This article is part of the CNC Machining Materials Guide: Metals, Plastics & Superalloys on CNX Precision.
Delrin vs nylon is one of the most common material debates in precision plastic machining. Both are proven engineering thermoplastics used for gears, bushings, rollers, and wear components. Yet they behave differently on the machine and in service. Delrin, an acetal resin also known as POM, combines low moisture absorption with excellent dimensional stability and a naturally low-friction surface. Nylon, the polyamide family, offers greater toughness and impact strength but absorbs moisture and changes size with humidity. This guide compares machinability, moisture effects, wear, and cost, then offers practical guidance for bearings, gears, and sliding parts.
Delrin vs Nylon: The Short Answer
Delrin is the trade name for acetal homopolymer, a semi-crystalline thermoplastic sold under names like POM. It absorbs very little moisture, typically around 0.2 percent, so machined parts hold their dimensions in changing environments. The surface is hard, smooth, and naturally slippery, which is why Delrin is a standard choice for precision gears, bushings, and bearing surfaces. It also resists creep better than many commodity plastics, so loaded parts keep their shape over time. Acetal retains stiffness at low temperatures and resists most solvents, which is why it appears in fuel systems, valves, and consumer hardware.
Nylon covers the polyamide family, most commonly PA 6 and PA 66. It is tougher than acetal and handles higher impact loads and repeated flexing. The tradeoff is moisture. Nylon readily absorbs water from the air, which can change part dimensions, soften the material slightly, and complicate machining. Glass-filled and oil-filled grades adjust these properties, but the hygroscopic nature remains. Put simply, the Delrin vs nylon decision comes down to dimensional stability against toughness.
Machinability and Dimensional Stability
Both materials machine well with sharp, single-point carbide tools and standard speeds for engineering plastics. Delrin is generally the easier of the two. It cuts cleanly, holds a fine surface finish, and resists the fuzzing and melting that can trouble softer plastics. Delrin also chips in small, clean fragments that evacuate easily. Because its moisture uptake is minimal, a part measured on Monday still measures the same on Friday. Tool geometry matters too; generous relief angles and polished flutes keep the plastic from rubbing and heating up.
Nylon machines cleanly when dry, but dimensional control needs more planning. Stock shapes often arrive with internal stresses that relax during cutting, causing movement. Many shops machine rough, then stress-relieve or condition parts before finishing passes. Nylon also produces long, stringy chips that need good evacuation. In any Delrin vs nylon decision where the part carries tight tolerances in a humid environment, acetal usually wins. Drying the stock before cutting also stabilizes dimensions during the operation itself.
Moisture, Friction, and Wear
Understanding moisture is the core of every Delrin vs nylon comparison. The low absorption of Delrin keeps clearances stable in wet or cycling conditions. That stability carries through assembly too, so press fits and snap fits stay predictable. Nylon can absorb several percent of its weight in water at high humidity, and parts swell as a result. That swelling changes bearing clearances and gear backlash, sometimes enough to bind a mechanism. For parts that face washdown or outdoor weather, this single property often settles the decision.
On friction and wear, both perform well but in different ways. Delrin offers a low coefficient of friction against steel and against itself, making it a favorite for sliding and pivoting parts. Nylon is self-lubricating and highly abrasion resistant, and it often outlasts acetal in high-load sliding applications, especially when lubricated. For wear parts that see impact or shock, the toughness of nylon becomes the deciding factor. Chemical resistance is comparable for common oils and fuels, while acetal handles hot water and hydrolysis better than nylon. When two surfaces slide together, pairing nylon against steel or acetal against acetal are both proven approaches.
Cost and Availability
Both materials are commodity engineering plastics, available as rods, plates, and tubes in many sizes. Unfilled nylon typically costs less than acetal, so for large, low-tolerance parts, nylon can reduce material spend. Filled grades shift the picture. Glass-filled nylon adds stiffness, oil-filled grades improve wear, and both cost more than the base resin. Lead times for both materials stay short, and custom-cut blanks can reduce roughing time on large parts.
Material price is only part of the equation. Machining time, scrap rates, and field failures matter more over a production run. A cheaper nylon part that drifts out of tolerance in service can cost far more than a stable acetal part. Evaluate total cost per functioning part, not per kilogram of resin. When the choice is close, prototype in both materials and test.
Guidance for Bearings, Gears, and Sliding Parts
For plain bearings and bushings, start with Delrin when the design depends on tight clearances, low moisture uptake, or operation in wet environments. Many food-contact designs also default to acetal because approved grades are widely available. Choose nylon when loads are high, speeds are low, and some dimensional change is acceptable.
For gears, acetal is the default for instrument and actuator gears that must hold backlash over years and humidity swings. Nylon gears handle higher torque and shock, especially in lubricated gearboxes, and they tend to run quieter under heavy loads. Many gearbox designs pair a nylon gear with a steel pinion to balance strength, wear, and noise.
For sliding parts like guide blocks and wear pads, either can work. Pick nylon for impact and abrasion, acetal for precision. For outdoor use, specify UV-stabilized grades, because standard versions of both resins degrade in direct sunlight. In every Delrin vs nylon choice, let the harshest condition in your application make the call, then validate with prototypes. If one part must handle both sliding and impact, consider nylon for the body and an acetal insert for the precision surface.
Frequently Asked Questions
Is nylon ever a good choice for precision gears?
Yes. Nylon gears perform well under higher torque and impact loading, particularly in lubricated or oil-bathed systems. The key is to machine them from conditioned stock and to design backlash that accounts for moisture-driven swelling. Where gear geometry must stay stable across humidity cycles without lubrication, acetal is the safer option.
How much does moisture change machined nylon parts?
Nylon absorbs and releases water continuously, so dimensions move with humidity. The change can reach a few percent in extreme conditions, which is enough to affect press fits and sliding clearances. Drying or conditioning parts before final machining reduces the effect. For critical fits, machine acetal instead.
Which material is easier to CNC machine?
Delrin is the easier material for most shops. It cuts cleanly, resists melting, and holds tolerances without conditioning. Nylon can be machined to a high standard too, but it needs sharper tools, controlled heat, and planning for stress relief and moisture uptake. For first-time users, acetal gives more predictable results in a Delrin vs nylon evaluation.
For related information, see our guide to nylon cnc machining.