What I Made
Every time I go somewhere where I need to spend the night I bring my toothbrush in a plastic bag. And every time a take a new bag to put my toothbrush in, I think to myself that this is very wasteful. So I descided to 3D print a case instead.
There a plenty of toothbrush cases online that you can just download and print, but beeing an engineer I felt the need to challange myself and over complicate this usually very simple design. Instead of having a top that screws on, or a case that splits in two, I wanted to make a case that spins to open. This gives a case that is always fully assembled so you can never lose a part (like a screw cap). It also makes it alot less likely for it to accidentaly open. Another benefit is that you can use the case as a toothbrush stand when it is not in you bag.
To make the case wall spin and lock in certain positions, I decided to design a ratchet mechanism that fits in the bottom of the case. This mechanism is connected to the inner wall of the case and the bottom lid. This way you can open the case by spinning the bottom lid while holding the outer wall.
I really wanted to print the whole case fully assembled. However, I could not figure out a way to do that and also having an easy way to hold the case to open it. This is because the ratchet mechanism is on the inside of the case, which means that the part connected to it has to wrap around the outside wall somehow. This in turn leads to the two parts needing to be printed on top of each other. This leads to the obvious challange of keeping the two parts from fusing together.
I did not manage to print the whole case in one part, but I managed two parts with a very simple assembly step. The only part that needs to be printed separatly is the bottom lid. It simly connects with a hexagon pin which can be glued to the rest of the case. It was challenging to get the rest of the case to print without fusing the two interlaced parts together. To get it to work I kept all distances between the parts at 0.5 mm. Since you can’t print horisontal lines in the air, I also made sure to design angles that the printer can handle without needing any support. This is shown in the top and bottom of the cross sectional view of the case.
One thing I want to note is how I made the curvature in the opening of the case. My first attempt of making a nice opening was done by having squared corners and then just adding fillets. This made a very ugly edge on the top part of the opening since it created a horisontal edge suspended in mid air. What I did instead was to create a sketch in the middle of the part. I then drew lines at 45 degrees and extruded them to cut both walls. I then just added a fillet on each side and I got this amazingly smoothly curved opening that is also extremely simple to print since it is virtually just a 45 degree slope. I will definetly use this technique again when I make cylindrical parts.
What I Think
This case is a good first version. It is not perfect however. I think the tolerances are too big so it feels a little loose and wiggly. I think this could be fixed by having very tight tolerances in certain places where the printer can handle it. I also think a big difference could be made by redesigning the ratchet. This ratchet is great for preventing movement in one direction. It does not however lock in tightly to a couple of positions. For this toothbrush case a spring that pushes a pin into a indent would probably do abetter job.
Redesigning the ratchet could also fix the other big problem with the case. It is just way too tall. It is around 5 cm taller than the toothbrush, which I thought would be fine when I designed it in CAD but seeing it in real life, that is just not the case. Since an electric toothbrush is thinner at the top where the brush is. The ratchet could be designed to fit inside of the wall at the top case, fitting around the toothbrush.
However, the biggest problem with the case is that the hexagonal pin holding the bottom lid to the case just keeps breaking. I have tried to make it as thick as possible, but I think the design is fundamentally weak and needs to be changed. This again, would be fixed by redisgning the ratchet.