NEMA 14 Planetary gear Ratio 1:4 - V1

Planetary Gearbox for NEMA 14 Motors

This planetary gearbox was designed for a real-world use case with a NEMA 14 stepper motor. Most existing designs online are optimized for NEMA 17, so I created a dedicated solution specifically for NEMA 14.

The goal was to reduce speed, smooth out rotation, and increase usable torque. In my original setup, the NEMA 14 struggled to rotate an out-of-balance 100 g load, resulting in twitchy and inconsistent motion. With this gearbox, the motor now runs smoothly and reliably.

Aimed at 1:3 ratio but 1:4 gear ratio turned out to be the perfect balance for my project — higher ratios (1:5 and above) were unnecessary.

Gear Specifications

• Outer Ring Gear: 36 teeth

• Sun Gear: 12 teeth

• Planetary Gears: 12 teeth

• Backlash: 0.12

• Root Fillet Radius: 0.35

Available Versions

Use whichever version fits your needs:

1. Central axis with bearing (CURRENT VERSION – recommended)*

2. Version without bearing (earlier version, useful for testing)**

*The bearing absorbs the radial force from the belt, keeping the output axle firmly aligned in the center and significantly reducing — or almost eliminating — distortion under load.

**No bearing, carrier has some distance thus radial movements under load could be used for gears, but not best for belt.

Parts Used

• Bearing:

  • 688-2RS ZEN

  • Dimensions: 8 mm inner / 16 mm outer / 5 mm thickness

  • Any bearing with the same dimensions will work

• Screws:

  • 4× M3 × 20 mm – for standalone motor use

  • 4× M3 × 30 mm – when mounting the motor to another project

• Overall thickness:

  • All printed layers add up to 17 mm, plus 3 mm motor hole depth for M3 screws

Printing Recommendations

• Material: PETG (used for all parts)

• Infill: 60% recommended (30–60% works fine)

• Orientation: Optimized to minimize supports

• Lubrication:

  • Use plastic-safe grease on gears and all moving contact surfaces (strongly recommended)

Assembly Instructions

1. Mount the First Layer part onto the motor.

   • You should end up with a flat surface and the motor shaft protruding.

2. Press one small gear (sun gear) onto the motor shaft.

   • Tight fit is intended; glue is optional (I didn’t glue mine).

3. Install the Gear Ring.

4. Assemble the Carrier Bottom under the Carrier.

   • Lightly sand the bottom disk to make it flatter and smoother.

   • I glued the bottom disk to the carrier to reduce noise — optional, but recommended.

5. Optional: Apply plastic-safe grease before continuing.

6. Mount the remaining planetary gears onto the carrier pins.

   • Carefully slide the entire assembly over the motor shaft.

   • This is the trickiest step — take your time.

7. TEST rotation gently.

8. Install the Top Cover over the carrier.

9. Final mounting:

   • If mounting to another object (e.g. I used 9 mm PETG), use M3 × 30 mm screws.

   • Hold the gearbox assembly in place while tightening.

   • For standalone use, use M3 × 20 mm screws to clamp everything together.

⚠ DO NOT OVER-TIGHTEN THE SCREWS.

Important Notes

• The first image shows two gearbox versions:

  • Bottom parts = newer, stronger version with bearing

  • Images with a pulley = new version, fully assembled

  • The last image shows the older version, demonstrating the smoothing / locking disk

• The smoothing disk is used to prevent the carrier from pressing down and locking the gears.

  • Gears are 4 mm thick, while the gear ring is 5 mm thick