Fiberglass: First we have to make fiberglass. This is done by melting glass & lowering a drum or spinning wheel into the molten glass. The wheel or drum is then removed from the melt, drawing out fine fibers. These fibers are then spun into a yarn or rope or are woven into a sheet. Traditionally (but not always) it is these sheets that are used to make fishing rods. Now let's make a rod.
Fiberglass sheets, or cloth, are impregnated with polyester resins & wound tightly around a removable steel mandrel. Shrink tape is then wrapped over this very tightly & the whole affair is placed in an oven to cook for a while. During the cooking process, the shrink tape squeezes out the excess resins. After the cooking & the blanks have cooled the shrink tape is then removed. Finally, the blanks are lightly sanded to remove the small ridges left by the tape.
Graphite: The process for making graphite blanks is almost exactly the same as for fiberglass except the cooking temperatures are much higher. Also, instead of sheets, often a graphite tape is wound around the mandrel. This tape has a fiberglass backing, or scrim. The graphite fibers traditionally run the length of the tape, while the fiberglass fibers of the scrim run parallel. All in all the processes are quite similar.
So how do they come up with different rod weights & actions? The key is the amount of material used at certain locations along the blanks length. While the taper of the mandrel is very important, the real art is in how you cut the fiberglass or graphite that you wrap around it. The shape of the cloth or tape is essentially a right triangle with the sharp point cut off ("L" shaped). The third leg of this triangle may be altered & have many angles in it. This will determine the final taper & action of the rod. Manufacturers spend much time & effort determining these shapes. It is the heart of the rod. I should also mention that some of these shapes, or patterns, cut into the material are closely kept secrets.
How do they make all these rods different colors? Well the rod is colored in two ways. One way is to put pigments into the resins on the tape or sheets, so the raw materials are the color (or close to the color) of the finished rod. Another method is to dip-finish the rod in a colored coating after the sanding.
So there you have it in a nut-shell. Of course there are other machines used like hot irons for heating & rolling tables to wrap the mandrels tightly, etc. I should also mention that any one of these processes can be modified in an infinite amount of ways. Every manufacturer has their own methods (& secrets), but this is the general way of making rod blanks. Something to think about the next time you string up your graphite or fiberglass fly rod.