Nylon cordage vs HMPE?

[RokJok]

For sewing or lashing thread/cordage, does anyone have experience using or testing nylon fiber vs HMPE or ultra-high molecular weight polyethylene (UHMWPE) in sheath making? Reason I ask is that HMPE is supposedly more abrasion resistant than nylon. Or is the difference in actual usage going to be so small (or at such extremes of stress) as to be a mere academic numerical exercise.

In my limited experience, braided nylon, mostly paracord & kernmantle braided very small diameter rope, seems to knot better than polyethylene due to being more pliable, compressing more & having apparently more friction inside the knot. The poly seems stiffer & very slippery. That slickness & tendency to unwind would make it a poorer fiber choice for sewing thread. I recognize that braiding/twisting/laying method & surface finish can influence this to a fair degree.

Also, when flame is applied, nylon melts together to readily form a balled end on paracord whereas the poly rope I've found wants to shrink back from the flame. That makes it harder to seal the ends of a poly rope.

So the other question is: what thread do y'all use in sheath making?

TIA and I appreciate any & all input or enlightenment the craftsmen in the crowd can offer.

 

[gadgetgeek]

I only know those materials from other fields, but nylon has stretch and so can hold some tension, or adjust, where the others basically do not, which in some fields means the line taking the strain and not walking out under cyclic loads. As you mention, nylon melts, PE does a little, but mostly just degrades. It also does not like knots pretty much ever (see cyclic loading). This could be worked around in stitching, but I don't know why you'd want to back stitch that much. I'd suggest that for thread, waxing the nylon would protect it to a fair degree, likely to make it abrasion-resistant to a similar degree to the other materials. UHMWPE is really slick, I've used it in low speed bushings, and my dad has a legendary toboggan made out of a sheet of the stuff that is like throwing eggs on well oiled teflon. That said, if you can get enough contact patch, it will lock onto itself if you have a hollow braid and you can splice into that, either a brummel or sliding splice. But for stitching, that seems, like a lot of extra effort. The dyneema I've used (lash-it) is coated to help it knot, but those knots are accepted to be of low pullout force in general.

If you wanted water resistance and were willing to back-stitch a lot, then UHMWPE might have some advantages, but its such a pain to work with that you are likely not gaining much with the cheaper and easier to work nylon.

 

[Horsewright]

Many leather workers swear by nylon thread. Just as many swear by poly thread. I've used both and don't see much difference although I've seen certain stitching machines prefer one to the other. I use nylon and have for years although I have experimented with poly years ago. I make a lot of stuff, with lots of it being used very harshly and thread wearing out or breaking doesn't seem to really be a deal.

 

[gadgetgeek]

That brings up a good point, nylon has a few different molecule sizes, but overall, its a pretty narrow window, whereas it's my understanding that PE can have a very wide range of molecule length and consistency, so I'd bet that you might see a wider range of performance just in PE and you do in nylon. My mind initially had gone to dyneema and its variants, polyethylene comes in a lot of flavors, and so who knows what a particular thread is made of. In the world of climbing and rigging the big factor is batch consistency, as well as how consistent the molecule size is within that particular product, as that range does seem (although testing is pretty challenging) to have an impact on the behavior of the end product. When talking about thread, I'd guess that a lot of that gets minimized as there are fewer thread makers than rope makers. And as Horsewright stated, I wouldn't be shocked at all if some machines preferred nylon over PE, or the reverse. I mean, no one is running 1.7mm zing-it in a needle machine so my experience there is limited to cotton twist and polyprop.
I mean, I would think that overall sheath design would play a bigger factor to prevent the edge from hitting the threads inside, so a good form, or a well placed rivet would make far more difference than the thread. I'd guess for most users here, their edges are good enough that if the knife itself is contacting the thread, the HMHW PE is going to last a hair longer, but only because it's doing just as much damage to the edge.