Properly calculating stitching strength

[iconicflux]

I have a lot of experience with sewing webbing straps (I'm a hammock camper that makes their own gear) and as a result I've done LOADS of research on how to make the strongest webbing straps. I've seen some projects on here that I feel could have used some of the knowledge so I thought I'd pass it on...

Properly calculating the strength of stitches (and how many inches of stitching are needed for a given strength) is done as follows:
1. Get a thread and research the strength of the thread. The Gutterman thread that I normally use has a breaking strength of about 8lbs per stitch.
2. Decide on the stitches per inch. I normally use 10-12 SPI but I may do up to 14 if the material is high quality and thick enough.
3. Calculate the strength for one inch:
SPI * thread strength * 1.5 = (so for my usual thread it's 12*8*1.5=144lbs per inch)
4. Calculate the number of inches of stitching needed (say I want 1500 lbs breaking strength):
1500/144=10.41 inches
5. Decide on the stitching pattern... not all are created equal. In general you want to use that 10.41 inches which may look like a box of 2"x1"x2"x1" with a V in either direction in the box kind of like [<>] but if you really want to increase the strength having smaller boxing at either end like []XX[] is quite a bit stronger. If you want some info on a study of the strongest stitching patterns let me know and I can find it. The important thing is that you use the 10.41" no matter which way you use it.

Also, keep in mind that your stitching strength will never be stronger than the breaking strength of the material. It doesn't matter if you have 1500 lbs in stitch strength if the material/webbing will only hold 300 lbs.

Hopefully that's helpful to y'all... stay safe out there.

 

[sojourner]

I want to get a thread injector and make some life supporting sewn straps, saddle, etc. ... problem is, I am OCD. I want to have this nailed down to a science before trusting my thread injected saddle will keep me from an unanticipated free fall.

This is good information. What I am curious about is how the professionals get to be that way. Is there some type of certification that someone needs? Do they have to apprentice for a time under an expert? How about too much stitching? Will it be so much that it degrades the performance of what is being stitched?

What would be really cool is to have some kind of a podcast with a luminary of stitching life supporting saddles, like Casey Jones of New Tribe / AeroHunter. And getting more info. about what is needed to properly do life support stitching.

Again, thanks!

 

[bj139]

On the break tests I have seen it either breaks on the single ply material beyond the stiches or the stiches break.

 

[MettBriler]

thanks for the info, is there anyway to break test these extremely high strength stitches? thinking about making a saddle, but would feel more confident making two and destroying one to see when it breaks.

 

[iconicflux]

There are a few ways of testing it. If it's something like a webbing strap you can tie it to something that can hold 40 lbs bags of pellets (or 80 lbs bags of concrete) and then just start piling the bags on there.

The best way is with a force gauge but unfortunately the ones that can do 2000 lbs are like $1100.

thanks for the info, is there anyway to break test these extremely high strength stitches? thinking about making a saddle, but would feel more confident making two and destroying one to see when it breaks.