The FCStd-files have been made with FreeCAD 0.18.
Nothing specific.
I've printed the first test with 10% and 2D-grid infill pattern and while tightening, I could hear the first crackling noise.
So - go for a more dense infill and a 3D-infill pattern, e.g. 3D-gyroid. Choose 3 outer shells for improved stability.
And maybe you want to print it rotated by 90deg relative to the model's original orientation. By that you load the handle ‘in printing plane’ which increases the stability significantly.
The author marked this model as their own original creation. Imported from Thingiverse.