Project information

Title : 3D printing a replacement cog for a rotary fan heater

Date : 21/03/2026

Description : I repaired a cheap rotary fan heater by reinforcing the original motor and measuring, 3D modelling and 3D printing a new cog

Problem : A single rib of the original cog broke off which caused the turning mechanism to fail.

Overview

One of my fan heaters broke due to a cog which lost one of it's ribs. I pulled it apart and inspected the inside of the heater and inside of the rotary motor.

I found that the rotary motor was designed to change direction when a considerable amount of force is met, this explains why only a motor was needed and also how the heater changes direction.

I designed a cog by taking measurements of the broken cog with a caliper, I used blender to create the 3D model. Initially I printed a prototype with PLA, this whe used proved that the cog worked but as it was made of PLA and a sparse infill it eventually failed and deformed.

Upon inspecting the motor I found cracks in the metal body, seeing this I used a hose clamp to reinforce the housing.

I printed a new cog with nylon which was entirely solid, I then tested this cog in the heater for multiple hours before concluding it a sucess.

The heater itself is not of high quality and some of it's plastic has been damaged, the original cog itself broke a rib, I suspect that the printed cog I made or even some kind of other part may brake in the future, I suspect that the motor's turning force requirement is too high.

PS. Unfortunately I don't have an image of the original cog as I gave it to someone else who was going to try and print it when I didn't have my own 3D printer.