You asked about 'Joining' the surfaces of the cylinder model. As I said, the model shown was just to look at. One thing that I did in that regard was to make curves of all the edges that I want to be seen as edges; then I gave them a different color. This looks much better than otherwise. Of course you want to hide all the edges of surfaces that should look continuous. But when you hide the edges, the edges that should look like edges become sort of fuzzy. To change the model for 3D printing, I eliminated all those curves, so that I had only surfaces. I also eliminated all the 'holes' (screw holes) which were open on the bottom. I then 'Joined' the surfaces. Only one had a problem! Think about that: More than 1400 surfaces in this model and only one problem. That surface was a simple one and I redid it in a few seconds. Then the whole cylinder was one joined-object. Let me say again that my method is to 'Project' a line onto a surface. Then, I move the endpoints of that line to the intersections of the surface. This eliminates a thousand errors that prevent the edge of one surface from matching the edge of the next surface. Only then do I use this line to 'Trim' the surface. Also, as I said, 'Blend' will frequently mismatch the edges of fillets, where more than one 'Blend' is required. Using 'Blend' to make cross-sections, and then using 'Network' to build the fillet eliminates those errors. When I started with MOI, I was doing what I thought should work, but when I zoomed in, I found too many mismatched endpoints. How could I avoid these? I found that the best way was always to begin with a line, adjust the endpoints, then 'Trim'. This is how I produce more than 1400 surfaces without errors.