When it comes time to build a fishing rod people often ask what is a back bone and how do you locate it? Both these questions are very simple to answer. To begin with you need to understand how a blank is made and the processes it goes through before it’s available as a blank. Most understand that blanks are made using several different layers of cloth to make up its mass and that these sheets are rolled around a mandrel to form its taper. Its all in how these sheets of cloth are laid that gives us one back bone or multiples. To begin with you need a mandrel, that’s a long piece of metal that the cloth will be wrapped around to form its shape and taper. The diameter of the mandrel, tip and butt will determine the rods action. Mandrel’s can be made from alloy, mild steel, high speed steel it doesn’t matter, as long as the mandrel is clean and straight as a die.
To begin with we take a mandrel and apply a release agent over its entire length. This will enable us to remove the mandrel from the inside of the blank upon completion. Once the release agent is applied we take a roll of cloth from the freezer, cloth needs to be stored in a freezer because its pre impregnated with resin. We then use either meserments or templates to cut out the cloths shape which will also determine the rods action and power. If we were going to make 20 blanks then we would cut enough cloth to do the whole run in one go. We now have our cloth cut and ready to be wrapped on the mandrel. We take our hot TAC iron and we carefully press this onto and against our cloth and mandrel. This makes the cloth edge stick to the mandrel so we can roll it with out the cloth moving every were. It’s absolutely critical that the cloth be laid with the fibre running up the blank in a 0 degree orientation. If the fibre runs a bit of centre then it can and will weaken the rod by more than 40%.
Now, this is where things become a bit more complicated. We take or cloth and mandrel over to the rolling table. This table has one huge hydraulic arm that moves up and down and from front to back. The table in which the mandrel and cloth lay on is called a plenum. This plenum can be an air bag style; it can be just a hard bed with some fine cloth on its surface. The idea of the plenum is to keep the mandrel hard on the flat surface while it is rolled back and forth by this large hydraulic arm that compacts the cloth into a tight roll around the mandrel, sort of like rolling your own cigarette. Now this is where we start forming our back bone in the blank. After rolling the first sheet of cloth, we now have a start and a finish point that don’t match up. What this means is that the beginning of the cloth were we tacked it onto the mandrel using the TAC on iron is overlapped by the end of the same piece of cloth. The tail end of the cloth may only overlap by a ¼ inch but it now means that there is more material in one section than the other. This over lap means an extra thickness in the overlap of around 0.15 which isn’t much at all. When we lay another sheet of cloth on the same thing happens. With every layer of cloth that goes on you will end up with some degree of overlap, it can’t be helped because the diameter is always changing.
Once we have laid up our last flag we then take the rolled mandrel to the cellophane wrapping machine. This contraption is going to roll cello tape around the blank from tip to butt maybe twice under a pre determined load. The purpose of cello tape is to compact the fibre and force out any air bubbles and excess resin. Cello tape is also heat resistant and contracts in on its self some what like heat shrink. Why? Because we are about to hang this blank and mandrel up in an oven for around 3 hours at 120 C. The heat softens the resin in the cloth making it run and fill any voids. With the constricting nature of cello tape the resin and any air bubbles are soon displaced to make a solid walled blank. While the blank is being baked, you get a bit of movement in the wall of the blank, material is moving along with resin flowing and air escaping. This is were we start getting irregularities with in the blank wall. Again this all adds to what we call the spin and in some cases multiples. After three hours the blank is taken from the baking oven and then placed in a tank of water to cool the blank, mandrel and to aid in the removal of the cello tape. The blank is then placed in a hydraulic pulling ram to remove the mandrel. After the removal of the mandrel the blank is trimmed to suite, the tip and butt is cut to the pre determined length. Back bones or spins as some call it is in fact a defect of the manufacturing process, a perfect blank is one with out any distinct backbone. And this is exactly how a backbone is formed; hope all of you have learnt something.
Stuart Mackenzie
Precision Rods
Reply With Quote
