These parts like to warp in ABS. They are meant to be printed with 100% infill for maximum strength as they will hold a 16" long x10" diametrer cylinder of coroplast sheets, about two full 4x8 ft x 4mm thick sheets. I took the suggestion of using ABS Glue - ABS + Acetone and painting over blue painters tape. That works great but Kapton is even better -- but it sticks too good and is harder to replace.
ABS glue is great for anti-warping but a nightmare to remove once done!
The honeycombs are used to accommodate the thickness of the sheet-holding clips to prevent air spillage between the hot and cold side of the thermal wheel. You will need to reference my Hackaday.io project to get the details on the Coroplast cutting. See my other Things for a Coroplast cutting tool. Another tool for cutting 16" cross-grain strips is in the works.
To make a full cylinder assembly, you need a Honeycomb Bearing Hub for the passive end and a Honeycomb Bearing Pulley Hub for the driven end. You need a total of 4x HE_Clip_Single_Rank_HC3 and 4x HC4 parts, 4x Honeycomb_HC3 and 4x Honeycomb HC4, and 4x Honeycomb_HC2 pieces. For the cutout Coroplast parts, two 4x8ft x 4mm Coroplast corrugated plastic from Home Depot (online). Note minimum order is 10 sheets @ $11 each.
Design of the heat exchanger is unfinished and untested, so I wouldn't rush out just yet...
The honeycomb functions may be useful for other things you might want to build. You just need to make the walls thick enough the slicer won't delete them.
Skate bearings press into the sockets on each end. A frame assembly to mate with the hub bearings is in the works.