What species do fish for with your bamboo rods?




View Results
Free poll from Free Website Polls
 

Ask About Fly Fishing

affiliate_link
 

Pentas

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 TI-55 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)


Has ANYONE EVER come across the results predicted by Garrison regarding the top glue line of a well used penta rod.  Was reading his theory found in the back of the book - page 286 in my copy where he states:

".... But when the end is reversed, the fibers of the point are under end-wise squeeze- compression.  There is insufficient binder to keep them in line.  They have to go somewhere under that relentless push.  So they buckle sideways in one ore more likely both directions.  The caster becomes aware of this when the fibers in the point of his Five crack off the rod."

Has ANYONE EVER HAD THE FIBRES on the top joint or glue line of a penta crack off the rod??  Or have on presented for a repair - EVER? Sounds like hyperbole to me as I have a hard time following how they would wear out faster let alone crack off - ANYONE??

"Endwise squeeze-compression"??  Seems like by design and if built correctly such a rod would track or maintain its casting plane better if anything.  Comments appreciated.   (Rob Smith)

    He is describing the terminal stress failure mode, you will not be able to create this in any normal fishing situation!  (Robin Haywood)

      That’s basically what I'm thinking as the taper if correctly designed will never reach or allow such stress points - does this make sense?  (Rob Smith)

        It would in fact be very hard to find a rod whose tapers actually did create such stress concentrations, ferrules are probably the worst places for shear stresses, but the little splints help to reduce it to acceptable proportions.  (Robin Haywood)

    Since I have built several pentas I would be interested in any responses to the question of tip problems with the penta, or any known problems with pentas for that matter. So if you respond off list to the question would you CC to me also. TIA  (Floyd Burkett)

      I have been just curious about the geometry of Penta. As stated in "Master's Guide", Penta is not plane symmetric for up and down when it is made as a rod.

      In this case, the point of apex (upper side of the rod) and the point on the flat (lower side) has different distance from the center line of the penta.  Apex distance is the one for radius of outer circle and the flat distance is the one for apothem.

      Garrison's hyperbole comes from this fact and the calculation of the stress on both of the points become different.  This is assuming the center line of penta resides always at center.

      Do you think that the center line is always kept as "center" when the penta rod is flexed up and down?

      I wonder if the apex side has more resistance than flat side, then the center of the rod might shift when flexed.

      Appreciate physicists' opinion.  (Max Satoh)


 

Site Design by:  Talsma Web Creations

[Tips Home] [What's New] [Tips] [Articles] [Tutorials] [Contraptions] [Contributors] [Contact Us] [Taper Archives] [Christmas Missives] [Chat Room] [Photo Galleries] [Line Conversions] [The Journey] [Extreme Rodmaking] [Rodmaker's Pictures] [Donate] [Store]