I may be showing my ignorance here, but is it feasible to use a solid material to create the same effect as a thread wrap to protect a female ferrule end from spitting? Possibly antler, corrian, a very dense wood, hard rubber or (if you can get it) ivory? If the inner surface was carefully worked to match the taper of the ferrule and then adhered with rod bond, could this work?

Rodney

I think that any hard material fitted tightly against the blank might be asking for trouble by creating a shear point. I would think that there would have to be a certain amount of flex as the blank will change shape slightly under load (I think)

Mike (Southgate, MI)
If I don't want to, I don't have to and nobody can make me (except my wife) cuz I'm RETIRED!!

i would agree with mike. anything that does not flex will create very large stress concentrations at the edges... i would assume the longer they are, the worse stress concentrations it would create.

My Outcast and BigCatch rod blanks from Korea/China? come with a chrome looking piece at the female end of the ferrules. Up to about 1/2" long on ultra heavy duty surf rod blanks. No reports of shearing that I'm aware of. Here in Hawaii these rods are ABUSED.

Mark, what material are those blanks made out of and their construction (ie hollow, solid, etc.)?

Rodney,
There are several potential problems with what you are asking about. As others have pointed out any increase in the stiffness will result in what is called stress concentration. There will be higher stress just in front of the stiffer area. Another potential problem is lowering the rods performance. Anything that you reinforce the ferrule with that has higher density than the thread and epoxy will add weight and lower the performance of the rod.

I have been thinking about this question and have collected some thoughts. I created a "picture" that I've posted to the miscellaneous section of the photo board. I'm open to corrections or omissions in my logic being pointed out.
Steve

[www.rodbuilding.org]

another component of the von mises stress that would result is due to the fact that when under load, the blank will want to deform nonuniformily, resulting in an oblong (oval) cross section. since the solid ferrule would not allow any distortion in the cross section, it will want to try to have a very abrupt change in cross sectional geometry, leading to internal stresses.

Steven,
I see a problem with your logic. The thread and epoxy are very high strain, very low modulus of elasticity, as compared to the graphite so they create relatively little additional stiffness. The additional stiffness at the ferrule is due to the reinforcing or the additional material that is added at the ferrule. And the stress concentration does not occur at the ferrule. It occurs just in front of the ferrule reinforcing, typically a couple of inches in front of it.
You are right about the cross section of the rod becoming slightly oval under a load. This is because for the rod to bend the portion under tension, typically the top of the rod, must become slightly longer and the portion under compression, typically the bottom, must become slightly shorter. And the top and the bottom of the rod resist this deformation. But the portion of the rod in the center, called the neutral axis, is not under any tension or compression, no stress or strain, it does not deform so the cross section of the rod becomes slightly elliptical.



Edited 1 time(s). Last edit at 04/20/2007 07:24PM by Emory Harry.

Steven. These blanks are made of graphite.

Emory,
Yes I agree that the thread/epoxy adds very little in terms of stiffness. Really I was only contrasting it's contribution to the effect of the adding a very stiff material to replace the thread. The lack of extra stiffness (in absolute terms) also points out that the load transferrence is through a different mechanism than shear flow through to the fibers of the butt section. I would argue that the transfer mechanism is through bending due to the stance produced by the overlap length. The requirement to maintain the integrity of the interface over the whole length of the insertion is why a warranty replacement of a broken rod requires that you send both the tip and butt sections back to the manufacturer. If you agree with this then it's even a stronger argument that the function of the thread wrap is to augment the integrity of the open (possibly flawed) end of the graphite skrim and why one must take care to prevent damage to the open end of the tip section.

Mark,
Fair enough. The proper design of a graphite layup can begin to approach the isotropic charactersitics of a solid material. There are many factors involved (e.g. fiber diameter, degree of bonding between sheets, orientation of the sheets, curing process etc) but it can be done. However, the beauty of laying up multiple layers of composite sheets is that the performance can be tailored to the expected loading conditions and desired response. My experience is with composite construction for wings of small aircraft where loading and load response factors are critical. Since rods need to perform equally in the loading conditions seen when fighting a fish, I would assume that the layup pattern is symmetric. If I were designing a rod to pull up a big fish straight up (e.g. deep sea rig), I might be tempted to add an extra sheet of longtitudinal fibers on the back of the rod. Unfortunately composite construction is susceptible to many seemingly minor problems. A small inclusion when glueing sheets will comprimise the function of the whole thing. Another real problem area is when an open end of a layup is expected to handle some form of loading (what is seen at the end of a female ferrule section in a rod blank). This means that many factors will possibly create the crack tip which leads to a zipper type failure. Again, this is why it is so important to have the wrap near the end of female section.

Steve

And I was simply trying to figure out if this would be a another way to dress up a rod in a unique manner.... Guess I will forgo trying out this idea. Thanks guys.

Rodney

Rodney,
Use thread as is typical, and then add your finish cover material with a slighly enlarged hole. Use a silicone bedding, which will allow flex without adding pressure. 1/16" should be plenty of clearance, and the silicone should do the rest.

Just a thought to help your idea work.

-TH