Machining Acetal Copolymer — Speeds, Feeds & CNC Tips (POM-C)

Acetal copolymer (POM-C, Celcon, Hostaform) machines with essentially the same ease and parameters as acetal homopolymer (Delrin). Both are semicrystalline POM materials that cut cleanly, hold tight tolerances, and produce short chips with carbide tooling. The practical differences are minor — POM-C has a slightly lower melting point (165°C vs. 175°C for POM-H) and can produce slightly longer chips in some turning geometries — but neither difference requires changing your machining strategy. This guide covers the complete workflow for machining acetal copolymer from stock rod, sheet, and tube.

At a glance:

• Target keyword: "machining acetal" — vol 100, CPC $4.00 — high commercial intent
• POM-C machines the same as Delrin; same speeds, feeds, and tooling apply
• Surface speed (turning): 400–800 SFM for standard (unfilled) grades
• Milling: 300–600 SFM; chip load 0.003–0.006 IPT
• No pre-annealing required for standard operations
• Do NOT laser-cut acetal — waterjet, bandsaw, or router only
• Glass-fiber reinforced POM-C grades (Hostaform C 52021): reduce SFM 30–50%, use PCD inserts

Acetal Copolymer vs. Delrin: Machining Differences

The two materials are nearly identical to machine. Three minor differences:

1. Melting point: POM-C melts at 165°C vs. 175°C for POM-H. In aggressive cutting conditions (very high SFM, low feed rates that cause rubbing), POM-C surfaces may show slight glazing or smearing sooner. Keep feed rates above 0.004 IPR in turning; continuous chip is critical.

2. Chip character: Some POM-C formulations (particularly Hostaform and certain Celcon grades) produce slightly longer, more stringy chips than Delrin 150. In production turning, use a chip breaker geometry insert or increase the tool nose radius slightly to encourage chip curl.

3. Hot-water resistant grades: Heat-stabilized POM-C grades (Celcon HS, Hostaform C 9021 HS) may machine with slightly higher cutting force due to the thermal stabilizer package modifying polymer morphology. Reduce SFM by 10–15% if surface glazing appears on these grades.

Otherwise: if your shop has established parameters for Delrin, use them for acetal copolymer. See the Delrin machining guide for the parallel reference.

Turning Parameters

Recommended Speeds and Feeds (CNC Lathe)

Tooling for Turning

Standard POM-C grades: Sharp, positive-rake uncoated carbide (C-2) inserts. High-speed steel acceptable for short runs. Keep tools sharp; dull inserts increase heat and lead to glazed surfaces in POM-C sooner than in POM-H.

Glass-fiber reinforced POM-C: TiAlN-coated carbide or PCD inserts. Same tooling upgrade required as Delrin 570.

Tips:

• Continuous chip is critical in POM-C: do not dwell, do not interrupt the feed mid-cut
• Support slender parts (L/D > 6) with steady rest or live center — POM-C is slightly more flexible than POM-H at equivalent cross-sections due to lower modulus
• Coolant optional for standard grades; helpful for deep cuts and thin walls; required for glass-filled grades in production

Milling Parameters

End Mill Selection

2–3 flute end mills with helix angle 30–40°; sharp edges; uncoated carbide for standard grades; TiAlN or PCD for glass-filled grades.

Milling tips:

• Climb milling gives slightly better surface finish than conventional milling in POM-C
• Compressed air chip clearing for pockets and slots >3× tool diameter
• Thin sections (<0.060"): reduce chip load by 50%; take multiple light passes
• For glass-filled POM-C: use dust extraction; glass fiber is a respiratory irritant

Drilling

Acetal copolymer drills cleanly. Chip evacuation is the main concern in deep holes.

Drilling tips:

• Center drill first to prevent walking on entry
• Peck cycle every 0.5–1× diameter in deep holes
• Drill 0.005–0.010" undersize; ream to final tolerance for precision bores
• Coolant or air blast improves hole quality in deep bores

Tolerances After Drilling and Reaming

Tapping and Threading

Acetal copolymer threads well using the same guidelines as Delrin:

• Spiral-flute taps for blind holes; spiral-point for through holes
• Drill to 70–75% thread engagement
• Light tapping fluid recommended; dry tapping acceptable for coarse threads in standard POM-C
• For glass-filled POM-C: use carbide or premium coated HSS taps; monitor wear closely
• Thread inserts (Heli-Coil, E-Z Lok) extend life in repetitive assembly/disassembly applications

Sheet Fabrication

Bandsaw

Bi-metal blades, 6–10 TPI for standard sheet thicknesses. Feed control is important — avoid forcing the blade, which builds heat at the cut face.

CNC Router

O-flute (single-flute) or 2-flute upcut carbide. SFM 400–700; chip load 0.003–0.006 IPT. Vacuum table or clamp workholding. This is the most efficient method for complex 2D profiles in acetal copolymer sheet.

Waterjet Cutting

Preferred for large-sheet blanking and complex profiles. No heat-affected zone. Tolerances: ±0.010–0.015" standard; ±0.005" precision waterjet. Both POM-C and POM-H can be waterjet cut without concerns about chemical emissions.

Laser Cutting — DO NOT USE

Laser cutting generates formaldehyde gas from any polyoxymethylene (POM), including acetal copolymer. This is an occupational health hazard regardless of whether you are cutting POM-H or POM-C. Use waterjet, bandsaw, or router.

Surface Finish Achievable in Acetal Copolymer

Special Considerations for Large-Diameter Acetal Copolymer Rod

A key advantage of acetal copolymer over Delrin in machining is the absence of centerline porosity in large-diameter rod. When turning flanges, pulleys, and thick discs from rod stock 4" and above, acetal copolymer rod can be machined through the full cross-section without encountering a voided or porous core zone. The toolpath for boring or facing the center of large POM-C rod proceeds identically to any other solid stock. This is not the case with Delrin (POM-H) rod above ~3" diameter. See acetal copolymer specifications for the full discussion.

More related guides

Compare to other materials

• Machining Delrin (POM-H)
• Machining PEEK
• Delrin vs. Acetal Copolymer

Applications

• Acetal Copolymer Applications
• Bushings and Bearings in Acetal

Frequently asked questions — Acetal Copolymer FAQ