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When a loose or undersized gear causes missed steps, vibration, or premature wear in your motion-control build, the root cause is almost always a mismatch between gear modulus, bore size, and shaft tolerance. Makers, engineers, and small-batch manufacturers who run CNC routers, 3D printer extruder drives, or robotic arm joints need a spur gear that holds tight tolerances without requiring custom machining.
These 1.5 module, 25-tooth spur gears are machined from 45# medium-carbon steel — a material known for its balanced hardness and machinability. Each gear features a face width (teeth thickness) of either 12 mm (~0.47 in) or 15 mm (~0.59 in), with bore options ranging from 6 mm to 20 mm (~0.24–0.79 in). Select variants include a precision keyway (3×1.4 mm, 4×1.8 mm, or 5×2.3 mm) for positive torque transmission without set-screw slip.
Typical applications include stepper motor pinion drives in CNC plasma tables and laser engravers, rack-and-pinion linear actuators for automated sliding gates, and reduction gear stages in robotic arm elbow joints where a 1.5 mod pitch line keeps backlash under control.
Machined from 45# carbon steel for a tensile strength typically in the 600–800 MPa range, giving the gear tooth flanks the hardness needed to resist pitting and wear under sustained cyclic loads.
A 1.5 mod pitch delivers a tooth height of approximately 3.375 mm and a pitch circle diameter of 37.5 mm, making this gear a direct drop-in for standard Mod 1.5 racks and mating gears without custom modification.
Bore options from 6 mm to 20 mm cover the most common stepper and servo motor shaft diameters. Keyway variants (3×1.4 mm, 4×1.8 mm, 5×2.3 mm) lock the gear to the shaft for zero rotational slip under reversing loads.
The 12 mm face width suits compact drive trains where axial space is limited; the 15 mm face width increases the load-bearing contact area for higher-torque applications such as rack-and-pinion actuators.
Hobbed tooth profiles maintain consistent involute geometry across the full face width, keeping backlash predictable and minimising positioning error in open-loop stepper motor systems.
Bores are finished to an H7 tolerance class (See variant options for exact fit), allowing a light press or slip fit onto standard motor shafts. No additional boring or reaming required for most common shaft diameters.
| Module (Mod) | 1.5 |
|---|---|
| Number of Teeth | 25 |
| Pitch Circle Diameter | 37.5 mm (1.476 in) |
| Tooth Height (Addendum + Dedendum) | ~3.375 mm (~0.133 in) |
| Face Width (Teeth Thickness) | 12 mm (0.47 in) or 15 mm (0.59 in) — See variant options |
| Bore Diameter | 6 mm – 20 mm (0.24 – 0.79 in) — See variant options |
| Keyway | None (plain bore) or 3×1.4 mm / 4×1.8 mm / 5×2.3 mm — See variant options |
| Material | 45# Medium-Carbon Steel |
| Surface Finish | Natural / Lightly Oiled |
| Pressure Angle | 20° |
| Gear Type | External Spur Gear (Pinion) |
| Compatible Rack / Gear Module | Mod 1.5 |
| Weight | See variant options |
The face width (teeth thickness) directly affects the load capacity of the gear. If your application involves light-duty positioning — such as a 3D printer extruder or a small CNC axis — the 12 mm face width is sufficient and saves axial space. For higher-torque applications like rack-and-pinion linear actuators or robotic joints carrying meaningful loads, the 15 mm face width provides a larger contact area and distributes stress more evenly across the tooth flank.
Match the bore to your motor shaft diameter. Common NEMA 17 stepper motors use a 5 mm shaft — in that case, select the 6 mm bore (smallest available) and use a 5-to-6 mm shaft adapter, or choose a variant closest to your shaft OD. NEMA 23 motors typically use 6.35 mm (1/4 in) or 8 mm shafts. For shafts requiring positive torque lock, choose a keyway variant whose keyway dimensions match your shaft's key slot.
45# carbon steel has a typical tensile strength of 600–800 MPa and yield strength around 355–490 MPa in the normalised condition. This is adequate for the majority of CNC, robotics, and automation drive applications at moderate speeds and loads. If your application involves continuous high-speed operation under heavy load, consider whether a hardened or alloy steel gear would be more appropriate for your specific duty cycle.
45# carbon steel is not inherently corrosion-resistant. For indoor, dry environments — typical of CNC machines and robotics — the lightly oiled surface finish provides short-term protection during storage and initial use. For humid or outdoor environments, apply a light machine oil or grease to the tooth flanks and bore regularly, or consider a zinc-plated or stainless alternative if corrosion is a primary concern.
Yes. This 25-tooth, 1.5 module spur gear meshes directly with any standard Mod 1.5 rack. With 25 teeth and a 1.5 module, one full rotation of the gear advances the rack by 25 × π × 1.5 mm ≈ 117.8 mm of linear travel. This makes it straightforward to calculate steps-per-mm for stepper motor control in CNC or automation applications.
A plain bore relies on a set screw or interference fit to transmit torque from the shaft to the gear. This is adequate for light-duty or unidirectional loads. A keyway bore uses a machined slot that accepts a matching key on the shaft, creating a positive mechanical lock. Keyway variants are recommended for reversing loads, higher torques, or any application where set-screw loosening under vibration is a concern.
For two spur gears to mesh correctly, they must share the same module (Mod 1.5 in this case) and the same pressure angle (20°). The centre distance between the two gear shafts should equal half the sum of their pitch circle diameters: (PCD₁ + PCD₂) / 2. For this 25-tooth gear, PCD = 37.5 mm, so pair it with a mating gear whose PCD you know to calculate the required shaft centre distance.
