D&RG 3' 7" Caboose Truck
UPDATE:
Better springs that work well with this design are here: https://www.thingiverse.com/thing:4082130
Springs work well in ABS and PETG, PLA is too stiff.
Two spring pieces should be connected at the tip with a 1/16" wire to stabilize them in the truck.
PETG will need lubrication at the sliding joints, otherwise it sticks badly.
I recommend using brass tube or miniature ball bearings in the journals. I'm testing using the ABS as the bearings with some plastic-safe oil but the other options should produce lower friction and longer wear, not to mention being easily replaceable.