Bamboo is such that the more powerful fibers are along the outside of the bamboo wall, just under the outside enamel coating.  The closer to the inside of the bamboo stalk the more "Pith" is found.  Pith is a kind of spongy material that doesn't lend strength to the bamboo.  The power fibers actually get shorter and fatter the deeper you go into the wall of the stalk (or culm).  Depending on the individual culm of bamboo the change form "power fiber" to pith can be very noticeable or very gradual.  Most bamboo rod sections are six equilateral triangle strips glued into a hex shape.   The individual strips are usually glued with the outer side of the bamboo -- the strong side -- out. 

    Most of the "Golden Age" bamboo rods were 9 ft long and made in three sections.  Most modern bamboo rods are between 6 1/2 and 7 1/2 ft long and may be only two sections.  To reduce a 9 ft 3p rod to a 71/2 ft 3p rod requires removal of 6 inches  from each section.  You only have to think about this for a second to see that the smooth taper that exists would suddenly have two rather large "Jumps" in it. (Remember, we're talking in thousandths of an inch.)  To build a taper that won't make the fly rod cast like a club, the taper of the sections will have to be changed.   Bamboo rods are stronger on the outside and weaker toward the center, so the ideal way to change the thickness of each section would be to remove material from the inside. This is impossible because the rod is already glued up.   The only choice left to me is to remove material from the outside. 

    Most rod builders will go to great lengths to insure the best power fibers (those along the outside of the wall.) are preserved.  Almost any tip section will be made up of bamboo that had a wall so thick that after planing to size, the entire section is made of power fibers.  It is possible to remove the outer layer of power fibers without OVERLY weakening the section.  (Any removing of material for the outside of the rod will weaken it more than removal from the inside).  What this means is that of two rod sections that are identical in dimension, one that has been made from the inside will be more powerful than one that was originally larger but had material removed from the outside.  The trick is to judge how much excess to leave for each section, to make up for the best fibers that I'm removing.  Normally 10 to 30% over the size of the taper I'm copying will do the trick. 

   What's really amazing is that, on a three piece rod, the tip section is the least critical as far as changing the taper.  That's because to change the taper of a .060 flat to flat tip 10% you're only removing .006 of bamboo or .003 inches from each side.   Very good power fibers will usually extend at least .025 into the strip.  On the other hand, a butt section might be .300 of an inch thick.  Ten percent of that is .030 or .015 on each side.  Fifteen thousandths is over half of .025.   The thicker the rod, the less you want to remove to get to your goal.

I spend most of the time trying to judge how to reduce the rods dimensions. I create a worksheet that looks something like the work sheet below.

Sides A, B, and C, are "before" dimensions of the rod section.  They are combined to make the AVG column.  DIFF is the difference between TARGET and AVG.  This tells me how much I've got to "play around with."   Notice the first three stations are the same as my target.  I can leave them along. 

The last two columns are two ways to figure the extra bamboo you'll be leaving as an additional safety factor.  The first.  ADD 10% is created by taking 10% of the difference and adding it to the target rod section.   The last column is arrived at by adding .001 to each station. (.001 to the first, .002 to the next .003 to the next and so on.) 

If  you compare the two columns, you'll see that the numbers in the first column are smaller than the numbers in the second column.   This can be true of  most re-builds, but remember that the DIFF column is made up of two tapers that may not have the same "hinges" and strong points in them.   Some dimensions at one station may actually cancel out each other.  This has to be taken into consideration.  Eventually it gets down to trial and error.  Tape on the guides and see how it casts. 

Next, I transfer the information on the taper to my work surface.    I start by putting small strips of 2" masking tape along one edge, every 5".    I write the dimensions of each station on the tape.  I draw a few reference lines on the surface so I know I'm not wandering off the area I'm trying to adjust. 

Next I have to figure the starting point of the section.  Unless you're using 6" stations, Rod sections seldom end at an exact station.  For example a 7 ft. rod is 84 inches long.  A two section rod will require an additional 1 to 1 ½" overlap for the ferrule.  The tip section will be about 42½" and the butt will be 41½", depending on the size and type of ferrule.   I use five inch stations, so the first butt measurement is at 45 inches.  That means 4 and one half inches extend beyond the station.  I place a piece of tape at this point.  It will be base for all my measurements. 

A pencil, dial caliper, old paintbrush and dustpan are my constant companions while I'm sanding the section.  I start by drawing a mark on each of the sides I'm going to sand.  This keeps me from accidentally sanding one side twice and missing another side completely.   I've learned that the best way to sand the section is to sand one side then turn the section  two flats, sand and turn two more flats.   Then I turn one flat and repeat.  When I've sanded the pencil mark from each flat, it's time to use the dial caliper to measure my progress.   I use the brush to sweep the sanding residue into the dustpan.  Keeping the surface clean and flat is important.   I also wipe residue off the rod section before I measure.   I keep the sandpaper clean with an old tooth brush and an art gum eraser. When measured flat to flat, very few rods are exact.  I mark sides that are over size and work on them.  Once again, I don't sand any side that doesn't have a pencil mark on it. How much material do I remove at a time?  Not much.   It's a feel that I've built up over the years.   I count my strokes to keep things even.   My fine sanding blocks are all longer then my course sanding blocks, but they still take off considerably less material than the course ones.   On Butts I start out with no more then 50 strokes, moving the center of the stroke back and fourth along the section.   On a tip I might start with only 20 ~25 strokes.  I always try to end up over size.  Remember, we're removing strength and I'd rather have too much than not enough!!  Additionally, I use step-down ferrules to lessen the amount of bamboo removed from the front end of each section.  Step-down ferrules gain about .015 at each station.  I usually end up flattening the taper a few inches before and after the ferrule to lesson the stress (give more flex) at both ends of the Ferrule.  Ferrules don't flex, so let the bamboo do it.

The top drawing shows how I've learned to sand my sections.  Sides A. C. and E. first, then sides B, D and F. Here's what can happen if you sand three sides, one after another.

Always leave as much power fiber under the ferrule as you can.  (ask me how I know this.)

Wrong!  This works fairly well with graphite, but this is one place where bamboo is fussy.  Look at the rod on the left.  The difference between guides 1. 2 and 3 may be fine for some formula, but the bow at A2 is much grater than B2.  That's putting a lot of stress on the tip between guides 1 and 2! 

The rod on the right has the same amount of space between the line and the rod at A B and C.  The force on this rod is more evenly balanced, both for fighting a fish and casting. 

 I've found that the distance between the second and third guide is often different than the formula I used would have it.  I've also found that the spacing across a ferrule is usually too short

And please, don't go doing this to any old Leonards or other good rods.  And don't try to pass this stuff off as original tapers, like I know one guy is doing on E-bay.