PL · engineering plastic
Acetal Copolymer POM-C (Delrin equivalent)
The best-machining plastic in this catalogue: it produces clean chips, holds a tolerance without drama and takes a fine finish. If a plastic part needs to be dimensionally right, this is usually the material.
Quoting this material
- Typical lead time
- 7–12 working days
- Condition
- Extruded or moulded stock
- Achievable finish
- Ra 0.8 µm typical · Ra 0.2 µm best
Machined in-house to your drawing: see the precision CNC machining service and the machine and inspection capability it runs on.
Machinability
Our own 1–10 shop ranking, not a published index: 10 is free-cutting brass C360, 1 is Inconel 718. It ranks how a material behaves on the floor - cycle time, chip control and tool life together. Where a published index exists it is quoted in the note.
The best-machining plastic in this catalogue: it produces clean chips, holds a tolerance without drama and takes a fine finish. If a plastic part needs to be dimensionally right, this is usually the material.
Properties as supplied
| Parameter | Value | Unit |
|---|---|---|
| Tensile strength | 68 | MPa |
| Modulus of elasticity | 2.9 | GPa |
| Hardness | 84 | Shore D |
| Continuous service temperature | 100 | °C |
| Thermal conductivity | 0.31 | W/m·K |
| Density | 1.41 | g/cm³ |
Hardness, tensile and thermal figures are typical published values for the condition stated. Actual mill certificates govern; send the specification with the drawing and we confirm against the certificate before the material is cut.
Condition
Extruded or moulded stock
Heat treatment
No heat treatment required for most parts, though stress-relieving is used on a heavily machined part where stability is critical. It absorbs very little moisture, so it does not need the drying that nylon does.
Achievable surface finish
Ra 0.8 µm
Ra 0.2 µm
The best as-machined plastic finish of the common grades, and it stays dimensionally where it was machined.
Tooling and cutting parameters
Cutting speed
- 200–500 m/min (sharp uncoated carbide)
Feed
- 0.10–0.40 mm/rev turning · 0.10–0.35 mm/tooth milling
Tooling
- Uncoated polished carbide, sharp positive rake, generous relief
Coolant
- Compressed air; mist for deep pockets
Starting points for carbide on a rigid setup, not a guarantee. The right numbers depend on the machine, the toolholder and the fixturing - ask and we will say what we would actually run.
Typical applications
- Gears, cams and bushings
- Precision mechanical components
- Food handling and conveyor parts
- Pump and valve internals
- Insulators and spacers
DFM notes for this grade
- Service temperature is the limit: POM is excellent to about 100 °C and loses stiffness quickly above it - do not specify it in a hot enclosure
- It is not suitable for strong acids or oxidising chemicals, however good it looks mechanically
- Clamping pressure distorts the part: use soft jaws or a vacuum fixture and light pressure, and hold the part on a machined face rather than a sawn one
Questions buyers ask
- Why is POM so much better to machine than other plastics?
- It is hard, stiff and dimensionally stable, and it forms a real chip instead of smearing. Nylon absorbs moisture and moves, PTFE is soft and creeps, polyethylene cannot hold a tolerance - POM just behaves like a slightly soft metal.
- Can POM hold a press fit?
- Yes, with a much larger interference than metal because the modulus is low: roughly 0.1–0.2 mm on a 20 mm diameter is typical. POM is also used for snap fits and living hinges, so the design can rely on elastic deflection rather than on friction.
Grades we would quote instead
PEEK
5/10Machines cleanly for a plastic but it holds heat at the cut and the swarf will not break.
Nylon 6/6 (PA66)
6/10Machines well when dry, but it absorbs moisture from the air and grows - which is the opposite of what most machined parts are expected to do.
UHMW-PE
6/10Cuts easily but badly: it is soft, it moves under clamping and it produces a continuous string of swarf that has to be managed.