Fishing rod blanks, how they are made
The way rod blanks are made can be illustrated easily. However, to make foshingr od blanks from composite material is perhaps one the last secrets you can't find on the internet.
I have been asked a couple of time to disclose this informaion, but this something I don't find nor I don't know exactly.
The "secret" is the mandrel, the tapered shape of the fishing rod, AND the composite material.
Probably you can try designing the mandrel on a CAD software, then take it to an engineering company for the actual manufacturing. This is, I guess, done with a CNC machine. With a similar machine you can also make your own fishing reel, by the way.
Then, provided the design makes sense, you can USE the mandrel on a proper machine (something not easy to find). But you need to have an experience on how to use that machine, too!
Moreover, what composite material will you use, where do you get it from? You can do a carbon composite material yourself. This is done by chemical industries, the production volume is very high and so the order cannot be but very expensive.
Once, you managed to go through all your steps, who is going to buy your new rod? Who knows you? How can you build consumer trust?
Again, you need to inject money into a reasonable web presence and marketing strategy (both on and off-line).
In conclusion, building your own blanks and fishing rod is a very time and resource consuming business.
I would rather buy ready made blanks by respected role players in the fishing tackle arena.