CNC Materials

POM / Acetal (Delrin) Machining Guide

POM (polyoxymethylene), sold as acetal or under the Delrin brand, is one of the most machinable engineering plastics and a default choice for precision gears, bushings, bearings and low-friction wear parts. It combines high stiffness, excellent dimensional stability and very low moisture absorption, which is exactly why it holds tight tolerances on a lathe or mill. This guide covers the two grades, the properties that matter on the shop floor, how POM compares with other plastics we machine, and the design points that keep parts in tolerance after cutting. Davantech machines POM to print as part of our CNC machining services; see the full list of CNC materials for alternatives.

POM Acetal cnc machining
POM at a glance
Material: Polyoxymethylene (acetal)
Grades: Homopolymer (Delrin), copolymer
Density: ~1.41 g/cm³
Moisture uptake: ~0.2% (very low)
Service temp: -40 to ~100 °C
Machinability: Excellent
Typical tolerance: ±0.025 mm achievable
Best for: Gears, bushings, wear parts
Reference data

POM key properties

Typical values for machining-grade acetal. Use them for material selection, not as certified design minimums;
exact figures depend on grade and supplier, and we provide mill or material certificates on request.

Property Typical value What it means for your part
Density 1.41 g/cm³ Heavier than nylon or PP; lighter than PTFE
Tensile strength 60–70 MPa Strong and stiff for an unfilled plastic
Moisture absorption ~0.2% Parts stay dimensionally stable in humid or wet use
Coeff. of thermal expansion ~110 µm/m·K High; allow for growth on large or close-fit parts
Max continuous service temp ~100 °C Short excursions higher; not for hot-water or steam
Coeff. of friction 0.2–0.35 Low, self-lubricating; ideal for gears and bushings
Chemical resistance Good Resists fuels, solvents; attacked by strong acids
UV resistance Poor Use UV-stabilised (black) grade for outdoor parts

Note: POM is flammable and gives off formaldehyde if overheated, so keep tooling sharp and cutting temperatures down. It cannot be solvent-bonded easily; design for mechanical fasteners or assembly instead of gluing.

Choosing a grade

Homopolymer vs copolymer

Delrin (homopolymer) is slightly stronger and stiffer and takes a finer finish, which suits small precision gears
and high-load bushings. Copolymer acetal resists hot water and strong chemicals better and has no risk of the
centreline porosity that can appear in thick homopolymer sections. For most parts either works; the decision is
driven by section thickness, chemical exposure and load.

Grade Strength & stiffness Chemical / hot-water resistance Thick-section porosity
Homopolymer (Delrin) Highest Good Possible centreline porosity
Copolymer Very good Better None

POM vs other plastics we machine

How acetal compares with the other engineering plastics in our material range, so you can choose the right one before you send a drawing.

Property POM / Acetal PA66 Nylon PVDF ABS
Moisture absorption ~0.2% High (to ~8%) <0.04% 0.3–0.9%
Max service temp ~100 °C ~100–120 °C ~150 °C ~80 °C
Wear / friction Excellent Good Moderate Poor
Chemical resistance Good Moderate Excellent Moderate
Machinability Excellent Good (gummy) Good Good
Relative cost Low–mid Low–mid High Low

Related guides: Machining PA66 / nylon  ·  PVDF  ·  all CNC materials

On the machine

Machining characteristics

  • Machines like brassPOM cuts cleanly with sharp tools at high speed, breaks chips well and takes a fine finish without coolant, so it is fast and cheap to machine to tight tolerances.
  • Watch thermal expansionIts expansion coefficient is roughly ten times that of steel. On large or close-fit parts, cutting heat and ambient temperature shift dimensions, so we let parts stabilise before final measurement.
  • Internal stress can move partsExtruded stock carries internal stress. Removing a lot of material unevenly can warp thin parts; rough-then-finish passes, and annealing where needed, keep them flat and true.
  • Excellent thread and gear detailAcetal holds fine threads, small module gear teeth and crisp edges, which is why it is a first choice for precision motion parts.
Where it is used

Typical applications

Motion parts
  • Spur, helical and worm gears
  • Bushings and plain bearings
  • Cams, rollers and guides
Fluid handling
  • Manifolds and fittings
  • Valve components
  • Pump parts
Mechanical / electrical
  • Insulators and housings
  • Snap-fit and clip parts
  • Wear pads and slides
Need POM parts machined to print?
Send your drawing or STEP file. We machine acetal to tight tolerances and provide material certificates on request.

Get a quote

Related pages
CNC Machining ServicesOur full milling, turning and EDM capability CNC MaterialsEvery metal and plastic we machine Machining PA66 / NylonThe nylon alternative to acetal
FAQ

POM machining questions

Is Delrin the same as POM or acetal?
Delrin is DuPont’s brand name for homopolymer POM. “Acetal” and “POM” are the generic names and cover both homopolymer and copolymer grades. When a drawing calls out Delrin specifically we machine homopolymer; otherwise we advise on the grade that best fits the application.
What tolerance can you hold on POM parts?
Acetal machines very well and we routinely hold ±0.025 mm on typical features. Because POM has a high thermal expansion coefficient and can carry internal stress, we let parts stabilise and, where needed, anneal stock before finishing to keep close tolerances stable. See our tolerances guide for detail.
Should I choose POM or nylon (PA66)?
Choose POM for dimensional stability, low friction and wear, especially in wet or humid conditions where nylon absorbs moisture and swells. Choose PA66 where you need higher impact toughness or better resistance to certain chemicals. The comparison table above summarises the trade-offs.
Can POM be used outdoors?
Only in a UV-stabilised grade. Natural acetal has poor UV resistance and will chalk and embrittle in sunlight. Black, UV-stabilised POM is suitable for many outdoor parts; tell us the environment and we will specify the right grade.
Can POM parts be glued or welded?
POM has a low-surface-energy, chemically resistant surface, so it does not solvent-bond well and is difficult to glue reliably. Design for mechanical fasteners, press-fits or snap-fits instead. We can handle these in assembly as part of a finished sub-assembly.