Best Plastics for Gears
Plastic gears have displaced metal in millions of drive trains — printers, power tools, appliances, medical devices, automotive actuators, and industrial machinery — because they run quieter, self-lubricate, resist corrosion, and are cheaper to injection-mold in volume. Choosing the right polymer determines whether the gear survives rated torque and temperature, or strips teeth and fails prematurely. This guide covers every serious candidate from commodity acetal to high-performance PEEK and phenolic laminates, with specific data on tooth strength, temperature range, and module considerations.
TL;DR
- Delrin is the default: low friction, dimensional stability, easy to machine or mold, works in dry or lightly lubricated drives up to 180°F.
- Nylon tolerates impact and shock loads better than acetal and costs less, but moisture swell must be factored into tooth-clearance design.
- PEEK extends the operating envelope to 480°F and handles the highest torque of any unfilled thermoplastic gear material.
- PEI/Ultem offers a middle ground at 340°F continuous, lower cost than PEEK, with good chemical resistance.
- PET (Ertalyte) resists fatigue and creep better than nylon at moderate loads — the underrated choice for continuous-duty timing gears.
- Phenolic laminates (cotton or glass fabric base) are the traditional heavy-industrial choice: dampen vibration, excellent in oil-bath drives, limited to ≤200°F.
- Plastic gears generate heat internally at high speed — limit pitch-line velocity and verify tooth temperature, not just ambient temperature.
Delrin — The Workhorse Gear Material
Acetal homopolymer (Delrin) is the most widely used material for molded and machined plastic gears, and it earns that position. Its combination of dimensional stability (0.2% moisture absorption at saturation), low coefficient of friction against steel (0.20–0.35), and resistance to fatigue cycling under tooth-bending stress make it reliable across a wide range of light-to-medium-duty drive applications.
Acetal gear design specifics
- Tooth strength: Lewis bending stress allowable for acetal gear teeth runs approximately 5,000–6,000 psi at room temperature, declining 20–30% at 160°F. Apply a service factor of 1.5–2.0 for shock loads.
- Temperature limits: Continuous use to 180°F (82°C). Pitch-line temperatures in high-speed gears can exceed ambient by 30–60°F — measure or calculate operating tooth temperature before specifying.
- Module/pitch: Acetal is readily moldable in fine pitch (20–48 DP) and machined in coarse pitch (4–12 DP). For machined gears, minimum module 0.8 (≈ 32 DP) is practical; below this, tooth fragility limits cutting tool options.
- Mating gear: Acetal gears run best against steel or against themselves. Acetal-on-acetal pairs generate less heat than dissimilar polymer pairs in many cases.
PTFE-filled acetal gears
Adding 15% PTFE to acetal reduces the friction coefficient to 0.05–0.10 and extends the self-lubricating life of gears in sealed or unlubricated drives. Tooth strength is slightly reduced (flexural modulus drops ~10%), so verify Lewis stress calculations on PTFE-filled grades separately from standard acetal.
Nylon — Impact-Tolerant Gear Material
Nylon 6 and 6/6 are the highest-volume injection-molded gear material globally because of their combination of toughness, low cost, and fatigue resistance. The elongation-to-break (20–40%) and impact strength (2.0 ft·lb/in notched) allow nylon gears to absorb shock loads — jams, start-up torque spikes, and reverse-direction shocks — that would crack acetal teeth.
Moisture compensation in nylon gear design
Nylon absorbs 1.5–3.0% moisture, which causes radial swell of 0.3–0.7% depending on grade and environment. A 3.000 in PD gear machined to tight tolerance in a dry shop will expand its pitch diameter by 0.009–0.021 in after equilibrating to 65% RH. Design the mating center distance or tooth clearance to accommodate the worst-case swell. Nylon 6/12 absorbs only about 0.7% moisture — specify it when dimensional stability under humidity variation is critical.
Nylon gear grades for specific applications
- Nylon 6/6 (unfilled): General injection-molded gears, automotive, consumer products.
- Nylon 6/6 + MoS₂: Reduces friction, improves run-in behavior for unlubricated gears.
- Nylon 6/6 + glass fiber (30–40%): Raises tooth strength 50–80% but increases abrasiveness against mating teeth — avoid glass-filled nylon against soft counter-gears.
- Nylon 12: Lower moisture absorption than 6/6, better chemical resistance; used in fluid-handling drives.
PEEK — High-Load, High-Temperature Gears
PEEK is specified when neither acetal nor nylon can survive the operating conditions. Applications include medical sterilizable instrument gears, aerospace actuator drives, semiconductor handling equipment, and chemical plant drives exposed to aggressive fluids.
PEEK gear performance envelope
Unfilled PEEK sustains tooth-bending stresses up to ~8,000–10,000 psi at 300°F — roughly double what acetal can handle at that temperature. Carbon-fiber-filled PEEK (30% CF) raises this further to ~14,000 psi and dramatically reduces the coefficient of thermal expansion, tightening pitch-diameter dimensional control at elevated temperature. The trade-off with carbon-filled PEEK is abrasiveness against soft mating gears — pair CF PEEK only with hardened steel or another CF PEEK gear.
PEEK gear machining considerations
PEEK is not typically injection-molded for gear production (tool cost is high; material cost is very high). Machined PEEK gears from rod or plate stock are standard. Use sharp carbide tooling, 0.010–0.020 in depth of cut, coolant (water-soluble or air), and avoid dwelling in the cut. Minimum practical module for machined PEEK is approximately 0.5 (≈ 50 DP in inch pitch); fine-pitch tooth profiles in PEEK require careful tool geometry to avoid micro-chipping at the tooth tip.
PEI / Ultem — High-Temperature Thermoplastic Gears
Polyetherimide (PEI), sold as Ultem (SABIC), is a cost-effective stepping stone between acetal/nylon performance and the PEEK tier. Continuous use temperature is 340°F (170°C), flexural strength is approximately 20,500 psi, and the material is inherently flame-retardant (UL 94 V-0) and hydrolysis-resistant.
When to specify Ultem over PEEK for gears
- When operating temperature is 210–340°F and PEEK cost (typically 5–8× Ultem) is unjustified.
- When the gear is inside an electronic device and flame retardancy is required.
- When the mating surface is a metal worm or rack that would overheat acetal but doesn't require PEEK's full temperature range.
PEI is injection-moldable at production scale — unlike PEEK, which is usually machined for gears. Ultem 1010 is the unreinforced base grade; Ultem 2300 (30% glass) raises strength and stiffness. Ultem 1010 is also USP Class VI and FDA compliant, extending it to medical gear drives.
PET / Ertalyte — Fatigue-Resistant Timing Gears
PET (polyethylene terephthalate) in its engineering grade form — Ertalyte (Quadrant), Sustadur PET — is the preferred material for continuously loaded timing gears, indexing gears, and worm gear driven shafts where creep resistance and fatigue life are the governing criteria.
PET vs nylon for timing gears
At 23°C and moderate loads, PET and nylon perform similarly. At elevated temperature (above 150°F) or under continuous static-plus-cyclic load, PET's lower creep rate — approximately 50% lower than nylon 6/6 at 3,000 psi and 150°F — prevents the gradual pitch-circle growth that causes timing error in precision drives. Moisture absorption is 0.1% (versus nylon's 1.5–3.0%), so tooth clearances remain consistent across seasons.
PET is not injection-moldable into fine-pitch gears without specialty mold tool design. It is primarily a machined gear material, available in rod up to 12 in diameter and plate to 4 in thick.
Phenolic Laminates — Heavy Industrial Gear Material
Cotton-fabric phenolic and glass-fabric phenolic laminates (NEMA CE, LE, G-7) are the traditional choice for large-pitch gears in heavy industrial drives: mill drives, crane hoists, and large reduction gearboxes. These materials date to the early 20th century and remain specified because they excel in oil-bath lubrication conditions, damp vibration and noise effectively, and allow large gear blanks to be cut from thick laminate plate.
Phenolic gear properties
- Damping: Cotton phenolic (NEMA LE) has excellent vibration-damping — gears mesh nearly silently at low-to-moderate pitch-line velocity even in heavy drives.
- Oil compatibility: Phenolic laminates are stable in mineral oil and most gear oils. Avoid alkaline cleaning agents, which can swell and delaminate cotton-base grades.
- Temperature ceiling: 200°F continuous (in oil). Above this, the phenolic resin softens and the laminate can delaminate under tooth-bending stress.
- Machinability: Cuts cleanly with carbide tooling. Phenolic dust is irritating — use dust collection and respiratory protection.
For coarse-pitch, slow-speed industrial gears (module 3–12, pitch-line velocity under 2,000 ft/min, continuous duty in oil), phenolic remains the price-performance leader. Specify glass-fabric phenolic (NEMA G-10 or G-7) where moisture or weak alkalis are present — cotton-base grades will swell in humid environments.
How to Choose: Decision Matrix
1. What is the peak operating temperature?
- Below 180°F → Acetal or nylon.
- 180–210°F → Nylon 6/6 (dry), or PET if creep is a concern.
- 210–340°F → PEI/Ultem.
- 340–480°F → PEEK.
- Above 480°F → No unfilled thermoplastic; consider metal or ceramic.
2. Is the drive subject to shock or jam loads?
- Yes → Nylon preferred over acetal (higher impact toughness).
- No (smooth, continuous load) → Acetal, PET, or PEEK.
3. Is lubrication available?
- Oil-bath or greased → Phenolic (heavy industrial), nylon, or acetal.
- Dry or intermittently lubricated → Acetal (PTFE-filled for lowest friction), nylon MoS₂-filled.
- No lubrication whatsoever → PTFE-filled acetal or PEEK bearing grade (with graphite filler).
4. What is the gear pitch and module?
- Fine pitch (DP > 24, module < 1) → Acetal or nylon (moldable); PEEK (machined).
- Coarse pitch (DP 4–12, module 2–6) → Acetal, nylon, PET, or phenolic (machined).
- Very coarse pitch (module > 6) → Phenolic laminate plate or nylon castings.
5. Is FDA compliance required?
- Yes → Acetal natural, nylon natural, PEEK, PET, Ultem 1010. Not phenolic.
Sizes & Forms Commonly Stocked
| Form | Size Range | Common Materials |
|---|---|---|
| Rod (gear blank) | 1 in – 12 in diameter | Acetal, nylon, PEEK, PET |
| Plate (spur gear blank) | ½ in – 4 in thick | Acetal, phenolic, nylon |
| Tube (hollow gear blanks) | 2 in – 8 in OD | Nylon, acetal, PEEK |
| Laminate plate | 1 in – 4 in thick, 36 × 48 in | Phenolic cotton, phenolic glass |
Large-diameter gear blanks (above 8 in OD) in nylon are often cast rather than machined from extruded rod. Cast nylon blanks have more uniform properties in the radial direction and less residual stress.
Spec Sheet & Test Data
- Delrin hub — friction data, fatigue curves
- Nylon hub — moisture absorption, impact strength by grade
- PEEK hub — high-temp mechanical data, filled grades
- PEI/Ultem hub — thermal, electrical, FDA status
- PET/Ertalyte hub — creep data, fatigue endurance
- Phenolic/Glass hub — NEMA grades, oil compatibility
FedMat stocks acetal, nylon, PEEK, and phenolic in gear-blank rod and plate, cut to length. Custom machined gears available on request. Get a quote with your module, number of teeth, face width, and bore requirements.
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