Designing and building is something of a hobby of mine that also happens to be a component of my profession. I like to flex my CAD muscle outside of the professional setting whenever possible so if someone tells me about a need for something and the design and 3D printing of it is within my bandwidth of available time, I like to help them out. Because… why not?
Demand Signal
A buddy of mine was telling me how he wanted to add a 2 inch by 2 inch card holder for a small sign to advertise his Tour Services. He kicked around an idea of what he wanted: to hold business cards on a placard but didn’t have an immediate solution in mind. So I offered to help out.
Design process
I took a card measured it and made the holder as such that it wouldn’t cover up any of the information on the card. I printed it off and evaluated how the cards fit on the initial design but wasn’t happy with it .

There was too much slop, side to side, so retaining the cards could get all catty wampus and potentially fall out. I determined that falling out was an unacceptable failure mode. A card holder must hold the card. I tightened up the space between the walls and the card by a few millimeters and it felt purposefully correct. The final design is available on Thingiverse for you to download and see if it can potentially fit one of your needs.
I initially designed this using PTC Creo but since I am making a point to do more design work on Linux, specifically openSUSE Linux, have since recreated it using FreeCAD with a little variation. Feel free to download the STEP or FreeCAD file and modify it to your heart’s content.
The only real difference between the two designs is that one has sides that are open and the other is solid. The solid sides do print better. I suppose could have added some other flair to it but seeing how this part is not the focus of the placard, why bother.
Final Thoughts
CAD is a fun problem solving tool, once you know how to use it. The fact that there is FreeCAD on Linux, which is a pretty decent tool opens up a whole world of problem solving for the masses. Having a resource like Thingiverse to share how you have solved problems makes these times we live in a lot of fun.