Robot Plastic Gears in POM: Material, Design & Molding Guide
POM (acetal, sold as Delrin) is the default plastic for robot gears. It runs quiet, needs no grease, and molds at fleet volume for a fraction of a machined metal gear.
This guide covers where plastic gears belong in a robot, how POM compares to nylon and PEEK, and the molding details that decide whether a gear runs smooth or strips its teeth. It expands the robotics & AI hardware overview.
Plastic robot gears at a glance:
- POM (Delrin) is the default — low friction, dimensional stability, self-lubricating.
- Nylon (PA) takes more shock but absorbs moisture, which shifts tooth clearance.
- PEEK handles heat and load, but costs far more and is rarely molded for gears.
- The honest limit: high-shock, near-zero-backlash joints still belong to hardened steel.
Why plastic gears in robots?
Plastic gears have replaced metal in millions of drivetrains. Robots follow the same logic for four reasons.
- Quiet. Plastic-on-plastic mesh runs softer than metal-on-metal contact.
- Self-lubricating. POM has natural lubricity, so many drives run dry.
- Light. Lower rotating mass means smaller motors and less energy per cycle.
- Cheap at volume. Molding beats hobbing metal once tooling is amortized.
Molding adds one more edge: part integration. A gear can mold with a hub, cam, or ratchet as a single part. That cuts component count and assembly cost.
POM: the default gear material
POM combines rigidity with natural lubricity. That mix suits precision drives that need smooth, quiet motion. It holds dimension well because it barely absorbs water.
Typical numbers: tensile strength around 60–70 MPa, flexural modulus near 2.7 GPa. It works in dry or lightly lubricated drives up to roughly 80 °C. Above that, derate it — at 80 °C its bending strength drops to about 60% of the room-temperature value.
POM vs nylon vs PEEK — pick by the job
There is no single best plastic gear material. It depends on load, temperature, moisture, and budget. Use this table as a shortlist.
| Material | Strength / temp | Watch out for | Best robot use |
|---|---|---|---|
| POM (acetal / Delrin) | 60–70 MPa; to ~80 °C | Lower impact; can go brittle under shock in cold | Default choice — precision, low-noise, light-duty drives |
| Nylon (PA66) | ~80 MPa unfilled | Absorbs moisture — dimensions swell, factor into clearance | Impact and shock loads; cost-sensitive parts |
| Glass-filled PA66 | Up to ~180 MPa | Fill affects wear, noise, and mating-gear choice | Higher-load joints where stiffness matters |
| PEEK | High load; −60 to 260 °C | Very high cost; rarely injection-molded for gears | Hot actuators near motors; sterilizable or chemical exposure |
A note on nylon moisture: it is the most common design miss. Nylon swells as it takes up water. Design the tooth clearance for the wet state, not the dry molded state, or the mesh binds.
Where plastic gears do not belong
A good supplier tells you the limit up front. Here it is.
Being clear about this builds trust with your engineering buyers. It also points them to the parts where molding genuinely wins: grippers, sensor gimbals, secondary actuators, and consumer-grade joints.
Molding a precision gear right
A plastic gear is a molding problem before it is a material problem. Tooth geometry lives or dies on melt control and repeatability. These points decide the result.
Gate placement
A center or diaphragm gate feeds the gear evenly from the middle. That keeps the pitch circle round and concentric. A single side gate skews flow and distorts roundness.
Weld lines off the teeth
Where two flow fronts meet, they form a weld line — a weak seam. Gate and vent so any weld line lands away from loaded tooth roots.
Shrinkage compensation
POM shrinks as it cools. The tool must cut the teeth oversized by the exact shrink rate, so the finished tooth profile hits spec. This is where mold-maker experience shows.
Uniform wall & web
Thick hubs next to thin rims cool at different rates. That warps the gear and sinks the surface. Balance the web thickness, or core the hub, to cool evenly.
Molding vs machining gears
Machined or hobbed plastic gears suit prototypes and low volume. Molding takes over at scale.
| Machined / hobbed | Injection molded | |
|---|---|---|
| Best volume | Prototype to hundreds | Thousands and up |
| Per-part cost at volume | High | Low |
| Feature integration | Limited | Hub, cam, ratchet in one shot |
| Upfront cost | Low | Tooling investment |
A practical path: hob a POM prototype to validate the mesh, then mold the same material for production. Same polymer, no property surprise at ramp.
Need a molded gear for your robot?
Send your gear drawing or DXF with the module, tooth count, and load. We will advise the resin, compensate the shrink, and quote the mold and parts.
Upload your gear drawingRelated guides
Humanoid robot molded parts overview →
Insert molding for robotics →
Robot plastic material selection guide →
Frequently asked questions
What is the best plastic for robot gears?
POM (acetal, Delrin) for most cases — low friction, quiet, dimensionally stable. Nylon for shock loads, glass-filled nylon for higher stiffness, PEEK for hot or chemical environments.
Are plastic gears strong enough for robots?
For light and medium drives, yes. For high-shock, near-zero-backlash actuators in a humanoid hip or knee, no — those need hardened steel. Plastic suits the drives around them.
Do POM gears need lubrication?
Often not. POM has natural lubricity and runs many drives dry or lightly lubricated. That is a key reason it is the default plastic gear material for robots.
Why do nylon gears change size?
Nylon absorbs moisture and swells. Dimensions shift between the dry molded state and the in-service wet state. Design tooth clearance for the wet state to avoid binding.
Can you mold a gear with an integrated hub or cam?
Yes. Injection molding forms the gear, hub, cam, or ratchet as one part. That cuts component count and assembly cost compared with machining separate metal pieces.
Is PEEK injection molded for gears?
Rarely. PEEK tooling and material cost are both very high. It is usually machined for gears, and reserved for hot, high-load, or sterilizable applications where cheaper resins fail.
Bottom line. POM is the right starting point for most robot gears — quiet, self-lubricating, stable, and cheap to mold at volume. Nylon and PEEK cover the edges. The hardest joints still belong to steel, and a good supplier says so. Where molding wins, the tool and the process decide the tooth quality. Send a gear drawing — we will tell you what molds cleanly and how we will hold the profile.
