HDPE, acetal and nylon bars and rods are widely used for machined components, wear parts, guides, bushes, rollers, pads and general workshop fabrication. They are not interchangeable. The right material depends on the load, friction, moisture, machining tolerance, temperature and chemical exposure required by the finished part.
Choosing the material before ordering stock can reduce machining problems, premature wear and incorrect fits. Start with the job the component must perform, then compare the properties of HDPE, acetal and nylon against the working conditions.
HDPE, acetal or nylon: the main differences
HDPE for chemical resistance and impact use
High-density polyethylene, commonly shortened to HDPE, is a practical material where moisture resistance, chemical resistance and impact performance are useful. It has a low-friction surface and does not absorb water in the way nylon can, making it suitable for wet areas, washdown environments, liners, chutes and protective components.
HDPE is comparatively soft and has a higher thermal expansion rate than acetal. It is therefore less suited to parts requiring tight dimensional control, highly loaded bearings or fine threads. It can produce stringy swarf when machined, so sharp tools and sensible cutting conditions are important. For straightforward spacers, guards, tank fittings and slide surfaces, HDPE can be a cost-effective option.
Acetal for accurate machined components
Acetal, also known as POM, is often selected where stiffness, wear resistance and dimensional stability are more important. It machines cleanly and is commonly used for gears, bushes, rollers, insulators, valve parts, jigs and fixtures. Its low moisture absorption helps it hold its dimensions more consistently than nylon in changing workshop conditions.
Acetal can be a good choice for close-fitting components, but it is not suitable for every chemical environment. Strong acids, highly oxidising chemicals and some aggressive cleaning fluids can damage the material. Check the grade and chemical compatibility before using it in process equipment or continuous immersion.
Nylon for wear, bearing and load applications
Nylon is a proven engineering plastic for parts exposed to sliding contact, abrasion and repeated loading. Nylon bars and rods are frequently machined into bearings, wear strips, pulleys, wheels, gears and impact-resistant machine parts. The material offers good toughness and can perform well where a part needs to absorb shock rather than remain completely rigid.
The main consideration is moisture absorption. Nylon can take up moisture from its surroundings, which may alter dimensions and mechanical behaviour. This may not be a problem for general-purpose wear pads or bushes, but it matters for close-fitting parts and components used in damp or variable conditions. Where dimensional consistency is the priority, acetal may be the better option.
How to choose the right stock size
Engineering plastics can be supplied as round rods, flat bars, sheets or cut lengths. For a round component, confirm the required finished diameter and length, then allow enough material for facing, turning, workholding and test cuts. Buying stock at the exact finished size leaves little or no allowance for saw marks, ovality or final machining.
For a bored component such as a bush, consider the wall thickness after machining. Very thin walls can flex under load or distort during clamping. If the part will carry a shaft, assess the fit, rotation speed and operating temperature rather than choosing the wall thickness by appearance alone.
For repeat production, compare the bar length with the finished-part dimensions and calculate likely waste. For one-off repairs, a manageable cut length may be easier to handle and can reduce unnecessary material waste.
Machining HDPE, acetal and nylon
All three materials can be machined with conventional workshop equipment, but their behaviour differs from metal. Keep cutting tools sharp, support long workpieces correctly and avoid excessive heat. Heat can soften the material, affect surface finish and allow the part to move during machining.
Acetal generally produces a clean finish and is well suited to turning and milling. HDPE needs care to prevent material dragging or melting at the cut. Nylon can machine well, although its flexibility and moisture-related movement should be allowed for where close tolerances are required.
When drilling deeper holes, withdraw the drill regularly to clear swarf and reduce heat build-up. For close fits, consider drilling undersize and finishing with a reamer or boring operation. Trial machining is sensible when producing precision parts or when the material has been stored in changing environmental conditions.
Threading plastics also needs judgement. Coarse threads are usually more reliable than fine threads, particularly in softer HDPE. For repeatedly assembled parts or high clamp loads, consider threaded inserts, through-bolts, washers or a change in component design.
Consider the finished application
Material selection should reflect the completed component rather than the stock price alone. A low-load packing piece has different requirements from a close-tolerance bearing bush, a conveyor guide or a wear strip under repeated movement.
- Load and movement: check whether the part will carry a load, slide, rotate, flex or absorb impact.
- Moisture: consider washdown, humidity and dimensional changes caused by water absorption.
- Temperature: assess heat from the environment, friction, nearby machinery and the machining process.
- Chemicals: check exposure to oils, fuels, cleaning fluids, acids and other process chemicals.
- Tolerance: allow for machining movement and choose a material that can maintain the required fit.
- Surface contact: consider friction, wear, noise and whether the part will run against metal or another plastic.
Comparing engineering plastics with metal
Metal remains necessary for high loads, high temperatures and demanding structural applications. Steel, stainless steel, aluminium or bronze may be more appropriate where creep, heat or concentrated load would limit an engineering plastic.
Engineering plastics can still provide useful benefits alongside metal. An acetal bush, HDPE liner or nylon wear pad can reduce noise, protect a mating surface and simplify replacement. The correct choice depends on the complete joint or assembly, not just the material used for one component.
Buying checklist for workshop and maintenance work
Before ordering bar or rod stock, confirm the following details:
- material grade: HDPE, acetal/POM or nylon;
- stock form: round rod, flat bar, sheet or cut length;
- required diameter, width, thickness and length;
- machining allowance and finished tolerances;
- operating load, speed, temperature, moisture and chemical contact;
- colour or grade requirements for the finished component;
- compatibility with the mating parts and intended method of installation.
For production work, machine a first-off part before committing to a full batch. Check bore size, outside diameter, surface finish and movement under the expected load. For a replacement component, measure both the mating part and the worn item where possible, because wear can hide the original dimensions.
HDPE, acetal and nylon FAQs
Is HDPE interchangeable with acetal or nylon?
No. HDPE, acetal and nylon have different levels of stiffness, wear resistance, moisture absorption, thermal movement and chemical resistance. Select the material for the actual working conditions.
Which material is best for a close-fitting bush?
Acetal is often considered where dimensional stability and clean machining are important, but the correct choice also depends on load, speed, temperature, lubrication and the mating shaft.
Which material is suitable for wet environments?
HDPE has very low water absorption and is often considered for wet or washdown environments. Nylon can absorb moisture, while acetal may offer better dimensional stability than nylon. Always check the complete application.