The placement of guides on the rod is essential in distributing the load along the rod's length to allow the rod to perform at it's peak potential. The guides transfer the load of a cast or the load of a fish-on, from the thin sections of the rod to the thicker areas near the butt. Placement of the guides vary according to line weight, length of the rod, action of the rod, and the casting techniques of the individual. A couple generalities exist: 1. The total number of guides is generally one more than the total length of the rod. 2. The guides are identified starting with the first guide just below the tiptop. 3. The guides get larger as you get an increase in rod length and line weight. Opinions vary as to guide positions and the size of guides. Exact locations may also have to adjusted depending upon the multiple sections of the rod and it's ferrules. Art Scheck wrote a very good book on rod building, "Fly Rod Building Made Easy", 2002. He takes a mathematical approach to guide spacing from the aspect that the load creates a curve to the rod that necessitates a particular positioning of the guides. Assuming that the stripping guide is always positioned 30" from the bottom of the reel seat and the the first guide is 4" from the tiptop, he solves the placement of the guides with the distance between the stripping guide and the first guide with the formula: 4 + (4 + x) + (4 + 2x) + (4 + 3x) + (4 + 4x) + (4 + 5x) + (4 + 6x)... This formula allows the guides to be positioned at a progressive rate based upon x. For example: an eight-foot rod with nine guides would be 66 = 36 + 36x (66 is the distance between the stripping guide and the tiptop). Solving for x would be 0.83 . By substituting .83 into each of the expressions, one can get the distance of each guide from the tiptop.
Skip Morris wrote an excellent book in 1989, "Custom Graphite Fly Rod". Skip tends to place an extra guide along his blanks in order to keep the guide sizes smaller. Smaller guide sizes results in less overall weight. His spacing tends to be more uniform than as progressive as Art's. Remember that the curve of a rod differs under a load from one manufacturer to another. Fast actions rods tend to have more curve in the upper part of the rod and this will affect guide placement too.
Bob Widgren is a custom rod designer out of New Mexico,Los Pinos Custom Rods. He has put together literally thousands of rods. He tends to place his guides with a progressive rate similar to Art. Note that Bob and Art both tend to prefer larger Stripping guides than Skip. This has been a trend in custom rods from the aspect that the larger guides will cause less friction on the casting release resulting in longer casts. Many manufactured rods will retain the smaller stripping guides due to the asthetics of appearance. Bob has a more detailed Guide Chart on FlyFisherman's Web site. Check out: Bob Widgren's Guide Spacing Chart