It all starts with a 12 foot culm of bamboo

Bamboo Rod Build, Part X, Hollowing

Hollow building bamboo fly rods is a concept that has been around since EC Powell's patent in 1933. Later, Lew Stoner of Winston took the idea one step further when he developed his hollow-fluting method.

So why do some go to the trouble of hollow-build their bamboo rods? In my experience, hollow-building a bamboo rod creates a rod that is 20-30% lighter than a similar solid-built rod. Hollowing a rod also provides better balance, and, most importantly, it makes a rod that is smoother and crisper to cast. Although the stationary math may tell you differently, in my experience, hollow building a cane rod actually makes the rod's action faster, and much more responsive.

Although the advantages of hollow-building are most evident in rods 5 weight and heavier, I recently hollow-built a 7 ft, 3 wt rod, based on a taper that Tom Morgan graciously shared, The rod's total weight is just 3 oz. and it's one of the finest casting 3 weight rods I ever has the pleasure to use:


The first element at work here is the elimination of "swing weight" that has to recover during the bending action of a rod. Since most the resilency of bamboo is supplied by power fibers plentiful at the surface, scalloping off the apex, espeicially in the butt section of a rod, eliminates much of "pith" weight that contains significantly less power fibers and, as such, is just "along for the ride".

The apexes are scalloped, rather than flat planed off, because scalloping retains wider "glueing edges", which help ensure the rod's integrity: Here's a picture of how the butt end of our hollowed rod will appear:


There's also another factor at play here, a factor I knew existed but never saw acknowledged publically until I found a blurb on well-known maker Bill Harms' web site. The vaults created by hollowing add an additonal element of resistance or stiffness to a rod because the same bending force is applied to a smaller surface area. It's the same physics at play that makes us all a little nervous when a woman walks across our hardwood floor in spiked heels.

Although some makers recommend increasing the taper of a rod when hollow-building by 2 to 4%, I've had excellent result by using the original taper. I just seem to end up with a smoother, more responsive, better casting rod, IMO.

The MHM using radial cutters to flute or scallop the pith side apex off the strips:


A spring-loaded roller is added to keep the strips in place on the anil as the strip is hollowed:


A zero taper is set all along the top of the anvil. Most makers like their rod sections to be solid for 2" at the ferrule stations. Since the strips are already tapered, the fluting cutter automatically digs into the the apex at a consistent depth that lessens as the tip end of the strip is approached. Shims, in this case 0.030" orange plastic strips, are installed under the flexible HDPE anvil to raise up the strips only in the areas we want to hollow. Notice how there are no orange shims near Station 13, which will be the ferrule station of our butt strips:


Typically, tips strips are taken down to a wall thickness of 0.060", while butt strips are fluted to a wall thickness of 0.070". The wall thickness is measured with a micormeter fitted with a 0.500" tip. The measure shown of 0.572" here shows I have achieved my desire wall thickness for my butt strip plus approximately 0.002" for enamel than will be sanded off later:


Once the first desired hollowing is achieved on the first strip, the hardstop is set so that the remaining 5 strips will be hollowed to the exact same depth:


Finally, after the strips are hollowed to the desired depth, the interior of the flute is cleaned with a wire rush:


Six butt strips, ready for glue-up:


The same process is followed for the 12 tip strips. Since the tip strips are much smaller in height than the butt strips, the hollowing actually stops about a third of the way from the tip station.