So onto the next stage of the build, probably the most interesting part, the actual design. Being as the thread has been bumped up tonight I'll post this.
As per the previous post the rod was required to have the following characteristics:
Be able to cast long distance 100yds plus, BUT be able to pick up line at distance quickly to enable instant striking.
Be able to be used in hit and hold situations.
Be able to subdue large fish but retain a sensitive, responsive feel.
I also added another criteria in that the tip should be fine enough to show twitches and small pulls.
So as per the last post a very large parcel came with Chapman’s labels on it which was the bamboo to be used for these (and other) rods.
I had spoken to John Chapman at length and he selected the bamboo to suit the build design. Now what is interesting here is that at every stop in a bamboo culms life it adds to its price. So the costs from the grower, the costs for the buyer/selector, shipping to a distributer who then puts his profit on plus another lot of shipping costs and finally to the retailer who again has his profit margin and additional carriage costs if you can’t physically pick it up yourself. Now in the past I, like many others, have attempted to intervene and buy it as far up the chain as possible to keep down costs, usuaually by buying direct from some overseas distributer.
This time however I bought direct from John Chapman and the main difference from the off was that I was speaking to an outstanding rod builder who completely understood what I was trying to do. We discussed node spacing, decorative finish and tapers. John then sorted for me culms cut exactly to what was required and even marked each culm as tip1, butt1, tip2, butt2 ( B1,T1,B2,T2 etc). If I would have bought culms from a distributer I would have had to buy them at least 8 foot long to allow for node spacing and also buy some extra culms to ensure there were no damaged ones etc etc. If I bought extra long ones I couldn’t be certain that all the length was suitable for purpose, so overalI would have had a lot of wastage with offcuts I couldn’t really use for anything else. John’s culms were already sorted and at 6’2” I only had to cut off 2” per culm which was not only a saving on the material costs but also postage. Just a thought to consider when embarking on a larger project.
the culms that Chapman's provided. John had maked each with butt or section info and were cut to allow node spacing with only 2" wastage
Ok now to the design aspect.
Richard Walker said of designing rods: “Rod designing is part science and part art. Knowledge of mathematics and physics can carry a designer far, but not all the way. For the rest, he must surely rely on his angling knowledge and what can be best described as a sense of proportion”
Bob Millward in his book Bamboo, Facts, Fiction and Flyrods 2 also has a diagram on rod building which depicts a circle of knowledge. It is a bit tongue in cheek as it’s full description details the downside of being too busy building rods to actually fish but it starts with:
Science + Craftsman = Rods
He then goes on to show that:
= Rods + Knowledge
Practice Hand + Eye
He then shows Rods circling back into Practice, and Knowledge circling back into Theory, so therefore the more rods you make the more practiced you get and the Knowledge you gain increases your understanding of the Theory.
So I needed to scope out the rod which was in my head into a practical example. I didn’t have a rod to study at this size so I used the experience I had gained when working in the Radio Engineering environment when trying to replicate faults or events, namely reverse engineering. I didn’t have an example either physical or mathematical (taper sizes in increments), but I did have examples of what I didn’t want. I had the dimensions of the MKIV which wasn’t suitable for this rod and I also dug out a 10’ cane sea fishing rod which was way over the top for a coarse fishing rod. So I now had the two extremes of the basic build requirement- one too soft, one much too stiff.
Two rods used to reverse engineer what I required.
I plotted the taper profile of these rods onto graph paper and compared them. My rod would sit somewhere in the middle of these two, although much nearer to the MKIV than the sea rod..
I then put in the first of what little known data I had. The very tip of the MKIV is quite responsive and on a recent winter trip to Redmire the tip had shown the presence of a fish mouthing the bait long before the indicator had. It had shown up little tremors and pulls admirably. I now knew that the MKIV tip size was acceptable so I plotted this first dimension on the graph but at the 12’ point not the 10’. I then had another look in the rod rack and selected a very stout rod, a 3 section all split cane Priory rod. This is a beast of a course rod with a very powerful butt section, which I had been impressed with when fishing the Trent for barbel with a certain Mr Brookes. I also had a chance to see its power curve when I snagged the bottom (no barbel that day for me) in quite a fast current. Although too fast a taper throughout and too slender for what I wanted, the first 4 foot or so was a good starting point for the butt section so I plotted this on the graph. I now had a rough starting point and ending point. Drawing a straight line between the two wouldn’t make for a good rod however tempting it seemed, although some cheaper mass produced rod were made like this rather than a series of complex tapers that most of us would like to believe.
The next stage I cobbled together a makeshift prototype with the Priory butt and a MKIV tip and a 31/2’ middle section quickly made up with projected dimensions and glued together. For the first time I could see roughly what the finished rod would loosely resemble (very loosely)! The middle section I had made did match the butt section taper but obviously the top of it in relation to the undersized tip section was an area to work on. I measured the rod for the exact middle at 6’ and marked it. I then measured the blank and plotted this measurement onto the graph giving me a notional middle point and dimension.
Ok now with 3 points, top, middle and bottom plotted it was time for the calculator to make an appearance.
Before I start this just let me say I’m no maths or physics whiz. Most of my time in these lessons at school were spent gazing at Karen Westwood’s chest which was developing at a phenomenal rate. Add into the mix the fat bald headed science master who was effectively useless. Being bald and fat suited his persona as a science master (sorry Snape) but the same look didn’t suit the maths teacher due to her being female although she seemed to bear it well.
Anyway…back to the plot.
Richard Walker let us know that the deflection of a rod = wl3
This is where
is the load
is the length
is the modulus of elasticity
is the moment of inertia.
The modulus of elasticity E is a function of the material, and the moment of inertia is a function of the cross-section, which he very helpfully tells us is 0.06 d4 for a hexagonal rod, where d=diameter, which lucky for us is what we are building.
It can be seen then that Deflection varies as wl3
With this formula alterations in diameter and therefore test curve can be made to an existing design or new design if key point dimensions are known.
For example, if we take an existing MKIV and attempt to decrease its test curve by 10% we reduce d
to 90%. As we are using the value d4
then that is 90% of 90% of 90% of 90% which is 65.61. If the length l
and the deflection are to remain the same, then the load w
varies as d4
changes, ie if d4
is to be reduced to 65.61% of its former value so also will w
be reduced. We used a MKIV as the example with a TC of 1 1/2 lbs; so 65.61% of 1 1/2lbs is 0.98lbs. So we have effectively reduced the tc by as near as 1lb. So we can say that by reducing the loading of a rod by 30% for the same length and deflection we need to decrease its diameter by 10%.
Why is this of interest? Well quite simply if we increase the MKIV by 10% then we increase
its test curve w
by 46% . Ah now the penny is probably beginning to drop. We have calculated the dimensions for the MKIV SU. Now I have already dismissed building a SU version of the MKIV as SU rods never feel really quite right in my mind. So bear with me for the next bit.
If we increase the length of a rod it means a decrease in the loading for the given deflection and diameter. RW tells us that a 10% increase in length means a TC decrease of 15%.
So using our MKIV as the starting point we can calculate the dimensions of a 12’ rod, adding back the decrease, then add the necessary increase in test curve to get it to say 2 ½ lb test curve and see what we have got. These dimensions are then plotted on the graph as the first guidelines as to what our new rod will follow. It’s OK saying just bung on 10% to the dimensions of any rod and you get a SU version without knowing why, but once you actually understand what is behind the figures you can adapt of lot of rods for specific purposes.
This picture is of my dog Millie. It has nothing whatsoever to do with the thread but I thought you could do with a little light relief at this stage.
We aren’t finished yet though. This is only a plotted 12’ approx 2 1/2lb TC rod which has a similar action to a shorter MKIV, which is not what we wanted. To get the action we wanted it’s now necessary to build on the basic theoretical blank.
The good news is we can now get to the stage where RW described that mathematics and science get us so far, but angling knowledge and a sense of proportion gets us to the finish.
A percentage increase was added to the butt section to make the taper more shallow to stiffen it. The cross over point in the middle of the rod was addressed next. The tip was given two compound tapers. The first was about two foot below the tip to transfer the fineness require for bite detection into a bigger dimension to enable the tip to pick up line quickly. This compound taper is quite aggressive and can be seen easily with the eye on the blank before it is whipped over with intermediates. The second compound taper is about two foot above the ferrule and not quite so aggressive. This brings in the butt section taper into the tip so that the action is smoothed out. Without this the butt would be stiff and all the give would be solely in the tip from the ferrule upwards. This smoothes out the action. All the dimensions are in a calculated + size as you can always take an extra bit off if it doesn’t suit, but you cant put it back on if it’s too small!
Ok that’s it for this instalment. A bit of a dry read but it explains the working out and theory behind the rod. Next instalment we actually get out the tools.