In this day and age of digi this and digi that, is there a simple inexpensive measuring device that measures relative thread pressure/tension/around a cylinder, such as a rod blank, or a fishing fly hook, by a pre-test around the device?

I'm reading that thread tension for wraps should be some unknown force, just enough tot hold the guides, etc. This is the secondary application for the request.

The primary would be in fly tying. I do a beginners class for adults each winter, and thread tension cannot be taught. It must be felt.
And to a student, not one of them has easily grasped the concept of maximum thread tension.

I can move the entire fly rearwards on the hook, just like a tarpon fly, their work is alweays that loose. For whatever reason, they always get offended at the destruction of their work. Pity.........

I always stress what's the point of cloning a fly that falls apart just like the cheap imports, when with a little tension, all that goes away.

Back to rod guides: It's not as important here, as there is either too little tension, too much tension, or acceptable tension.

But it sure would be nice to actually measure the cumulative pressure around the blank with X number of wraps of size A-EE thread at X grams/ounces/pounds of tension.

I would think any of the digital fishing scales would serve the purpose

I think you are in error, Robert.... I mean the tension on the project, not the tension on the thread. Example: I can apply size A thread very loose, areound the project, exerting zero tension over a 3 inch wrap, so it just habgs there, or I can apply the thread just under the breaking point over a three inch wrap. I would suggest if I applied size A thread at just under the breaking point over such a wrap, it would be a bit to tight... in rod building, as I said, not a problem... either ok, too loose, or too tight.
I do not know mechanics of physics, but it seems reasonable to assume that over a 360 degree circle, and a pound of force thread tension, exerted over every degree, would I not have 360 pounds of force over the circle, not just the one pound thread tension ?

There is too tight, too loose, and just right. The Goldilocks & 3 bears of thread tension. I totally agree that it cannot be clearly shown, but felt.

You're quite right in your 360 degrees of force thinking. You actually get the 1 lb of tension translated into the thread shrinking to it's normal length (it has stretched) and thus compreesing the guide foot onto the blank. You'd probably get just a small portion of the 1 lb thread pressure actually translating into compressive stress on the blank.

Wow ! Another fascinating attempt to quantitate a commonly used force. I wish my college Physics or Statics (that's 'statics', as in static v. dynamic forces, not statistics) had covered that explicitly. But I wasn't in Mechanical Engineering, so, it didn't.

Anyway, it seems that the maximum compressive force for each strand of thread would be the tension in the thread divided by the area of the thread strand covering the rod. Taking the sum the entire wrap at the guide-foot would probably give an expression something like:
Pressure (PSI) = (thread tension in lbs) * (# of winds) / (area of the wrap cylinder)
Wrapping or Strapping Force = (thread tension in lbs) * (# of winds)

Imagine this: Draw a simple, single pulley, and drape a rope over it. Tie one end of the rope to a stop on the drum, and don't allow the drum to rotate. The maximum force directed toward the center (which is the compressive force we want to measure) could not exceed the tension in the rope. It may depend to some extent on the stretch factor in the rope as well, as suggested by Ted Morgan, but that is not a variable independent of the tension, so as the ole profs say, "we'll just ignore it." Perhaps there is a trigometric function which serves as a coefficient of the maximum force - my intuition would guess it to be 0.5, because of the two free ends of the rope.

Well, by now. I am probably just talking to myself, eveyone has grabbed that beer and is saying, "Yeah, let's get back to that part where we say, 'We'll just ignore it !'."

So, here's one man's honest attempt to come up with a formula for
calculating something that is commonly used, but taken for granted. Using a spring scale to measure the tension isn't too hard. But converting that into PSI for a wrap is a very interesting question. Any mechanical engineers out there? ...

Cliff Hall, chemical engineering flunkie from the Univ. of Florida, Gainesville.

Mech Eng student here!!!! Interesting. I immediately thought "oh boy, you nerd" when i responded. Ignore the extras for sure!!

However, it's like detecting light striking fish. It's all about feel. We want to be a ble to reposition a guide if we get it wrong without cutting it off most of the time (usually after you crank out the best guide wrap ever!!) Same with destroying your student's flies.

When hand wrapping, too much tension for me is when I cannot spin the blank by just rolling my palm on it with just a little pressure (back to feel!).

P.S. - Well, if my conceptualization of the problem and derivation of a
valid equation are faulty, maybe I can just chalk it up to 5 days of cabin fever from Hurricane Frances. Talk about feeling tied down !! Between all the wind & rain & downed trees & power outages & closed businesses & night curfews & unsafe driving conditions, I am ready to ponder anything that will focus my mind on something other than the relative helplessness that we have had around here in Gainesville, FL since Thursday.

So, does anybody know an equation for the solution to this problem,
or is this just so much 'dust in the wind'?

There used to be applications for the Piezo-electric effect: conversion
of the mechanical pressure on a certain crystal into a measurable electric current. I think that is the basis for most of our modern-day,
single-pan, top-loading, small-capacity weighing scales (0-500 grams). But I don't think we are going to find a tubular configuration at Lowe's.

I can't imagine that the rod blank manufacturers do not measure this on new blank designs. Isn't it called "hoop-strength" or something akin to the constrictive crush force, a bit like the crush-depth for a submarine?
Clearly, no one can generate that kind of force before the standard
thread would break. But when working up a new blank design, some
technician must have to make sure that the blank wall is strong enough not to collapse under an extremely tight and overwrapped rod guide.

Alright, now I think I'm wound up too tightly over all this.
I'll give it a rest. Happy rod-wrapping to you all ! Cliff Hall .

You analysis of one pound of tension around a one inch rod resulting in 360 pounds of tension is incorrect.

The measure of tension would be a tangent at any point on the circumference of the rod. Again if you took some scales and measured around the circumference, you would find that one pound of tension produced one pound of tension at any point.

Imagine this --- take one loop around the rod, and tieing off one end to a hook on the ceiling, and hanging a one pound weight on the other end. If you pull at any point around the circumference with a force of more than one pound, the weight will rise ( allowing for friction forces) So the force at any point is one pound, not the sum of the degrees, which in truth would be infinite. If you pull down on the rod itself with a force greater than one pound, the rod will move.

Even if you take several loops, and the tension remains constant, it will be the same at any point -- in this case 1 pound. What comes into play is friction forces, primarily of the thread against itself. At some point the combined friction forces will exceed the tension. Note that in fly tieing the thread is usually locked mechaniically with a knot and in rod building the thread is locked with friction by pulling the tag end under enough threads to lock it all into place with friction.

it seems as if you want to know the resultant force from wrapping rather than the tensile force from "pulling" the thread around a cylinder. the force is applied tangent to the cylinder, the only real shear forces inherent to wrapping is by squeezing/stretching the thread to wrap. it then reaches an equilibrium (like putting a rubberband around something, if you stretch it, and then just place it around and object at intervals with one end pinned, it will strangle it with the same force as if you put tension on it to stretch it out while winding).

steve

All the physics aside, some sort of tension measuring devise would be nice to have. I still have doubts about what the proper thread tension should be under any given circumstance, and am still not sure if any of my wraps are the proper tension. I hear "not too tight or you may damage the blank" or "not too loose the guide may not hold properly." Without having failures in my wraps, how can I be sure the tension is correct? Some sort of standardized tension devise that could be used universally by rodbuilders would be nice, and I don't really see that it would have to be something very complicated.

What do you use to create the thread tension while wrapping? A heavy book, or torque against the endplate of a spool? Actually, in the end it is immaterial, as long as it is reproducible and constant.

Under the conditions identical to your actual wrapping a rod, just use a typical fishing spring scale to measure the tension against your drag device. Then you can decide for yourself based on your own experience what seems to be the proper tension. You can adjust the weight of the books or the torque on the spool plate accordingly. A tension sufficient to hold the guide in place while being stressed is the principal issue. Any tension above that is essentially overkill. And obviously there is a wide range of tensions within which no problems develop between the time of wrapping and of being abused while fishing. I don't think there is much danger in applying so much tension to the thread while wrapping that the rod blank will be crushed.

From the Gudebrod catalog - Tensile Strengths for Rod Thread (# = lbs):
Regular Nylon Thread A = 2.7#, D = 7.4#, E = 11.6# .
NCP Thread: A = 2.2#, C = 4.6#, D = 5.1#

I too am a stickler for details and a uniform technique, so as to generate a consistent & reproducible product. But I keep hearing a little voice inside my head reminding me that, "If it ain't broke, don't fix it." and "Leave 'good-enough' alone." As long as the thread is not breaking and the guides are not slipping, that tension is adequate. Use it consistently, even check it with a spring scale for each wrapping set-up or adjust for different size threads. But in the end, whatever works for you is likely to be all the quality-control you'll need.

Thanks for this lively discussion, - Cliff Hall in Hurricane-land Florida

Do a search for: CC for thread tension and click on the first answer to come up, then read the threads. This will not answer your search for a scale to read the pounds & ounces or psi or whatever, but it will give you an indication of how much tension to set your thread tensioner to. Also, in flytying, you can set the thread bobbin to a similar tension and tighten up jour student's flies without having to teach them how to feel how tight they need to wrap the flies for durability. Ralph

Thanks to all who contributed....what I began to do to demonstrate thread tension, is have the student hold out his little finger on his non-tying hand, and request the student to wrap his thread about 20 wraps at what he considered max. tension. Pretty well everybody made 20.

Then I took his *other* pinky and did likewise. Their eyes popped, and they requested I stop well short of the 20 turns. Most strongly requested I stop at turn 5 or 6. (One guy toughed it out to turn 12.)

I remarked that's tension, dude....that's where you want to be. :-)

Whereas I supply the tying thread in the class, I guess the tests are ok fair, as it's all Canadian (Unithread) 3/0 unwaxed.

I do have a slight advantage over the class, though, my bobbin is a USA-made (Rite Bobbin) fully adjustable in approx 1/4 ounce increments, and theirs were wish-bone style, adjustable by bending the arms, and by palm pressure.

Thanks again. KD