[sinker]

I'm not sure what went wrong exactly, but a common issue people run into with lofts is caused by the fact that FreeCAD tries to match vertices to vertices. If you use the split edge tool on your square to create 8 edges out of the existing 4 (maintaining the same square shape), it should loft smoothly to the octagon.

If the loft appears twisted it only means you need to change the order in which you created the geometry. FC in addition to matching vertex to vertex will also match them in the order they were created. This allows you to purposely create twisted shapes, but sometimes can happen inadvertently also.

[bambax]

Here's a photo of the church tower in question:

https://img.over-blog-kiwi.com/1/40/25/08/20170227/ob_76f390...

You can see that the square base is connected to the octagonal tower using alternating trapezoids and triangles; FreeCAD doesn't seem capable of doing that using the GUI (but I'm no expert and would love to be proved wrong).

[alright2565]

This is what the other person was trying to describe: https://imgur.com/a/J9lQBNK

I chose 1mm for my corner chamfer on the base, but you could make it any dimension including something imperceptible.

[bambax]

Aah thank you!!!

Yes that would have worked, I will try that next time. The last image is more or less what the Python code produced, but being able to do it in the GUI would be nice.