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With so many smart people on the list I am sure some one knows the formula to find the width of a penta strip that is 72 degrees. I know that a 60 is 1.155 and a Quad is 2 but what is it for a Penta? I bevel on a 60 and would like to be able to figure the width for a measurement. (David Ray)
From trig:
If the height (h) = 1, and the width is 2w
then tan(36) = w/1, so w = .7265 and 2w = 1.453
So the width factor for penta's is 1.453. (Tim Preusch)
I'd love to have the formula. Last winter, I couldn't find the width of a flat (1.155) reference and was forced to break out old math books. I dusted off my old TI55 calculator and tried a bunch of SIN/COSIN/TAN calculations and couldn't get it figured out. Found the reference to the 1.155. Thank goodness. Mind you I had a lot of fun working on this (diagrams, calculations, etc.).
So what's the equation to get the width of a flat if you have the angles and the height of a triangle known? (Scott Turner)
The general formula for all isosceles triangles is:
Width Factor = 2 times the tangent of half the apex angle
or W = 2 tan(apex/2)
Hex: W = 2 x tan(60/2) = 2 x tan(30) = 1.155
Quad: W = 2 x tan(90/2) = 2 x tan(45) = 2
Penta: W = 2 x tan(72/2) = 2 x tan(36) = 1.453 (Tim Preusch)
It should have been obvious, but it took a parabolic penta to really make it evident to me. A penta is a lot stiffer on the forward stroke than on the back stroke. Needing some numbers to compare, I suspended a weight from the tip and measured the deflection with the rod oriented horizontal normally (guides down) and then upside down (guides up). The deflection is 21.5 inches normal, and 19 inches upside down. Same weight, same position, same yardstick. The pentas I made before were all faster rods, and the difference wasn't as great, I never noticed it before.
So, is this an advantage? I think so, being able to shoot line more on the forward cast, with the softer backstroke protecting a fine tippet better. Might take some getting used to the casting though. (Darryl Hayashida)
The different stiffness in different orientations is called spine. The stiffness is most easily documented with Common Cent system. In 2003 after some penta rods I made an extreme penta rod using five quad strips with extreme asymmetry and very strong spine.
It is really powerful in forward stroke but not very stabile, easily twisting to lateral directions. When turned 90 degrees in my hand it is much slower but you can throw as much line in that direction, too. Very instructive rod! (Tapani Salmi)
I was wondering if anyone has any suggestions, tips, or tricks on chucking up a Penta blank to turn it for ferrules. A six sided rod works just fine with three jaws, and of course a four sided works with the four jaw chuck, but the Penta well the Penta. Any suggestions other than rolling it on the pants leg with a piece of sand paper held on the end. (Floyd Burkett)
I've never done it, but couldn't you make a wooden sleeve a little like a collet for those penta sections? I suspect the sleeve could be round both internally and externally and still manage to apply enough pressure to keep the penta section sturdily held. (Harry Boyd)
Get a piece of tubing a bit bigger than the penta OD. Build up the penta with tape until it jam fits in the tubing. That's accurate enough, but if you want a bit more make a wooden split chuck. Drill out a dowel just slightly oversize. Saw cut a slit in the dowel from center to edge. When put in a chuck, the slit will close, pinching the section. (Tom Smithwick)
I use brass tubing of various sizes. Simply cut a slit it them and chuck them up over the appropriate section of your penta rod. I would imagine other materials would also work fine. (Larry Tusoni)
