Making a Freight Car Bogey

Note: I use Blender so some names maybe defendant for other 3D programs.

I start out with a 32 segment cylinder the size of the Journal box, extrude the top half up to the top of the frame, delete 3 sets of vertices, and move some as shown in Fig1.  

Fig1

Next I extrude the 4 vertices on the right side of Fig1 to that in Fig2, I have also added a set of vertices to the bottom so that all the hole is covered. This is then separated and a face is added so that this is now a solid object. This is going to have a Boolean hole cut into it and the Boolean tool works on volume so the simpler the object the better. 

Fig2

Next up is the hole witch is made also from a 32 segment cylinder. In this case 3 of the 4 curves are the same size so I move them into place and make the object wider than the one just made. It looks like Fig3.

Fig3

The Boolean should look like Fig.4

Fig4

After the hole is cut out I add some more vertices to the bottom and extrude the 4 vertices on the right side and do the same as above but with a square hole, Fig5.

Fig5

I then select the black part of Fig5 and duplicate it, mirror it, move it , and do a flip normals on it. Last is to join all the parts into one, remove extra faces, and smooth the round parts(not done for this yet) giving you Fig6.

Fig6