Don't know much about 3.5" gauge steam items (or anything else for that matter) but like your work so far. I was surprised by the square shoulder and small depth of the flanges - thought they would have needed to be deeper and/or tapered to track correctly but apparently not. And impressed by the truck sideframes which must have taken quite a bit of time to cut - they look good!
Thanks for your observations. I thought about these same topics when I was planning the wheel, especially since I have had no training whatever in machining.
Shoulder, flanges, and everything else follow a 1945 flat car plan I found on the web. I, too, wondered about the shoulder, but the general opinion seems to be that coning the wheels is more significant for tracking. The design I used did not call for coned wheels, but I cut a 3 degree taper there, though it's hard to see over a 3/8" tread. Moreover, the track on which this is to be run is not one of those snazzy factory-made rail things, but 3/8" x 1" mild steel bar set on edge, and I think that the square shoulder will work better with it (there is a teensy little radius there to preserve strength). Flange depth may be a consideration if the car is to travel over frogs, points, etc., but my track is a simple oval, and I just don't see a wheel hopping up and down.
As you can see, I arrived at the wheel profile after a lot of mulling and reading, and I like to think that I've done the right thing here. Of course, if I haven't, I'll find out in May when I run this car. Even then, though, it won't be all that hard to re-shape the wheels if I have to (I hope).
As for the side frames, they will do the job, but I messed up on the symmetry of the outlines. It's not too easy to see when the frames are under the car, but trust me, they could be a lot better. I didn't re-do them both because they're hard to see and because they really did take a lot of time to make.