HOW TO CALCULATE A FOUR (QUAD), FIVE (PENTA) OR EIGHT (OCTA) ROD TAPER AND SWELLING DUE TO SOAKING

The simplest idea to transform the taper from a famous six (hex) strip rod is to keep the mass (weigth) distribution equal. This is achieved simply by calculating the cross area of the rod (consisting of 4, 5, 8 or 6 triangels) at each point (form stations) to be same as in the six strip rod. This results in quite simple formula which is included to the EXCEL file (TAPERCALC.xls) included.

The formula used for QUAD (4) strip taper is based on ratio 0,93. Theoretically (moment of inertias) it should result in 4% stiffer rod compared to a HEX with same mass. Some builders like to have the ratio 0,95 which naturally gives a little stiffer rod.
To modify the ratio you may change the parameter value from 0,93 in the formula to 0,95 in column A6 (red).

The soaking of the strips for 3-7 days is water (with some bleech to avoid the smell) is a simple way to make the planing very, very easy. Typically the strips are heat-treated before the final planing.

I have made some experiments and measured the swelling of the cane strips and resulted to use a swelling factor of 3-5% (1.03-1.05) for 4-6 days soaking. This is, of course, an approximate but it is possible to make rods by planing soaked strips with 3-5% extra diameter, then heat-treat and glue together. It is almost too easy, dont tell it to anyone! The final diameter is certainly not 100% accurate but it is accurate enough for a hobbyist like me not selling rods to anyone.

HOW TO USE TAPERCALC EXCEL PROGRAM?

Just give the rod diameter values to the column B.
Give the swelling factor value (e.g. 1,05) if desired.

All the input values are in RED COLOR

NOTE: There are two spreadsheets included: one for European rodmakers converting the funny inch -values to millimeters and a second sheet with the traditional values in thousands of inches.
The values in the sheet are from the famous Driggs River Special rod by PH YOUNG

Please, be free to make experiments and enjoy!

Go to TAPERCALC.xls EXCEL program