We also have bonsai and not only make bonsai pots.
So...this is one of my big beech. I have bent it a little two days ago and cut back the branches.
It has been in its pot for about 2 years.
As it is heavy the root-cutting underneath the trunk is not easy.
By using a rope I fix the tree at the top so that I can lift it up with one hand and cut the roots far better now.
Not the final pot but a little step further.