I have a delightful three year old in my life (full disclosure: I'm pretty sure I'm his dad) who just loves the shit out of his wooden train tracks, as well as his collection of legos and duplos. So, for Christmas, I asked myself: What could be better than having the living room covered in a mess of all three of these kinds of toys at once?
Sliced using slic3r with default settings for 0.15mm layer thickness and supports from the bed. Printed on a Prusa i3 mk3 with MatterHackers build filament.
The duplo and lego interfaces on these parts are not exactly to specification due to some dimensional differences when printed. I found these value experimentally, but they may not be ideal if you're using a different printer.
Some assembly required: I used some brass furniture tacks for the axle hubs and magnet caps, the latter after breaking the pins off. The front and rear of the train bodies accept two 8x3mm magnets - I recommend ceramic. The caps are then glued on top to hold them in. I used Precision Metals #8126 for the axles, cut to 30mm (using the saw guide included here) and soldered/brazed onto the aforementioned tacks, though epoxy or glue might work as well.
The axle slots in the train body may need to be filed a little prior to pressing the axles in.
I will be adding photos and parameterization as time permits.