Nov 29, 2015

3D Printed "House of Cards" Stackers

With all the travel I do, I have lots of leftover hotel room keys - the credit card looking type.
I thought it would be fun to design a 3D printed connector which let my kids build stuff using those cards - basically, a house of cards which doesn't fall when you breathe on it ;)

Design Testing First

I started with the simplest, but most important part of the design - the holder which connects to the card.

This is basically a simple slot - a gap between two plastic parts which needed to be just the right tightness to hold the card firmly, while not being too tight or so narrow that the 3D printer has a hard time leaving the space during the printing process.

The simplest test part was step 1 - just creating a block with different sized gaps along the z-axis (vertically upward from the print bed). I didn't bother trying to create gaps on the horizontal plane, assuming that the slightest sag in the filament during printing would fill the gap and make it useless.

Tweaking the design to actually work

After a bit of experimentation, it seemed my Polar3D provided a firm hold on a card with a 1.0mm gap. On my LulzBot TAZ4, the gap was slightly smaller but also didn't give me as consistent a fit with the squashed first layer closing the gap too often. I could have fixed this with re-calibration I assume, but didn't try.

Once I had a simple block that worked, I tried out a few on some key cards, and found that they were simply too easily popped off as I was building. I adjusted the design as a solution to this - basically putting two blocks at opposite ends of a stick with the gaps facing inward so the holder fit over the card like a strap. This worked incredibly well.

Final design and Printing

Once I had that basic "strap" design working, I added an whole set of additional gripper slots facing in all 4 directions as well as on top of the end blocks. This combination proved to be the best and I stopped there and printed a dozen or so of these to test the building.

Building Fun!

I was able to easily build a single column square block of cards about 8 cards high which was very sturdy. The card-grippers print very quickly, as they are made of very little material - probably taking about 8 minutes each at a resolution of 0.2mm. I have yet to break one either since most of the connectors are along the horizontal plane, giving it more strength.

The Model

I've uploaded the basic model to PinShape so
you can try these yourself. It's actually really fun to try printing them in different configurations to meet the specific needs of a house of cards you want to design.

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