ROD BUILDING TIPS
CC Consistency
By Tom Kirkman


This question is from Volume 6, Issue #4 of RodMaker Magazine:

I've been using the Common Cents method on all the fly rod blanks that pass through my shop now. But I'm having a problem getting the same readings twice. I had a GUSA blank that I tested and recorded the stats on. A week later I was showing a customer how I rated thses blanks and used the same GUSA blank for the purpose of illustrating everything to him. I happened to look at the ERN rating I got that day and compared it to the ERN rating I got the week before and they were quite a bit different! How can this be? I compared a few other rods and found the same thing. My ERN ratings are changing from week to week. Any help is really appreciated. Mike, Greenville, SC

If you're using the exact same blank, then we have to assume the inconsistency you're seeing is due to some sort of inconsistency in how you're implementing the system. There are two main areas that simply must be carefully controlled, if you going to get consistent results.

The first regards the use of the Cents you're using to take your measurements with. The Common Cents System dictates that you must use pennies minted during or after 1996. Pennies minted prior to 1996 have a different weight than those minted during and after the 1996 year. So if you just use a random handful of pennies for taking your measurements, you're not really using the same constant to get the required deflection.

How much difference could having a few pennies minted prior to 1996 have on your results? Quite a bit, actually. Let's say your first rating required 40 pennies to get the required deflection. And in those 40 pennies you had 15 that were minted prior to 1996. Now let's say you repeated the measurement and this time you had 20 pennies minted prior to 1996 in the amount needed to attain the required deflection. Because of their greater individual weight, this time you might only need 36 pennies to get your deflection. Suddenly the same blank has changed its ERN by nearly a full point! The Common Cents System is sensitive enough, has enough resolution, that not using the prescribed weight constant will have a measurable effect on your results. Use only clean pennies minted after 1995.

The other variable regards the orientation of your blank during the deflection phase. Most rod blanks varying in stiffness or power depending on the axis you're working against. Remember that the wall thickness on most blanks is not consistent. This is one of the manufacturing anomalies that contributes to what we callthe spine effect and it plays a role in the power or stiffness that a blank has on any given axis. While the difference is usually slight, the Common Cents System is sensitive enough to easily discern differences in power on any axis of the blank.

Thus, if you take your first reading with the spine up, then all future readings need to be taken with the spine up as well. If you take your reading with the blank's natural curve in a particular position, then all future readings must be taken with that curve in the same position. This is the only way to get consistent results. In the Volume 6 #3 issue of RodMaker, we covered how to "zero" the tip and the importance of using the same blank orientation for each measurement. For future measurements, I'd suggest you mark the blank butt in such a manner so that any future readings can be made with the blank in the same orientation.

When you become consistent in how you implement the Common Cents System, you'll be able to get far more consistent results. ~ Tom Kirkman

Publishers note:

If you have any tips or techniques, send them along! Help out your fellow rodmakers! ~ Publisher, FAOL

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