Thank you Jan!
Hmm... I was also looking for bending tools but then (during the construction of my first o/b) I tried bending an empty (without teflon and flex) tube very very slowly by hand and it worked nicely.
I very light flattening is inevitable without a bending tool, but it does not affect the rotation of the flex shaft because I don't use a teflon inner which decreases materially the inner diameter of the tube.
I fill the tube with a thick white grease (for ball bearings) using a syringe before every use and this seems to work nicely.

Hmm... I was also looking for bending tools but then (during the construction of my first o/b) I tried bending an empty (without teflon and flex) tube very very slowly by hand and it worked nicely.
I very light flattening is inevitable without a bending tool, but it does not affect the rotation of the flex shaft because I don't use a teflon inner which decreases materially the inner diameter of the tube.
I fill the tube with a thick white grease (for ball bearings) using a syringe before every use and this seems to work nicely.