Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2749150.
NOTE: I make no claim or warranty about the safety or stability of these under the bearing of any load. You do so at your own risk.
I had bought this UTAKER bed from Ikea: http://www.ikea.com/us/en/catalog/products/30360487/
Turns out the mattresses they displayed with it were about an inch too tall for the beds to properly stack, so I made these risers to fit between the beds to accommodate the added mattress heights. They have a side with a hole for the top beds peg to fit into, and a peg on the opposite side to fit into the bottom bed's hole for stability. I also gave them the same curvature as the bed legs to blend in ascetically. They give a 1.5" rise so you can comfortably accommodate a 6" mattress instead of a 5" mattress when stacked.
I printed them with 65% infill because I was paranoid about the sturdiness and support in case someone accidentally sat or jumped onto the stacked beds while I had the risers in there.