I wanted to see if I could get a serviceable truck for my 3D printed HO scale freight cars, and this print seems to work quite nicely. I printed them with an 0.25 nozzle at a layer height of 0.05 for ultrafine detailing, printed with no supports. A set of 4 takes a little over 4 hours to print at those settings.

Edit: Printed out a set at 0.10 layer and they turn out excellent, with no noticeable difference in quality, and half the print time.

There is a 26mm version and a 24mm version, depending on what your source is for wheelsets one may work better than the other. I am using the #523 Kadee code 110 33" freight wheels and the 26mm size seems to be right for that axle. For now I have just the two, but I will likely remix several versions stepped by the half millimeter and upload them when I get a chance, so you can decide which version you like best for your stock and axles.

The center bore is set up for a 2mm machine screw and the cross-member has a flat back, so if you were to use these on commercially available rolling stock with the raised shoulder where the bogie mounts, you'd likely want to remix it with a cup to mate with that detail. That or slice off the shoulders from the undercarriage. 

So, with these and the cars I mixed (see my other prints), I can print out a complete piece of rolling stock minus wheelsets and couplers, which I prefer not to mess with.

If I get bored I'll mix in the third spring, but for now they are modeled on a heavy duty spring made of futuristic materials that only requires two per truck per side. ;-)

Edit 3-10-22: added a new version ("Bogie26-9 ConeV2") with an improved axle cone and a slightly wider point-to-point axle span of 26.9mm. The Bogie26 was a little snug and didn't free-roll with the #523 Kadee wheel sets. This size seems perfect for that axle.

Also swapped out “Bogie26” for “Bogie26-4 ConeV2”, also with the better cone, and to accurately reflect the 26.4mm point-to-point dimension.