Push me - Pull me Door Catch
There is a door in my house that is "finely balanced" on it's hinges. So finely balanced that simply walking past it at a pace other than snails caused it to swing closed. This door tends to remain open at all times unless I have to keep little kids out of MY play room :)
So to keep the door open most of the time but to retain the easy option to close it sparked some ideas in my head. I camped/caravan'ed a lot as a child (and still do to be honest) and so the idea of a simple push/pull door catch like those on the back of caravan doors to hold them open was obviously near the front of my brain.
The simplest design I could think of was a "ball and cup" socket. Something that could be pushed into the socket with a small force but still be easily releasable by pulling. No moving parts to fail, simple wear and tear to think of. I tend to print in ABS which is slightly flexible if not printed too thick. This meant that with a little trial and error I could find out a reasonable thickness the socket needs to be so it is strong and gives a bit of resistance to the ball part of the socket but not so much that it needs to be slammed loudly.
The opening to the cup part of the socket was and still is a 90 degree angle from the centre of the cup. I think I just got lucky with this idea as it worked beautifully first time and hasn't needed any tweaking at all.
The final consideration was the offset from the wall. The two halfs to the catch when pushed together will need to be long enough so that the door handle doesn't hit the wall. Simple maths sorted that out with a little room for error. As the model was designed in OpenSCAD, I deliberately made the catch design parametric so details like that could be tweaked easily and re-printed to requirements.
The design has been in daily use since at least June 2015 and pretty much every door in my house now has one of these catches printed and screwed in place. Very helpful when you need to keep your childs door open at night with the windows open for airflow. No loud noises of doors slamming closed in the wind to wake anyone up is most definitely appreciated!
Obviously I should cover my rear and say please don't use these on fire doors (or any other doors) that should remain closed at all times.