The door handle and lock mechanism in my recently installed new inner doors proved to be squeaky and very low quality. So I set out to design my own for 3D printing.
I unscrewed a door lock and opened it op to study how the inner workings were designed. I wanted to see why the locks made so much noise when moving the door handle, but quickly understood that the reason was poor design and low quality. The case was made of thin metal plates and the springs inside had almost no guiding or good fit. All moving parts were sliding against other surfaces without any means of bearings or (well designed) guided tracks. As an assembly it was basically a metal rattling box.
Looking at the parts inside I found the mechanism intriguing and started designing in Autodesk Fusion 360.
I designed several quick iterations that could quickly be printed while I modified the design over and over again as I tested out movements and parts fit.
This was truly I fun design experience as I bit by bit understood the structural integrity of the case and the loads on the inner moving parts affected the overall design.
I decided to use ball bearings for the rotating parts for optimal movement and low sound. I used ball bearings with an inner diameter of 17mm making space for the square door handle steel rod.
The springs I used was from a Biltema spring assortment kit and I had to test several different types to decide which would work. However I have already experienced that these springs will make a squeaky sound sometimes! Possibly due to the spring having a design where the steel is in contact with itself in each end. I need to investigate a type of spring that is completely silent.
Design in progress. Article will be updated as I progress the design.
FunctionalDesign 