|
|
Forums:
Climbing Information:
The Lab:
Re: [AeroXan] bar tack failure:
Edit Log
|
|
moof
Feb 11, 2008, 8:45 PM
Views: 21272
Registered: Oct 17, 2003
Posts: 400
|
Even though some home grown samples outperformed professionally bar tacked ones doesn't mean we should all go sew our own of course. The difference between 5 and 6 tacks is likely a red herring. Without getting a larger sample size, the results are mostly just "interesting" To compare joints you would want all the slings sewn/tied off of the same rolls of webbing.
Professional ones usually go through batch testing, and get a 3 sigma strength rating. If you just cobble to together at home, you have no guarantees, and no control.
I sew a lot of NON-life support, non-full strength gear for myself and others. Lately it's been Russian Aiders, which have to be strong, but are not holding falls, or acting as the sole life support like a harness. From all of this I've become keenly aware that a few bar tacks would take a couple second, while it takes me ~5-10 minutes per zig-zag joint to laboriously go back and forth. Mine are also all unique. Even though I have tons of stitches such that I know they are strong, I can't ever claim an average or 3 sigma strength without both testing them AND having a very repeatable pattern (ie, not done by hand).
At the first order, say just putting in a dozen stitches the literature says you get about 1.8X the threads tensile strength per stitch (due to loading in shear, and there being two strands of thread in cross section). So the first order approximation for on my my 2" joints with about 250 #69 (11lb) stitches is ~5000 lbs. Reality is that once you approach the strength of the webbing there are other phenomenon that kick that determine the overall strength.
(This post was edited by moof on Jun 20, 2009, 3:38 AM)
|
|
|
Edit Log:
|
|
Post edited by moof
() on Feb 11, 2008, 8:50 PM
|
|
Post edited by moof
() on Jun 20, 2009, 3:38 AM
|
|
|
|
|
|
