Delrin vs Nylon: CNC Machining Differences
Quick Answer
Delrin vs nylon is mainly a question of dimensional stability versus toughness and moisture behavior. Choose Delrin, also called acetal or POM, when the CNC plastic part needs crisp machining, tight dimensions, low friction, low moisture absorption, and stable geometry. Choose nylon when the part needs toughness, wear resistance, impact strength, and a little more flexibility, but only if the design can tolerate moisture absorption and dimensional movement. For precision CNC plastic parts, Delrin is usually the safer default. Nylon is excellent when the part works as a wear component and the environment is understood.
This is not a plastic encyclopedia. The real question is what happens during machining and after the part leaves the machine. Delrin CNC machining usually gives clean chips, sharp edges, smooth bores, and predictable inspection. Nylon CNC machining can produce strong, durable parts, but it can absorb moisture, move after machining, deflect under clamping, and change size between a dry inspection room and a humid working environment.
Comparison Table
| CNC machining factor | Delrin / POM | Nylon |
|---|---|---|
| Best use | Precision bushings, gears, rollers, spacers, fixtures, low friction parts | Wear pads, guides, rollers, impact parts, tough mechanical components |
| Machinability | Excellent, crisp chips, clean detail | Good, but more flexible and more sensitive to heat and clamping |
| Moisture absorption | Low | High compared with Delrin |
| Dimensional stability | Generally better | Can change with humidity and conditioning |
| Wear resistance | Good low friction behavior | Very good toughness and wear performance in many applications |
| Surface finish | Smooth machined finish is easier | Can be good, but burrs and fuzzing need control |
| Cost | Often moderate to higher depending on grade | Often cost effective, but grade and conditioning matter |
Material Explanation
Delrin is a well known trade name for acetal homopolymer. In many engineering discussions, Delrin and POM are used almost interchangeably, although POM can include homopolymer and copolymer grades. The practical machining point is that Delrin is hard, stable, low friction, and easy to cut accurately. It is commonly used for precision gears, rollers, bushings, wear strips, spacers, valve components, electrical insulators, and fixture details.
Nylon is a family of polyamide materials, including PA6, PA66, oil filled nylon, glass filled nylon, and cast nylon. It is valued for toughness, wear resistance, impact strength, and mechanical durability. Nylon can be a better choice than Delrin when a part must absorb shock, run as a wear pad, or survive rougher mechanical contact. The tradeoff is moisture. Nylon absorbs water from the air and from direct contact with liquids. That moisture can change dimensions and mechanical behavior.
POM vs nylon is therefore not only about strength. It is about how the part will be machined, inspected, stored, assembled, and used. A dry nylon part measured after machining may not be the same size after it sits in a humid plant. A Delrin part may hold dimensions better, but it may not be as tough under certain impact or abrasive conditions.
CNC Machining Considerations
Delrin CNC machining is usually straightforward when the cutter is sharp and the workholding is clean. The material cuts with crisp chips, holds edges well, and can produce fine machined surfaces. It is a good choice for parts with tight bores, grooves, counterbores, pockets, and small details. It also tends to deburr more cleanly than nylon. This is one reason Delrin is often selected for precision plastic components.
Nylon CNC machining needs more care. Nylon is tougher and more flexible, so it can deflect under clamping pressure. It can also generate stringy chips or fuzzy edges if the tool is dull, the feed is wrong, or heat builds up. Coolant, air blast, chip evacuation, and tool sharpness matter. If the part is thin or has tall ribs, the fixture must support the work without squeezing it out of shape.
Heat is a shared risk for both materials. Plastics do not conduct heat like aluminum or steel. If the cutter rubs instead of cuts, the surface can smear, melt, or grow burrs. The solution is not simply slower machining. Often the better approach is a sharp polished tool, enough chip load to cut cleanly, controlled spindle speed, good chip evacuation, and light finishing passes.
Threads and inserts should be reviewed early. Delrin can hold machined threads for light duty, but repeated assembly may still benefit from metal inserts. Nylon threads can be tough, but moisture and creep can affect long term preload. If the part will be assembled many times, use threaded inserts, shoulder bolts, bushings, or a design that avoids relying on small plastic threads alone.
Tolerance, Surface Finish, and Cost
Delrin normally wins when tight tolerance and dimensional repeatability are the priority. It has low moisture absorption and good dimensional stability, so inspection results are easier to trust. That does not mean every Delrin part is automatically precise. Thin walls, long slots, asymmetric material removal, and internal stress can still cause movement. But compared with nylon, Delrin is usually more predictable for close fitting CNC plastic parts.
Nylon can hold useful tolerances, but the tolerance must make sense for the environment. If a nylon part runs in a wet area, near coolant, outdoors, or in a humid factory, the final working size may differ from the dry machined size. For nylon, the drawing should define whether dimensions are checked dry, conditioned, or after environmental exposure. This is especially important for bushings, rollers, guides, and sliding parts.
Surface finish also differs. Delrin often produces a smooth, glossy or satin machined surface with clean tool marks. Nylon can produce a good finish, but it may show fuzz, stringing, or soft burrs if the process is not tuned. Very sharp cutters and careful deburring are important. If a part needs a sealing face, bearing contact face, or sliding surface, the required surface finish should be marked on the drawing.
Cost depends on grade, stock size, tolerance, and quantity. Standard nylon can be economical for larger wear parts, while specialty filled nylon grades may cost more. Delrin is often worth the price when it reduces scrap, inspection disputes, or assembly problems. A cheap material is not cheap if it moves out of tolerance after delivery.
Quote and Inspection Notes for CNC Buyers
When requesting a quote, do not only write plastic on the drawing. State the exact material, grade, color, and whether an equivalent material is allowed. For example, black Delrin, natural acetal copolymer, PA6 nylon, PA66 nylon, oil filled nylon, and glass filled nylon can all behave differently during machining. If the part will be used in a wet area, near coolant, outdoors, or inside moving equipment, tell the supplier before machining starts. That information changes material selection, tolerance review, and inspection planning.
Inspection notes are especially important for nylon. If the drawing has tight tolerances, define the inspection condition. A dry nylon part measured right after machining may not represent the final working size after moisture conditioning. For Delrin, the issue is usually less severe, but temperature, thin wall geometry, and clamping stress can still affect precision parts. For both materials, critical bores, sliding faces, press fit areas, and insert locations should be called out clearly so the supplier knows which features deserve the most process control.
When to Choose
Choose Delrin when the part needs low moisture absorption, stable dimensions, smooth machined surfaces, low friction, and clean detail. Good examples include precision spacers, valve parts, gears, sliding blocks, electrical insulators, rollers, bushings, datum pads, and fixtures that must remain stable during inspection and assembly.
Choose nylon when the part needs toughness, wear resistance, impact resistance, and some flexibility. Good examples include guide rails, wear pads, rollers, pulley wheels, bushings, impact blocks, and replacement parts for industrial equipment. Nylon is especially useful when a part must handle rubbing contact, shock, or dirty mechanical service, but the design must allow for moisture and possible size change.
A practical rule is simple: choose Delrin for precision and stability; choose nylon for toughness and wear when the environment is known. If both materials seem possible, test the real geometry, not only a material sample. The same material can behave differently in a thin wall part, a thick bushing, or a long slotted guide.
Related DAXIN Services
DAXIN provides CNC machining services for engineering plastics and production plastic components, including milling, turning, drilling, tapping, inserts, deburring, inspection, and small batch production. We can machine Delrin, nylon, acrylic, polycarbonate, PEEK, PTFE, UHMW, and other engineering plastics depending on the application. For more general material decisions, see our CNC machining service page.
For CNC plastic parts, we prefer to review the CAD model before quoting. Plastic machining is sensitive to clamping, heat, tool sharpness, wall thickness, and inspection condition. A small design change, such as adding a radius, increasing wall thickness, changing an insert, or relaxing a noncritical tolerance, can reduce cost and improve reliability.
FAQ
1. Is Delrin better than nylon for CNC machining?
Delrin is usually better for precise machining, clean edges, and dimensional stability. Nylon may be better for toughness, impact, and wear applications.
2. What is POM vs nylon?
POM is acetal, often associated with Delrin. Nylon is polyamide. POM is usually more dimensionally stable, while nylon usually absorbs more moisture and offers strong toughness.
3. Does nylon absorb moisture after machining?
Yes. Nylon can absorb moisture from air or direct contact with liquid, which can change dimensions and mechanical behavior.
4. Which material gives a better surface finish?
Delrin often gives a smoother and cleaner machined finish. Nylon can finish well, but it needs sharp tools and good burr control.
5. Which material is better for bushings?
Both can work. Delrin is better when stable size and low friction are important. Nylon is often better when toughness and wear under rough service matter.
6. Can Delrin and nylon hold tight tolerances?
Delrin usually holds tight tolerances more predictably. Nylon can hold useful tolerances, but humidity, conditioning, and flexibility must be considered.
7. Are Delrin parts expensive?
Delrin can cost more than some nylon grades, but it can reduce machining and inspection problems when stability is important.
8. Should plastic parts use metal inserts?
For repeated assembly, higher torque, or maintenance cycles, inserts are often safer than relying on small plastic threads.
9. Which material is better for wet environments?
Delrin usually moves less with moisture. Nylon may still work in wet environments, but the design must allow for moisture absorption.
10. How should I choose for my CAD model?
Start with tolerance, moisture exposure, load, wear, surface finish, and cost. If dimensions are critical, start with Delrin. If toughness and wear are dominant, review nylon.
CTA
Need help choosing Delrin vs nylon for a CNC machined plastic part? Upload your CAD file and get a quote from DAXIN. We can review material choice, machining risk, tolerances, inserts, surface finish, and cost before production starts.