Delrin (Acetal/POM) CNC Machining Guide

Delrin — DuPont's trade name for homopolymer acetal (polyoxymethylene, POM-H) — is one of the most reliable engineering plastics on a CNC machine. It cuts cleanly, holds tolerance well, and produces a finish close to that of soft metals. Olympus Machining is a U.S.-based, ITAR-registered precision CNC machining shop in Hanover, Pennsylvania producing Delrin and Acetal components for OEMs nationwide.

What Is Delrin?

Delrin is a semi-crystalline thermoplastic produced by polymerizing formaldehyde. There are two common families: homopolymer (Delrin / POM-H) and copolymer (Acetal / POM-C). Homopolymer is stiffer and has higher tensile strength; copolymer is more dimensionally stable in long-term hot or wet service and machines with slightly less center-line porosity. Both are widely specified as a metal replacement where weight, corrosion resistance, and low-friction wear matter more than peak temperature performance.

Tensile strength: ~70 MPa (10 ksi) for Delrin 150; ~60 MPa for copolymer Acetal.
Continuous service temperature: ~180°F (82°C); short-term excursions to ~250°F.
Density: ~1.42 g/cm³ — roughly one-fifth the weight of steel.
Coefficient of friction: ~0.2 against steel, dry — excellent for bearings and gears.
Water absorption: ~0.2% over 24 hours — among the lowest of engineering plastics.

Machining Approach

Delrin machines a lot like brass: free-cutting, low cutting forces, long stringy chips. Olympus Machining runs Delrin with sharp, polished carbide tooling and positive rake geometries to keep chips evacuating and avoid heat build-up at the cutting edge. Coolant is optional for most milling operations — air blast is usually enough — but flood coolant helps on deep turning and long bar work to keep the part dimensionally stable.

The biggest production risk is stress-induced distortion in thick stock. Rod and plate over ~2″ section can hold residual stress from extrusion or molding; we rough such parts oversize, allow them to stabilize, then take light finishing passes for final dimensions on tolerance-critical features.

Typical Tolerances & Finish

±0.002″ on milled features, ±0.001″ on precision turned features as standard.
Tighter tolerances are achievable on small, thin parts; thermal expansion (~10× that of steel) drives the limit on larger envelopes.
Ra 0.8 µm achievable as-machined; polished or burnished finishes available on request.
Certificates of Conformance and material traceability with every shipment.

Typical Applications

Industrial / Motion

Bushings, sleeve bearings, cams, gears, wear strips, conveyor guides, sliding components.

Fluid Handling

Pump manifolds, valve bodies, fittings, and bodies for low-pressure liquid handling.

Electrical / Fixturing

Insulators, test fixtures, machine guards, and tooling components where metal would gall or arc.

Delrin vs. Other Engineering Plastics

Delrin vs. Nylon (PA6/PA66): Delrin holds tighter tolerance because nylon absorbs water and grows by up to 2–3%. Choose Delrin where dimensional stability matters; choose nylon where impact toughness leads.
Delrin vs. UHMW-PE: UHMW has lower friction and better wear in abrasive sliding; Delrin is stiffer and machines to a finer tolerance.
Delrin vs. PEEK: PEEK serves continuously above 480°F and is chemically inert; Delrin is roughly an order of magnitude less expensive and far easier to machine.

Need Delrin Parts Quoted?

Send a drawing or STEP file with the grade specified (Delrin 150, Delrin 100, Acetal copolymer) and tolerance schedule. A CAM engineer reviews every quote.

Submit a Drawing

Last reviewed: May 12, 2026