Plastic Double Spur Gear

A plastic double spur gear is a compound gear with two sets of spur teeth on a single hub body — one gear on each level of the two-stage compound gear. The two sets of teeth have different tooth counts (and often different modules for the two stages), so the double gear simultaneously meshes with two other gears: the larger gear receives input from the previous stage, and the smaller gear drives the next stage. This two-ratios-in-one-body design eliminates one bearing shaft in the gear train, saves housing space, and reduces the total part count compared with two separate gears on separate shafts. Korea Ever-Power's plastic double spur gears are available in PA, POM, UHMWPE, ABS, PTFE, PPS, and PEEK, modules M1–M12, to ISO/DIN/ANSI/JIS standards, precision DIN6–DIN9.

Korea Ever-Power's plastic double spur gears are used in robotics, toys, small machinery, medical devices, printers, cameras, and office automation — wherever a compact two-stage speed reduction must fit in a minimum housing volume without an intermediate shaft. Sample lead time: 20 business days. Bulk: 25 business days. Custom per drawing or sample.

POM Compound

Custom Multi-Stage

Complete Gear Set

Two Gear Stages, One Body

The double spur gear has a large-diameter gear (Z₁ teeth) and a small-diameter gear (Z₂ teeth) on the same hub, rotating together on the same shaft at the same angular velocity. The large gear meshes with the motor gear (or previous stage), receiving input rotation. The small gear simultaneously meshes with the next stage's large gear, transmitting the rotation at the compound gear's fixed angular velocity. The overall ratio of the double gear stage is (input gear teeth / Z₁) × (Z₂ / next stage gear teeth) — two ratios combined in one intermediate stage without a dedicated shaft bearing for the intermediate shaft.

Bidirectional Power Transmission

The plastic double spur gear configuration allows power transmission in both directions — clockwise or counter-clockwise input produces the same gear train output with reversed direction. This bidirectional capability increases the efficiency of the gear system since it enables power to be transmitted in both directions through the same gear train without any switching mechanism. In printer paper feed trains, the same double spur gear set drives forward paper advance and reverse paper return; in camera pan drives, it drives both left pan and right pan from the same motor reversing direction.

Space Saving — One Shaft Eliminated

A two-stage gear train using separate gears requires three shafts (motor, intermediate, output) and two sets of bearings. The double spur gear eliminates the intermediate shaft and its bearings — the compound body carries both the receiving and transmitting gears on a single boss/shaft. This shaft elimination reduces the axial depth and radial envelope of the gear train, enabling it to fit within the compact housing of printers, cameras, and small appliances where every cubic millimetre of housing space is allocated by the product designer.

Ratio Flexibility

The double spur gear's two tooth counts (Z₁ large gear, Z₂ small gear) can be independently specified to achieve the required stage ratio. By choosing Z₁ and Z₂ independently, the designer has complete freedom in the ratio each double gear stage contributes to the overall train ratio — while keeping the axial distance between stages constant (set by the double gear hub design). Multiple double gears in series (three or four stages) can achieve total ratios of 100:1 to 1,000:1 in printer paper path drives, camera zoom mechanisms, and instrument clock drives.

Moulding Considerations

Plastic double spur gears are injection-moulded in a single operation — both the large and small gear tooth sets are formed simultaneously in the same die. This requires the mould to have two different gear tooth cavities at different diameters, both accurately positioned relative to the same centre axis. The single-shot moulding ensures perfect coaxiality between the two gear levels — a critical requirement, since any runout between the two tooth levels causes the gear to wobble on its shaft boss, degrading the meshing of both stages simultaneously.

Compound Gear Printer Example

Korea Ever-Power's classic example: M0.7 double spur gear with 24T large gear and 52T small gear (Delrin 500P, 6.47 g). In the printer drive train, the motor's small steel gear meshes the 24T large gear (24:motor ratio), then the 52T small gear meshes the paper feed roller gear (paper feed ratio × 52/motor). The total ratio is the product of both stages — achieved in a single 6.47 g POM body that fits in the printer mechanism without an intermediate shaft pin.

① Low Cost

One double spur gear replaces two single gears plus one intermediate shaft, two shaft support bosses, and one set of alignment features — all in a single moulded part. This part count reduction lowers the assembly cost per unit more than the slightly higher mould cost for the compound double body. At high production volumes (printer, camera, toy), the cost saving per unit is significant.

② Lightweight

Plastic double spur gears are lighter than equivalent metal gears — and lighter than two separate plastic single gears of the same stages, because the shared hub eliminates material at the shaft connection. For hand-held devices (cameras, power tools, portable medical equipment) where every gram affects user ergonomics, the compound double gear is a reliable path to weight reduction in the drive mechanism.

③ Corrosion Resistance

POM and nylon double spur gears are inherently corrosion-resistant — no surface treatment is needed. In food processing equipment, medical devices, outdoor solar drives, and marine applications, this corrosion immunity is essential and difficult to achieve reliably with metal gears (requiring plating or stainless steel at much higher cost).

④ Noise Reduction

Plastic double spur gears generate less noise than equivalent metal gears — from the inherent damping properties of POM and nylon. In consumer electronics and office automation (printers, cameras, appliances), the lower gear mesh noise of plastic double spur gears contributes to the acoustic design compliance of the overall product without requiring special acoustic enclosures.

⑤ Self-Lubricating

POM and nylon double spur gears run without grease or oil lubrication in their normal operating load range — eliminating maintenance and contamination risk. In sealed printer mechanisms, camera housings, and medical equipment where access for re-lubrication is impossible, the self-lubricating plastic double gear is the only practical choice.

⑥ Easy to Manufacture

Injection moulding the double spur gear in a single shot produces both tooth levels simultaneously with precise coaxiality — something that would be difficult and expensive to achieve by assembling two separate gears on one shaft (requiring press-fitting, keying, or moulding-over). The mould cost is only marginally higher than for a single spur gear, while the assembly cost saving over using two separate gears is substantial.

⑦ Good Wear Resistance

POM and nylon double spur gear materials have good wear resistance under the normal operating conditions for which plastic gears are designed. The low friction coefficient, combined with the self-lubricating property, minimises tooth face wear over the millions of cycles typical of printer and camera mechanism lifetimes. Korea Ever-Power's life test data for POM double spur gears in printer applications shows consistent tooth profile within tolerance after 5 million cycles.

⑧ Bidirectional Power

The double spur gear configuration transmits power in both rotation directions — the drive motor simply reverses to achieve both forward and reverse output through the same gear train. This bidirectional capability without additional mechanism is essential in paper feed drives (advance and return), camera drive mechanisms (left and right pan, zoom in and out), and adjustable seat/mirror actuators (extend and retract).

Robotics

POM and nylon double spur gear stages in small robot joint drive trains and gripper mechanisms. The compact two-stage reduction in one part reduces the number of motor-to-joint drive components in each robot axis, minimising joint mass and moment of inertia — critical for dynamic performance in collaborative and educational robots where the arm must be lightweight for safe human coexistence.

Toys and Entertainment

ABS and nylon double spur gears in battery-powered toys, RC vehicles, and educational robot kits. In toy drives, the low cost, lightweight, and self-lubricating properties of plastic double spur gears exactly match the design requirements — and the bidirectional capability is essential in RC vehicles and toy robots that must both move forward and reverse. At toy price points, the part count saving of the double gear vs two separate gears is decisive.

Printers and Office Equipment

The classic application: POM M0.7 double spur gears (24T + 52T, Delrin 500P, 6.47 g) in laser printer paper feed trains. Multiple double spur gears in series create the paper advance gear train from motor to feed roller — each stage a compact double gear body, with the total train fitting in the 5–8 mm axial depth of the printer mechanism. Bidirectional transmission enables paper feed and reverse-feed in the same gear train.

Medical Equipment

POM double spur gears in medical device drive mechanisms — infusion pump feed drives, diagnostic instrument positioning stages, and surgical instrument actuators. Medical device double spur gears must meet biocompatibility requirements (POM FDA-listed), particle cleanliness (no lubricant contamination), and long service life at specified duty cycles. Korea Ever-Power can provide material certification documentation for medical device qualification.

Solar Energy Equipment

UV-stabilised nylon double spur gears in single-axis and dual-axis solar tracker drive trains. The bidirectional capability enables the tracker to follow the sun from east to west (forward) and return to east before sunrise (reverse) — in the same lightweight, maintenance-free plastic double gear train.

Parking Systems

MC Nylon double spur gears in automated parking system platform drive trains and ticket barrier mechanism drives. The higher load capacity of MC Nylon suits the heavier loads in parking equipment compared with office automation applications, while the self-lubricating and corrosion-resistant properties suit the outdoor and underground parking environments.

What is the difference between a plastic double spur gear and two separate plastic spur gears?

A plastic double spur gear combines two gear stages in a single moulded body on one hub shaft. Two separate spur gears require two individual bodies, two separate shaft pins, and two sets of shaft support bosses in the housing. The double gear reduces part count, eliminates one shaft, saves housing volume, and ensures perfect coaxiality between the two gear levels (since both are formed in the same mould). The trade-off is a slightly more complex mould — but this is easily offset by the reduced assembly cost and simpler housing design the double gear enables.

Can both stages of a plastic double spur gear have different modules?

Yes — the large gear and small gear of a double spur gear can have different modules (e.g., M0.7 large gear meshing with the motor, M0.5 small gear driving the output stage) when the design requires this for matching centre distances or optimising tooth strength at each stage. Korea Ever-Power designs double spur gear stages to customer specification — provide the required stage ratios, centre distances, and torque at each stage for a complete double gear design consultation.

Are plastic double spur gears suitable for high-torque applications?

Plastic double spur gears are suitable for light-to-moderate torque applications — robotics, toys, printers, cameras, medical devices, small machinery. They are not suitable for high-torque or high-speed applications where the lower strength and thermal conductivity of plastic compared with metal would cause rapid tooth wear or thermal failure. For high-torque applications at the same compact size, Korea Ever-Power recommends steel double spur gears or planetary gear stages. Contact Korea Ever-Power with your torque and speed requirements for correct gear selection.

"We build educational robot kits for schools and source ABS double spur gears (M1.5, DIN8) from Korea Ever-Power. The double gear eliminated one shaft pin from our robot joint assembly — reducing assembly time per joint from 4.2 to 2.8 minutes. Coaxiality between the two gear levels: measured < 0.03 mm runout across 100 pcs. Bidirectional torque test: same torque in both directions at 80% rated load — no measurable asymmetry. At our production volume of 25,000 robot kits/year, the part count saving is significant."

Kim Da-eun  |  Educational Robot Product Engineer, Incheon STEM Products Co.  ·  Q1 2026

"We produce laser printers and use POM M0.7 double spur gears (24T+52T, Delrin 500P) from Korea Ever-Power — the same specification as the printer double gear example on Korea Ever-Power's product page. Life test completed: 8 million feed cycles. Tooth thickness at 8M cycles: within 0.01 mm of initial measurement. Paper feed registration error at 8M cycles: unchanged from initial ±0.08 mm. Zero paper feed failures in our 18-month warranty period across 6,200 printers shipped."

Lee Jae-woo  |  Printer Mechanism Design Engineer, Gyeonggi Digital Systems Co.  ·  Q4 2025