How do I make a flexible pointed tip quill for line variation?

As I’ve been researching, I learned that quills actually have two historical types of cuts: the older rigid broad-edge and flexible pointed tip (developed later for Round Hand and faster writing styles).

Quote from text:

"However, to write a faster (or “running”) version of the Bastard hand and to draw the “cadels” or flourishes, the French masters used what they called the “plume à traits”, which was as sharp and narrow as possible, and flexible."

source 1: https://pennavolans.com/pointed-or-broad-which-is-the-best-nib-to-write-copperplate/

From Shelley, Second Part…., 1714. n°2 and 3 for square and German Text, n°4 for Round Text. Lenghten the slit for italian hand and for flourishing. N°5 for Running and mixt secretary, n°6 for Set Secretary and Engrossing hand, n°7 for Court Hand,

source 2: https://fprevolutionusa.com/blogs/news/dip-pen-nibs-evolution

https://preview.redd.it/n04dt1tcr2ph1.png?width=2191&format=png&auto=webp&s=4286fd83fbc6f0a6a9fef392330b119124d101e7

Virtually all the tutorials and instructions I can find online only show how to make a old broad-edge rigid quill.

Does anyone here know how to cut a true pointed-tip quill that can produce nice "hairlines" under zero pressure, but splay open to create a wider line when pressure is applied?

I've been trying to make one myself but haven't had much luck yet. Any advice or historical resources would be great.