Hi Gilberto,
You may not be aware of my detailed work on slashed beams and slashed stems that I recently contributed to openlilylib. Theres a function that provides fine control over the parameters of beam slashes, and which works on the left as well as the right (needed for many contemporary scores). Also, another library function for individual stem slashes, motivated by a need to have horizontal slashes, but I generalised it to do any angle, again with fine control over many of the parameters such as thickness and fractional position.
You can find the code under the /slash-beam and /slash-stem directories under /notation-snippets in the openlilylib/snippets repository, complete with examples.
I think you have somewhat different use case to me - I needed individual control finely tuned, but is it that you want the function to automatically compute a variable angle but based on some beam criteria? I am sure something like that could be added to my code. The code I have submitted has been pretty heavily tested, and apart from anything else, has some lovely trigonometry!
Hope this may be helpful.
Andrew