ff string question

[Big Dave]

OK This is probably a stupid question but I've only used  B50 string. Are there more than one type ff string material. If so do some of them stretch more than others? I was wondering if there is a type of string that stretchs a little but that you can get a smaller dia. string than with B50      

[NW]

Yes, yes and yes.
I'm not the expert, but I like Dynaflight 97, and TS-1

[Mr.Magoo]

Lots of different "FF" materials.  Most don't really stretch, they tighten-up and the slack in the twist is taken out.  Most are also smaller diameter than B50.  D97 was on sale when I bought string, so I use D97.

[JImmyDee]

Types?  FastFlight is made from Spectra which is the same stuff as Dyneema: a polyethylene.  As far as string-making material is concerned, the biggest difference I see among various products is the amount of wax added to the fiber.

Stretch?  Hmm...  As pertains to strings, the nerd term is elasticity -- meaning the material will deform under stress but return to it's original shape.  Dacron is elastic.

The various FastFlight materials are not elastic.  They do, however creep - deform for as long as you stress them and don't return to original shape - but the stresses we subject them to aren't enough to cause creep.

Spectra and Dyneema strands are smaller than Dacron.  Most resellers recommend more strands than are necessary in order to make a string that's as big around as a Dacron string would be -- and sell more material!

I don't use more strands; I use a larger diameter serving material.

[Big Dave]

Thanks for the info      

[md126]

hi big dave.....different types of "FF" but DF-97 and TS-1 are the best imo. i had a little more stretch/creep w/ the DF-97 but it was minimal. i also think the TS-1 came pre-stretched by the maker.

that being said i prefer good ole'dacron...  

[JImmyDee]

I've got to admit: I'm confused -- but I don't feel alone.

I was talking to a friend and *he* said that he had seen "stretch" numbers - as a percentage - for Dacron (3%), Dyneema (1%), and Spectra (under 1%)  but he didn't know exactly what was meant by "stretch."  Does anyone else know?  Or know what website he might have been talking about?

[JImmyDee]

If you haven't had enough of this...

I did two things: a redneck engineering experiment and some web research.

I took a single strand of Dyneema '02, marked off 50", and used it to hang a 45# weight.  (The toughest part: finding a knot that wouldn't slip!)

As soon as the weight was hung, and while the strand was under tension, I measured the distance between the marks as 50-1/4".  I took the weight off and the marks were still 50-1/4" apart.  I put the weight back on.  Several hours later, measured under tension: still 50-1/4" -- maybe a tiny bit (the width of the mark drawn with a ballpoint pen) more.  So: I saw 1/2% elongation.

I found some guys thesis on the web.  One chapter dealt with elongation of polyethylene fibers.  His  thesis included this diagram
which depicts three phases of elongation vs. constant stress:
I. increasing at a decreasing rate,
II. increasing at a (virtually) constant rate, and
III. increasing at an increasing rate (quickly resulting in failure.)

Phase I doesn't last long - he measured it in fractions of a second.

His conclusions were interesting:
- Phase I includes reversible (elastic) and irreversible (creep) elongation.
- Phase II consists entirely of irreversible (creep) elongation.
- The reversible elongation is miniscule compared to irreversible elongation.

The differences from one brand to another?  There have been at least two varients of Dyneema and Spectra: Dyneema SK60, Dyneema SK66, Spectra, and Spectra 1000.  Although made of exactly the same molecule, the differences between the finished products are trade secrets -- but it seems that the differences are the number of filaments per strand (hundreds) and the technique used for drawing the strands during the manufacturing process.

Then, of course, the folks who resell the material as bowstring making stuff add whatever wax they think belongs on the product.

Now, you know what I know...

[joe skipp]

I've used both Dynaflyte 97 and T1. Right now my preference is the T1.

[BigRonHuntAlot]

Another TS-1 Fan.