Engineering plastics are lighter than metal, often self-lubricating, electrically insulating, and resistant to many chemicals. For bushes, guides, wear strips, insulators, and low-volume parts, a machined plastic part can be a better and cheaper choice than metal. Moulding only makes sense at high volumes; for prototypes and small batches, machining is the practical route.
Delrin (acetal, POM)
Acetal is stiff, strong, dimensionally stable, and has low friction. It is one of the easiest plastics to machine to tight tolerances, which makes it a favourite for precision plastic parts.
- Good for: gears, bushes, rollers, cams, valve parts, and precision spacers.
- Watch for: poor resistance to strong acids, and it is hard to bond with adhesives.
Nylon (polyamide)
Nylon is tough, wear resistant, and absorbs shock well. It is widely used for wear pads, sheaves, and bushings. Its main drawback is moisture absorption: nylon swells slightly in humid conditions, so it is less suited to parts that must hold very tight tolerances.
PTFE (Teflon)
PTFE has outstanding chemical resistance, a very low coefficient of friction, and a wide working temperature range. It is also soft and prone to creep under sustained load, which makes holding tight tolerances harder.
- Good for: seals, gaskets, chemical-handling parts, insulators, and low-friction slides.
- Watch for: deformation under load; design with generous wall thicknesses.
UHMW polyethylene
Ultra-high-molecular-weight polyethylene is extremely tough, very slippery, and has excellent abrasion resistance at a modest price. It is common in conveyors and material-handling equipment.
- Good for: wear strips, chain guides, star wheels, and chute liners.
- Watch for: high thermal expansion and low stiffness; it is not suited to precision parts or high temperatures.
Polycarbonate
Polycarbonate is tough, impact resistant, and transparent, which makes it ideal for guards, covers, sight windows, and enclosures. Machined edges and faces can be polished when clarity matters.
Designing machined plastic parts
- Allow for thermal expansion: plastics expand far more than metals as temperature changes.
- Avoid very thin walls, which can flex under clamping and cutting forces.
- Specify tolerances realistically; plastics move more than metals with temperature and humidity.
- Use threaded inserts for screw threads that will be assembled and disassembled often.
Quick comparison
- Precision and stiffness: Delrin / acetal
- Toughness and wear: nylon
- Chemicals and lowest friction: PTFE
- Abrasion resistance on a budget: UHMW
- Transparency and impact strength: polycarbonate
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Related services: Custom Parts Manufacturing · Prototype Machining
