*UPDATED** V2 files.
I altered the design so the top part prints flat. The bottom is still domed as described below. Carefully use pliers to snap the tabs into the slot if they don't easily piece together with your fingers.
When snapping the parts together, be sure to align the fins parallel with the slots cut through the bottom piece. The fins will fit into the slots when everything is seated properly. You will likely have to put a little pressure onto each fin to get them seated into their respective slots.
The easiest way to join the parts is to move the top part off center from the bottom... the tabs are tapered so it should slide in if you align the narrower part of the tab over its slot. Once in, push the edge down on a hard flat surface to flush the two parts' edges up. Then use your pliers to snap in the other three tabs. I was able to do this with my fingers but pliers are helpful. Just be careful each tab is lined up in the slot before you go squeezing it with pliers.
This is my Ultimate Drink Coaster design. Why is this better then every other coaster on this site? Here are the features:
1) Over-sized. At about 5" diameter, this will hold your largest beer stein, bottle of whatever, your novelty coffee mug, just about anything drinkable.
2) This will not stick to your glass when you pick it up. Radiused fins break the suction of condensation. Not a new idea, but a feature nonetheless.
3) Two piece design. Not only is this stylish (print parts in two colors for added awesomeness - impress your family and friends), but it simplifies the printing and allows what would be an impossible print if a solid piece.
4) Bottom piece collects condensation that gathers on your glass. There is a collection moat around the outside. The center is domed to allow the condensation (or your accidental spill) to run down the sides of the dome and collect in the moat.
5) There are weep holes in the top part that are cut through all the fins (see cross section image). The weep holes allow the water to wick through the fins, down the domed center, and into the moat.
6) simple assembly. Print the two parts. tab and slot design allows the two parts to snap together. No glue or screws needed. Disassemble for easy cleaning.
Ok, so I have tested this coaster. Works fantastically. It will suck up a lot of liquid before it fills up. Your drink will no longer simmer in a pool of condensation while you pound beers in your humid garage.
Printing: The bottom part prints fine with no support. The top part is shaped in the center on the underside of the fins to accommodate the domed portion of the bottom piece. On my printer, it didn't like printing without support. It didn't add much... just a few layers, but it was necessary. I plan to correct this so the top part prints flat too. Maybe this weekend. But for now, no worries. Add support for the top. 80 degrees overhang. You don't want it adding support and filling up the weep holes. Each part took about 3-4 hours. The bottom you can print at 0.2mm and speed it along. I would narrow it up for the top so you get good resolution for the fins and weep holes. I recommend 0.1mm. I printed with PLA.
Would love to see some makes if you like my design and print it. I download a lot from this site and enjoy adding back to the community. Let me know if you have any other suggestions.