Mod 3/4/5 Spur Gear Pinion Gear 10T - 100T Motor Pinion 45# Steel Hardening

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Mod 3/4/5 Spur Gear Pinion Gear 10T - 100T Motor Pinion 45# Steel Hardening

HomeDIYer

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Tooth: 3M 10T

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$9.10 USD

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In stock (500 units), ready to be shipped

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Mod 3/4/5 Spur Gear Pinion Gear — Precision 45# Steel for DIY Automation & CNC Drives

When a stripped or undersized pinion gear stalls your CNC router, robot arm, or motorized axis mid-project, the entire build grinds to a halt. Makers, workshop engineers, and automation hobbyists need a pinion gear that holds its tooth profile under real load — not one that wears out after a few hundred cycles. These Mod 3/4/5 spur gear pinion gears are machined from 45# carbon steel and heat-treated to deliver consistent, repeatable mesh engagement across a wide range of drive applications.

Each pinion gear is cut to a specific module (Mod 3, Mod 4, or Mod 5) and tooth count (10T through 100T, depending on pitch), with a bore diameter that varies by variant — typically ranging from approximately 5 mm to 25 mm (0.20" to 0.98"). The gear face width and outer diameter scale proportionally with module and tooth count. The 45# steel substrate is hardened to improve surface wear resistance while retaining enough core toughness to absorb shock loads common in motor-driven pinion applications.

Typical use cases include motor pinion drives on CNC gantry systems requiring a mod 5 spur gear for high-torque rack-and-pinion setups, small robotics joints using a mod 3 pinion gear for compact tooth engagement, and DIY automation conveyor drives where a mod 4 steel pinion gear replaces a worn plastic or aluminum original. The broad tooth count range — from 10T for high-speed small-diameter pinions to 100T for large reduction stages — makes this series a practical single-source solution for multi-stage gearbox prototyping.

⚙️ Compatibility: Meshes with any standard Mod 3, Mod 4, or Mod 5 spur gear or rack of matching module. Bore diameter varies by variant — confirm your motor shaft diameter before ordering.

✅ Key Features of These Mod 3/4/5 Spur Gear Pinion Gears

🔩 45# Carbon Steel Construction

Machined from 45# medium-carbon steel — a widely used engineering grade known for its balance of machinability, tensile strength, and response to heat treatment.

🔥 Hardening Treatment Applied

Each gear undergoes a hardening process to increase tooth surface hardness, extending service life under repetitive mesh contact and moderate shock loading.

📐 Three Module Options: Mod 3, 4 & 5

Select the module that matches your existing rack, gear, or gearbox. Mod 3 suits compact drives; Mod 4 balances size and torque; Mod 5 handles heavier loads.

🔢 Wide Tooth Count Range: 10T – 100T

From small high-speed pinions at 10 teeth to large reduction-stage gears at 100 teeth, this series covers the most common DIY and light-industrial tooth count requirements.

🎯 Precision-Cut Tooth Profile

Involute tooth geometry is machined to standard module tolerances, ensuring smooth mesh engagement and minimal backlash when paired with a correctly matched gear or rack.

🛠️ Direct Motor Shaft Mounting

Designed as a motor pinion gear with a through-bore for direct shaft mounting. Confirm bore diameter from the variant detail before installation on your motor or drive shaft.

📐 Technical Specifications — Mod 3/4/5 Spur Gear Pinion

Material	45# Carbon Steel
Surface Treatment	Hardening (heat treatment)
Module Options	Mod 3, Mod 4, Mod 5
Tooth Count Range	10T – 100T (varies by module)
Tooth Profile	Standard involute spur gear
Pressure Angle	20°
Bore Diameter	See variant options
Outer Diameter	See variant options
Face Width	See variant options
Keyway / Set Screw	See variant options
Finish	Natural steel / oxide
Application	Motor pinion, CNC drive, robotics, automation

❓ Frequently Asked Questions

How do I choose between Mod 3, Mod 4, and Mod 5?

The module must match the gear or rack it will mesh with — you cannot mix modules. Mod 3 is suited to compact, lower-torque drives where space is limited. Mod 4 is a common mid-range choice for CNC gantries and light automation. Mod 5 is used where higher torque transmission or larger center distances are required. Check your existing gear or rack specification before selecting.

What tooth count should I select for my motor pinion application?

Tooth count determines your gear ratio when paired with a driven gear. A lower tooth count (e.g., 10T–15T) on the pinion produces a higher reduction ratio and is typical for motor output shafts driving larger gears. A higher tooth count pinion reduces the ratio and is used when less speed reduction is needed. Calculate your required ratio first, then select the pinion tooth count accordingly.

How hard is the gear after the hardening treatment?

45# steel responds well to heat treatment. After hardening, the tooth surface hardness is typically in the range of 45–55 HRC depending on the specific process applied, while the core retains toughness to resist fracture under shock loads. This makes it suitable for moderate-duty motor pinion and automation drive applications. For very high-cycle or heavy industrial loads, consult us to confirm suitability.

Is this gear corrosion resistant?

45# carbon steel has limited inherent corrosion resistance. For indoor, dry, or lightly oiled environments — typical of CNC machines, robotics enclosures, and workshop automation — the gear will perform well with standard lubrication. For outdoor or high-humidity environments, consider applying a light grease or protective coating after installation. If corrosion resistance is a primary requirement, contact us to discuss alternative material options.

Will this pinion gear fit my motor shaft directly?

The bore diameter varies by variant (module and tooth count). Before ordering, check the bore diameter listed in the variant detail and compare it to your motor shaft diameter. If the bore is larger than your shaft, a set screw or keyway (where present) can be used to secure it. If the bore is smaller than your shaft, this gear will not fit without machining. Always confirm bore dimensions before purchase.

Can I use this gear with a rack-and-pinion system?

Yes. These spur gear pinions are compatible with standard module racks of the same module (Mod 3, 4, or 5). This makes them a common choice for CNC router gantry drives, linear actuator systems, and motorized axis builds. Ensure the rack module matches the pinion module exactly for correct tooth engagement and minimal backlash.

What is the difference between a spur gear and a helical gear for this application?

Spur gears like these have straight teeth parallel to the gear axis, which makes them straightforward to install and align, and they transmit power efficiently without generating axial thrust forces. Helical gears have angled teeth that engage more gradually, producing quieter operation and higher load capacity, but they require thrust bearings to handle axial loads. For most DIY CNC, robotics, and automation pinion applications, spur gears are the practical and cost-effective choice.

🛒 Select your Tooth (module and tooth count) above, then add to cart.