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When a worn or undersized gear brings your CNC router, lathe, or automation rig to a halt, finding an exact-match replacement fast is everything. Machinists, robotics builders, and industrial maintenance teams rely on spur gears that hold tight tolerances under continuous load — and this range of 45# steel spur gears is engineered to deliver exactly that across a wide selection of modulus and tooth-count combinations.
Each gear is machined from 45# medium-carbon steel, offering a solid balance of hardness and toughness for power-transmission applications. The range covers Modulus 2.5, 3, 3.5, 4, and 5, with tooth counts from 10 to 70 teeth, yielding outer diameters from approximately 30 mm (1.18 in) up to 180 mm (7.09 in). Bore diameter and keyway dimensions vary by variant — see variant options for exact bore specs.
Typical use cases include CNC milling machine Z-axis drives, 3D printer extruder gearboxes, conveyor indexing systems, and DIY robotic arm joints — anywhere a reliable, off-the-shelf spur gear with a standard metric modulus is needed to replace or upgrade an existing drivetrain.
Machined from 45# carbon steel for a reliable combination of surface hardness and core toughness, suitable for moderate-to-heavy power transmission without brittle fracture risk.
Available in Modulus 2.5, 3, 3.5, 4, and 5 with 10–70 teeth per gear, covering outer diameters from ~30 mm to ~180 mm (1.18"–7.09") to suit a broad range of drivetrain ratios.
Cut to the industry-standard 20° pressure angle, ensuring smooth meshing with any mating gear of the same modulus — no custom tooling or special pairing required.
Spur (straight-cut) tooth geometry delivers efficient, low-noise power transfer on parallel shafts and simplifies alignment compared to helical alternatives.
Each gear features a machined central bore sized to accept a standard metric shaft. Keyway availability varies by modulus and tooth count — see variant options to confirm.
Designed for CNC machines, robotic arms, conveyor systems, 3D printer drives, and general mechanical power-transmission projects requiring a standard metric spur gear.
| Material | 45# Medium-Carbon Steel |
|---|---|
| Gear Type | Spur (Straight-Cut) |
| Pressure Angle | 20° |
| Available Modulus | 2.5 / 3 / 3.5 / 4 / 5 |
| Number of Teeth | 10 – 70 Teeth (see variant options) |
| Outer Diameter (OD) | Approx. 30 – 180 mm (1.18" – 7.09") — varies by modulus & tooth count |
| Bore Diameter | See variant options |
| Keyway | See variant options |
| Surface Finish | Machined (natural steel) |
| Application | CNC machines, robotics, conveyor drives, 3D printers, industrial gearboxes |
Modulus (M) defines the tooth size and must match between mating gears. Check the existing gear in your machine — the modulus is usually stamped on the hub or listed in the equipment manual. If you are designing from scratch, larger modulus gears (M4, M5) handle higher torque, while smaller modulus gears (M2.5, M3) suit lighter loads and tighter spaces.
Gear ratio = driven teeth ÷ driver teeth. For example, pairing a 20-tooth driver with a 40-tooth driven gear gives a 2:1 reduction. Select the tooth counts that achieve your target ratio while keeping both gears within the same modulus. Use the variant selector above to browse available combinations.
Yes — provided the mating gear shares the same modulus and pressure angle (20°). Spur gears of the same modulus mesh correctly regardless of tooth count. Always verify the bore diameter matches your shaft diameter before ordering, as bore sizes vary by variant.
45# carbon steel offers a tensile strength of approximately 600–800 MPa and is widely used in moderate-to-heavy industrial power transmission. For very high-shock or high-speed applications, consider whether a hardened or alloy steel gear would be more appropriate. For typical CNC, robotics, and conveyor use, 45# steel performs reliably.
Yes. Like all steel spur gears, these should be lubricated with a suitable gear grease or oil to reduce wear and heat. The lubrication interval depends on your operating speed, load, and environment. Enclosed gearboxes typically retain lubricant well; open drives may need more frequent re-greasing.
The outer diameter (OD) of a spur gear is calculated as OD = Modulus × (Number of Teeth + 2). For example, a M3 gear with 20 teeth has an OD of 3 × 22 = 66 mm (2.60"). Use this formula to verify the gear will fit your housing before ordering.
Absolutely. These spur gears are a popular choice for DIY CNC router axis drives, 3D printer extruder gearboxes, and custom robotic joints. Select the modulus and tooth count that matches your motor pinion and desired gear ratio, then confirm the bore fits your motor or lead-screw shaft.
