POM vs Nylon for Automation Fixtures
Contents
- The Short Answer
- Dimensional Stability and Moisture
- Friction, Wear and Marking
- Machining Behaviour
- When PEEK Is the Right Answer
- A Practical Selection Guide
Which engineering plastic to choose for product nests, guides and wear components — a direct technical comparison.
The Short Answer
POM (Delrin) is the better default for product nests, guides and locating features that must hold a dimension and slide or contact parts without marking them. Nylon (PA66) is the better choice where impact, shock loading or a part that has to flex is the dominant requirement. Both machine well; the decision usually comes down to dimensional stability versus toughness.
Dimensional Stability and Moisture
Nylon absorbs moisture from the air and grows as a result — a few tenths of a percent, which on a 100 mm nest is enough to matter against a 0.15 mm location tolerance. POM absorbs very little and holds its machined size far better in a shop-floor environment. If a fixture is measured against a tight positional callout, this alone usually decides the material.
Friction, Wear and Marking
POM has a low coefficient of friction and good dry-running behaviour, which suits sliding guides, cam surfaces and nests where parts are pushed in and out repeatedly. Nylon is slightly more abrasive in sliding contact and can be more prone to creep under sustained load, but it resists impact and abuse better — a dropped part or a jammed mechanism is less likely to chip it.
Machining Behaviour
POM machines cleanly with sharp tooling and produces an excellent as-machined surface, which is why it is our default for non-marring contact surfaces. Nylon tends to be gummy and can leave burrs or fuzz on edges; it needs sharp tooling, generous chip clearance and attention to heat build-up. Both materials move after machining if stresses are released unevenly, so keep cuts balanced and avoid heavy climb finishing passes on thin walls.
When PEEK Is the Right Answer
Where the fixture sees elevated temperature, aggressive chemicals or repeated sterilisation, PEEK is the appropriate step up: it holds strength and stiffness at temperatures that would soften POM or nylon, with excellent chemical resistance. It is considerably more expensive, so it is rarely the right choice for general-purpose nests.
A Practical Selection Guide
Product nests, guides, non-marring contact pads and wear strips: POM. Impact-prone guards, covers and parts that must flex: nylon PA66. High temperature, chemical exposure or cleanroom-critical components: PEEK. If the application sits between two materials, we will machine a sample part first and let you test it in the cell before committing to a batch — samples are quoted at single-piece pricing, and there is no minimum quantity.
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