14.2:1 Gearbox

Functional prototype gearbox with a 14.2:1 reduction ratio.

This project is a prototype gearbox for an electric 35 mm film rewinder. The goal was to design a new drive system with speed control and soft start, without modifying the original construction of the rewinder.

The gearbox is designed as a standalone 3D printed assembly. It consists of a main stand, front and rear side panels, a third gear holder, a cover, and a cover lid. The transmission uses a combination of gears and pulleys. The first and second transmission stages combine a gear with a V-belt pulley, while the third gear works as an additional reduction stage. The individual parts are secured with clamping screws and spacing washers.

The purpose of the gearbox is to reduce the high motor speed to a more suitable speed. In this prototype, the transmission reduces the speed from approximately 5500 rpm to 390 rpm at the film reel, which gives a reduction ratio of about 14.2:1. Further speed control is handled by an electronic motor controller.

The structural parts are designed to be printed from PC-CF for stiffness and durability. The gears are designed to be printed from PA12 due to its better properties under mechanical load. The gearbox is intended for FDM 3D printing, and the gears should be lubricated with a suitable synthetic grease.

The prototype was printed, assembled, and tested in the actual device. The gearbox itself worked, but the test showed that the motor used in this setup was too weak under higher load. For that reason, this project mainly served as a proof of concept and as a starting point for further development of the drive system.

I am sharing this model as inspiration and as a starting point for further modifications or similar projects.

Printed materials:

PC-CF, PA12

Additional required parts:

Hex head bolt with partial thread M8×65 – 1×

Hex head bolt with partial thread M8×75 – 2×

Spacing washer M8×1 – approx. 20×

M8 nut – 3×

608 ZZ bearing – 5×

M3×8 screw – 11×