Hobbies And Interests
Scarf Joint
A scarf joint is used to splice long lengths of wood or bamboo together. Imagine, for example, two boards, one inch by one inch and ten feet long. To joint them with a scarf joint, a bevel is cut in each board -- perhaps five feet long. The two beveled edges are then glued together to make a single board, 15 feet long, with the full length of the scarf-cuts overlapping one another. There is such a large area of glued surface, it's a very strong joint and remains flexible like the natural fibers.
Ferrule
A ferrule is a metal joint -- with two sides -- a hole and a prong that fits in the hole, forming a press-fit mechanical connection. Modern fly-rods are easy to make in any contiguous length you want, but classic split-bamboo fly-rods are limited by the length of bamboo that can be found free of nodes, which are the notches found intermittently in bamboo. So, bamboo fly-rods tend to have more ferrule connections -- not just for the sake of breaking the rod down for packing or convenience, but as a limitation of clear bamboo fiber lengths.
Benefits of Ferrules
Old bamboo rods frequently came in sections greater than two: a butt section, one or middle sections and tip sections. Unlike modern fly-rods, bamboo fly-rods tended to come with more than one tip section -- perhaps even three -- in anticipation of breaking them because the tips are so fragile. Ferrules give you a rod with interchangeable sections. Break a tip section in a three-part rod with no scarfs in any of the joints and simply replace it with a new section. Break a tip piece in a two-part scarfed-tip and you'll pay more or do more work to replace it because scarfs take much more effort and skill than ferrules.
Benefits of Scarfs
Ideally, a fly-rod will have a compound bend. So, from tip to butt, the rod gets more rigid, inch by inch. This gives the rod a desirable action; it's easier to cast and easier to hook and play fish. Ferrules do not bend. So, every place there is a ferrule, there is a completely rigid section of the rod -- a flat spot in an otherwise compound bend. So, if you make a five-piece rod, you'll have three ferrule joints interrupting the flexing nature or "action" of the rod. If, by using scarf joints, you can use just one ferrule, you'll have a much more enjoyable fly-rod.