This is a question that surfaced recently and will likely need the expertise of those who know who carbon fiber cloth is laid out, rolled on the mandrel, and how the fibers continuity affect breaking strength.

I have have some no longer in production UL blanks which are quite exceptional in their strength to weight ratio. Thus, I don't want to accidentally destroy any if I don't need to.

The 8' blank is ideal for about 4-6 lbs test. However, it is routinely fished with 2-4 lbs test with very light lures such as minijigs. The tip is not as limber as would be ideal for 2 lbs test and very light jigs. The rest of the powerful body if just fine and allows excellent control of a fish. I want to sand down about 3 feet of the tip front, with more off on the last top 12 inches than the rest. however, I am afraid of weakening it too much.

Questions.

1. Would I be correct that the strength on such blanks comes from a CONTINUOUS strand of carbon fiber from butt to tip?

2. Then, if I sand and BREAK the continuity of the fiber, would it drastically reduce the strength of the sanded section? By this I mean that if I increase the FLEX of the tip by 30% for a given set load, the strength against breaking may be drastically decreased by more then 30%?

3. OR is the strength going to be PROPORTIONAL to the flex so that a 30% reduction in stiffness is generally corresponding to a 30% reduction in break strength?

We stressed stressed this blank with 5 lbs worth of weight at 45 degrees load and did not break. With 4 lbs test (max that it will be used with), the maximum drag it will encounter is about 1 lbs in normal fishing so there is a lot of excess capacity in its original form.

Some of the fibers do run from butt to tip but once joined in the prepeg and "cooked" they become part of the matrix and can no longer be thought of as individual fibers. You will no doubt note that the amount of carbon in the butt is greater than the carbon in the tip. Due to the flag patterns many individual fibers "run out" before they reach the tip. This is of no concern as again, they are part of the matrix as a whole.

The danger you run is really just one of sanding down far enough that you no longer have sufficient wall thickness to maintain good hoop strength along that area, or having such a quick reduction that stress issues cause the rod to fail. If you have no other use for the blanks you can always experiment.

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Tom, THANKS!! Your reply is exactly some of the information I am looking for.

Yes, the comment about wall thickness makes sense. I do have one blank that was crushed when a truck drove over it. I can cut the tip section into six inch segments and look at the thickness of the carbon fiber walls. Do you or anyone have a sense of how thin walls generally need to be to maintain hoop strength?

The only answer I can give you is that it needs to be "enough."

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Mo,
To answer your questions:
1.) Absolutely correct.
2.) Absolutely correct again. While it will certainly reduce the yield strength of the sanded area, it will also reduce the strength of the adjacent areas as well, although the initial failure will occur within the sanded area. I cannot verify the 30% breaking (yield) strength reduction given your parameters, but none the less it will be significant.
3.) It seems logical to assume the reduction in size/mass of the part to failure rate would be more algebraic than linier; a 30% reduction of material could produce a 40%, 50%, 87.3% (just throwing out numbers) higher failure rate.
As you mentioned, high-tech, modern-day composites rely upon utilizing the entire length of each and every fiber within the laminate to distribute any given load over the largest area possible. When the load is in only one direction, unidirectional fibers are employed; correspondingly, when the applied load is from numerous directions, unidirectional fibers are orientated at prescribed angles or woven cloth is employed. None the less, and in either case, THE ENTIRE LENGTH OF EACH AND EVERY FIBER IS CRITICAL, CRUCIAL AND RELIED UPON FOR THE UTIMATE INTERGRETY OF THE ENTIRE LAMINATE (PART)!!! PERIOD!!! Otherwise, we would simply be building fishing blanks, wind energy blades, stealth bombers and NASA spacecraft from short-fiber “chopper guns” spitting their goo into molds like typical boats and camper shells.
Bottom line is any sanding of a blank is treading on thin ice; I strongly advise against doing so!

Mark Talmo
FISHING IS NOT AN ESCAPE FROM LIFE BUT RATHER A DEEPER IMMERSION INTO IT!!! BUILDING YOUR OWN SIMPLY ENHANCES THE EXPERIENCE.

Thanks Mark. Helpful to hear. The trick is to sand and compromise some fibers, and then leaving other fibers intact. I did not mean 30% reduction in material but 30% reduction in power - so that when i get the same bend with 30% less weight, that's when I stop sanding. And I will be sanding in a spiral movement so that the outer layer of fiber is removed but leaving below surface fibers intact.

Anyone else sand blanks down?

Mo,
Consider your quest from another angle; why not simply find the proper blank to begin with and allow the fibers to do as prescribed rather than sand and jeopardize a sub-acceptable blank to accomplish such? At the risk of sounding rude, you may be taking on more than prudent, if not simple.

Mark Talmo
FISHING IS NOT AN ESCAPE FROM LIFE BUT RATHER A DEEPER IMMERSION INTO IT!!! BUILDING YOUR OWN SIMPLY ENHANCES THE EXPERIENCE.

I have sanded the tips of solid glass ice rods and ugly sticks but i wouldn,t touch a tubular rod of any kind..there is just not "enough" there to begin with..good luck..

Copy the comments from Ben.

As far as I am concerned, Never, Ever - sand down the tip of a hollow tubular fiberglass or graphite rod blank.

In a word - you sand the tip and you are asking for a failed rod.

The vast majority of the hollow tubular rods have a tip that is sized properly to carry the load that is then sent on down the blank for load dispersion.

Sand the tip, the tip gets weaker as you expressed in your comment. If there happens to be a rough spot - sure - go ahead and sand it off. Sand off any substantive amount of the tip and on down the tip section of a rod blank - Not my idea of a great idea.

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Conversely, if you have a solid graphite, carbon, or fiberglass rod - as are commonly used for ice fishing and also in the long rod style for plug version - absolutely go ahead and sand to your hearts content.

You may ask why. The simple answer is that I have sanded down the tips and tip section of hollow tubular blanks and of the many that I sanded down to try to soften the tip section - FAILURE of the blank every single time.

Conversely - I have sanded down many solid rod blanks in the tip area and I have never had a solid blank that I have sanded down break in the area where I had done any sanding.

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For your particular situation - go buy the blank of your choice the power and speed rating of the blank and build it up with your choice of components. ( To replicate Mark's comment.)

Happy rod blank - happy rod builder.

Take care

Agree with Roger. Never

Agree with Mark. Find the right blank. There are thousands of them out there.

At most i would sand off the finish if they are blanks that have a heavy finish coat on them, and even that I would have reservations about.

Maybe try experimenting with different lines to get the casting characteristics that you're looking for with those blanks. Not to mention going with a LARGER spool reel to increase casting efficiency.

Thanks all for your counsel and insight.

Mark, to answer your question as to why not just find another blank more suitable, this is literally a one of a kind design that I picked up years ago that is no longer available. I've not found anything that matches it in power to weight ratio and design.

Regarding sanding, some blanks are left 'raw' out of the oven, and others are sanded down smooth. I've had two identical blanks from the same company and it seemed obvious that one was sanded a bit more than the other and functioned just fine though it is slightly but noticeably softer in power. That's why I wondered about physically sanding a blank just slightly.

Thanks for all the replies. If I do try anyways, I will be very conservative. And if it blows up, I'll post on this thread. :)