For a video, see https://www.youtube.com/watch?v=UKDRf53VEHc.
This wallet will hold up to 6 cards, but works with less cards as well.
I have used it for about a month now and for me it is really an improvement over my old bulky leather wallet.
No need for 'friction patches' or anything to keep the cards from falling out, the compliant mechanism on the back makes sure of that. Just don't shake it too hard!
Press the lever on the bottom in a downward motion to make the cards pop out.
Caution!: Edges can be sharp, even though a fillet has been applied to them. Use sandpaper if the edges are sharp (I only sanded one edge of the turning thingy).
STL files are in the right orientation for printing, no supports needed.
Printed in PLA, with 0.1 mm layer height.
I used 10% infill for the frontside and turn-thingy and 100% for the backside, but 10% might also be ok.
No need for glue.
First place the turning thingy on the 'cylinder' of the backside part.
Then slide the front side on the backside part until it clicks.
Edit: As was pointed out in the comments, some cards in other countries might have slightly different dimensions. This cardholder was designed for cards that are 54 x 85 mm and has a 1 mm margin. If your cards have different dimensions, then you can scale the STLs accordingly. If this scaling is not done uniformly, then it is possible that it will not work anymore because the turning-thingy cannot turn on an oval cylinder.
Use sandpaper on the edges if they are sharp.