I'm attempting to make a model of the crane pedestal as in this image here.
https://img4.fleetmon.com/originals/gms-endeavour-6102_9558983_991095.jpg
I've used a lofted boss, and guide curves but I can't seem to stop the flat sided areas ballooning out.
I've considered using a sheet metal part as I know that can give me a square to round as in the picture, but as what I'm doing is for illustration rather than something we are construction it seems a bit of overkill.
Benedict,,, I couldn't view your jpg for some reason but I'm wondering if this might lead you in the right direction. This has just a top and bottom profile. The top is a 20 sided polygon and the bottom is a square. Run the loft command, select the profiles then right click and show all connectors. Then drag the appropriate connectors on the square sides to the corresponding corners. The result is all planer faces.