled (e.g. Delrin AF) for low-friction bearings and wear pads
Not sure which one your drawing needs? Tell us the environment and loads — for most mechanical parts POM-H is the default, and for thick or wet-environment parts we recommend POM-C. Either way, POM machining runs on the same tooling and cycle times, so the grade choice rarely moves the price.
Machinability and How We Cut It
Delrin's machinability is the benchmark other plastics are judged against. Our approach on the shop floor:
- Sharp tools, fast cuts — carbide tooling at high speeds with high feed rates; Delrin chips cleanly and does not gum up cutters
- Burr control — the one real nuisance. Delrin throws stringy burrs on edges and cross-holes, so we program climb milling, chamfer passes, and sharp tool changes, then hand-deburr critical edges as standard
- Heat management — acetal softens around 230°F (110°C). Air blast or light coolant keeps thin features from melting and gumming
- Low moisture absorption — at roughly 0.2% water absorption, Delrin holds size through machining and in service far better than nylon. No conditioning cycles needed before final passes
Delrin vs. Nylon and Other Plastics
Buyers often land on this page deciding between Delrin and nylon. The short version: nylon is tougher and cheaper in thick sections, but it absorbs water and grows — a nylon bushing machined to size can bind after a humid month in service. Delrin costs a little more and holds its dimensions. For tighter-tolerance, drier-environment, or wear-critical parts, Delrin wins; for impact-resistant structural parts where a few thousandths of growth does not matter, nylon is fine. For higher temperatures or medical requirements, see PEEK machining; for the full plastics range, see plastic CNC machining.
Tolerances and Surface Finishes
Delrin holds the tightest tolerances of any common engineering plastic. General features machine to ±0.005 in (±0.13 mm); critical bores, bearing fits, and gear features to ±0.002 in (±0.05 mm) quoted against the drawing. As-machined finish is Ra 3.2 µm (125 µin) standard, to Ra 0.8 µm (32 µin) on bearing and sealing surfaces — and Delrin's naturally slick surface often performs well below the measured Ra.
Delrin machined parts are almost always used as-machined; the material does not accept plating or anodizing, and rarely needs coating. Laser marking works well for part numbers and logos. See surface finishes for plastics options.
Typical Delrin Parts
Gears, sprockets, bushings, bearings, rollers, wear pads, guides, cams, valve components, electrical insulators, fixtures, and conveyor components. Most Delrin work runs on CNC turning and 3-axis milling; it's also an excellent fixture material — we machine our own soft jaws from it.
Delrin Machining — Capability Summary
| Capability | Specification |
|---|---|
| Grades in stock | POM-H (Delrin homopolymer), POM-C copolymer, PTFE-filled, glass-filled |
| General tolerance | ±0.005 in (±0.13 mm); precision features to ±0.002 in (±0.05 mm) |
| Moisture absorption | ~0.2% — excellent dimensional stability, no pre-conditioning needed |
| As-machined finish | Ra 3.2 µm (125 µin); to Ra 0.8 µm (32 µin) on request |
| Finishes | As-machined, bead blast (matte), laser marking |
| Batch range | 1 pc prototype to repeat production volumes |
| Typical lead time | Prototypes from 3 days; production typically 2–3 weeks |
Drawing Tips for Delrin Parts
- Specify POM-H or POM-C if it matters — or note the environment (hot water, chemicals, food contact) and let us pick. “Acetal” alone gets quoted as POM-H.
- Avoid thick critical bores in POM-H — centerline porosity in large rod can show up inside a bored hole. Use POM-C, or let us bore from solid plate.
- Chamfer your edges on the drawing. A small chamfer callout is cheaper than a deburr-to-sharp-edge argument at inspection, and on Delrin it also improves handling safety.
- Tolerance bearing fits against the mating part, not a habit. Delrin runs well at close clearances, but press fits in plastic creep over time — tell us the shaft size and we will recommend the fit.
Quote Your Delrin Parts
Send STEP files and drawings — we'll come back with pricing, lead time, and DFM feedback within 1–2 business days. For other plastics and metals, see the full materials page.
Quote Your Delrin Parts
Send STEP files and drawings — we'll come back with pricing, lead time, and DFM feedback within 1–2 business days.
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