Nylon CNC Machining Services: What to Check Before You Order
Nylon machines easily until moisture, heat and clamping start moving dimensions. This guide is for design engineers and buyers picking nylon CNC machining services for PA parts. Read it and you can judge grade, tolerance, finish and shop capability before you release the order.
Key takeaways
Which nylon grade fits which part
Use this table to match the grade to the load, the environment and the tolerance you need.
| Grade | Best for | Watch out for | Typical use |
|---|---|---|---|
| PA6 cast | Large stable blanks, tight flatness | Thicker sections hold more moisture | Fixtures, wear pads, insulators |
| PA6 extruded | Long thin profiles, good surface | Directional strength along the extrusion | Bushings, spacers, guides |
| PA66 | Higher stiffness and heat resistance | Brittle under impact when very dry | Gears, brackets, clips |
| PA6-GF30 | Stiffness and creep resistance | Glass dulls tools fast; edge chipping | Structural brackets, housings |
| PA12 | Low moisture pickup, stable parts | Lower strength than PA6 or PA66 | Fuel lines, precision spacers |
| Oil-filled PA | Low friction, quiet running | Filler can smear on fine finishes | Bearings, sliding plates |
Pick the shop that controls moisture, not just the machine
Nylon rewards a supplier who dries stock, uses sharp polished tooling and measures after the part settles. If the quote does not mention those three things, keep looking.
What makes nylon hard to machine to tolerance
Polyamide is tough, slides well and resists many chemicals, which is why it replaces bronze and steel in wear parts. Those same properties make it awkward on a mill. The material is soft enough to cut fast, yet it deflects under tool pressure and springs back after the cutter passes.
The bigger issue is water. Nylon is hygroscopic. A dry blank that measures 50.00 mm can grow several hundredths of a millimeter as it takes up moisture from shop air. If you inspect a part minutes after cutting and again a week later, the numbers will not match.
Heat is the third factor. Nylon softens at low temperatures compared with metals. Rubbing instead of cutting melts the surface, produces stringy chips and leaves a rough finish. The melt zone also drags material back into the cut, so the next pass cuts a different depth.
None of this makes nylon a bad choice. It means the process has to be controlled: dry stock, sharp tooling, cooled cuts and a measurement plan that accounts for moisture.
- 1HygroscopicAbsorbs moisture from air; dimensions drift after machining.
- 2Low melting pointRubbing heat smears the surface and clogs flutes.
- 3Stringy chipsLong chips wrap the tool and scratch finished faces.
- 4Elastic recoveryMaterial springs back, so spring passes matter.
How to judge nylon CNC machining services
Start with the machine list. Nylon parts often need multiple faces, deep pockets or thin walls. Three-axis mills handle simple plates fine. Five-axis centers cut angled faces and undercuts in one setup, which matters when you cannot re-clamp a soft part without marking it.
Ask how the shop stores and dries stock. A supplier that keeps PA on an open rack in humid air will struggle with tolerance. Controlled storage and a drying step before machining are the difference between a stable part and one that moves after shipping.
Tooling tells you a lot. Nylon wants sharp, polished flutes with high helix angles for chip evacuation. A shop that runs the same end mills it uses on aluminium will burnish the surface and fight chip wrap all day.
Finally, look at the inspection routine. Nylon needs measurement after it has settled, not straight off the machine. Ask whether the shop records temperature and humidity, and whether it will hold the part before final inspection.
- 1Machine mixFive-axis and mill-turn reduce setups on soft parts.
- 2Drying routineControlled stock before cutting, not after.
- 3Tool geometrySharp polished flutes, high helix, positive rake.
- 4Inspection timingMeasure after the part equalizes, not at the machine door.
Setting realistic tolerances and finishes
A general machining tolerance of ±0.005 mm is achievable on nylon for small features in stable, low-moisture grades such as PA12 or glass-filled PA6. On large unfilled PA6 parts, that number is optimistic. Wall thickness above 20 mm holds more moisture and moves more between cuts.
Be selective. Put the tight tolerance only on the features that mate with something else: bore diameters, pin holes, sealing faces. Leave cosmetic surfaces and clearance pockets at ±0.1 mm. Tightening everything raises cost and does not improve function.
Surface finish follows tooling and feed. As-machined nylon comes off around Ra 1.6–3.2 μm. With sharp tooling, light finishing passes and good chip evacuation, Ra 0.8–1.6 μm is realistic on flat and cylindrical faces. Asking for Ra 0.2–0.8 μm on nylon usually means polishing, and polishing soft polymer can round edges.
Threads deserve a note. Cut threads in nylon hold well but strip if the wall is thin. Specify a coarser pitch and a longer engagement than you would use in aluminium.
- 1Tight where it matesBores and sealing faces only.
- 2Loose elsewhere±0.1 mm on clearance and cosmetic features.
- 3Finish floorRa 0.8–1.6 μm is a practical target.
- 4ThreadsCoarser pitch, longer engagement.
What drives price and delivery on PA parts
Material is a small share of the cost on most nylon jobs. Setup, programming and inspection dominate. A part that needs three setups costs more than one that runs in a single five-axis cycle, even when the geometry is similar.
Glass-filled grades cost more to cut than unfilled ones. PA6-GF30 wears tools quickly, so shops either change tools more often or run slower feeds. Both show up in the quote. If your design does not need the stiffness, unfilled PA6 or PA66 will be cheaper to machine.
Quantity changes the method, not just the price. One prototype and a 10,000-part run are different problems. Prototypes usually come off a mill. Larger runs may move to a lathe with bar feed or to a fixture that holds several parts at once.
Lead time depends on stock. Common grades and thicknesses are usually on hand. Special colors, filled compounds or very thick plate may need to be ordered, which adds days before the first cut.
- 1Setups dominate
- 2Filler costs
- 3Volume changes method
- 4Stock availability
Step by step: qualifying a nylon supplier
Work through these before you send the purchase order.
- 1Send the drawing with grade and moisture stateState PA6, PA66, PA12 or glass-filled, plus whether the part will run dry or in humidity. Note any features that must hold tolerance after equilibration.
- 2Ask for the machining planWhich machine, how many setups, what tooling. A shop that answers in specifics is usually the one that has cut PA before.
- 3Confirm the drying and storage routineAsk how long stock is dried, at what temperature, and how it is stored between operations. Vague answers are a warning sign.
- 4Agree on the inspection methodCMM, optical or hand tools, and when the part is measured. Ask for a first article report on the first part of the run.
- 5Set the tolerance mapMark which dimensions are critical and which are free. This alone can cut cost without touching function.
- 6Request a sample or first articleRun one part, measure it after it settles, then release the batch. Cheaper than scrapping a full order.
- 7Confirm packagingNylon scratches. Ask for soft separators and no loose bulk packing on finished faces.
Common questions
Does nylon need annealing before machining?
Stress-relief annealing helps on thick sections and glass-filled grades. It reduces internal stress that would otherwise pull a part out of flat after cutting.
Thin plates and small turned parts rarely need it. Ask the shop whether the stock is already stress-relieved from the supplier.
How much does a nylon part move after machining?
Unfilled PA6 can shift several hundredths of a millimeter over the first days as it takes up moisture. The amount depends on wall thickness, shop humidity and how dry the stock was.
PA12 picks up less water and moves less. If dimensional stability is the main concern, PA12 or a glass-filled grade is usually the safer pick.
Can you hold ±0.005 mm on nylon?
Yes, on small features in stable grades and with controlled stock. It is not realistic across a large unfilled PA6 part.
We recommend a tolerance map: tight on mating features, looser on everything else. That keeps cost down and still fits the assembly.
What surface finish can nylon take?
As-machined finish lands around Ra 1.6–3.2 μm. With sharp tooling and light finishing passes, Ra 0.8–1.6 μm is achievable on flat and cylindrical faces.
Very fine finishes require polishing, which can round edges and change dimensions on soft polymer.
Is there a minimum order quantity?
No minimum. We run from a single prototype to 10,000+ part runs.
Prototypes usually come off a mill; larger quantities move to fixtures or bar-fed turning.
How do you handle confidentiality on new designs?
Uploads are secure and confidential. An NDA is available on request before you share drawings.
We can also quote from a simplified model if you prefer to keep full geometry internal at the first stage.
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