Simple webbing pull test

FreeFallin

FreeFallin

Branched out member
Location
Wisconsin
Hi all, I know TS offers this service but I am checking to see if anyone on here has a less official (free) method of testing break strength up to 5k lbs. I don't need it to be exact, just ball parky.

I am experimenting with some machine sewn webbing for non life support use. After a lot of research and the simple tests I could perform myself, I have 3 small 12" long straps made fron 1" climbing spec webbing. There is a matching loop sewn on both ends of each strap.

Each strap has the loops connected using a different sewing pattern. I just need to know how many pounds to break each of the 3 straps, and where they broke (stitches, mid-strap, end strap connection point, etc.).

I could try using a single strap to hang both of my vehicles together in an oak tree, but my wife keeps saying that seems like a bad idea, anyone have a better solution before I cough up the testing money?
 
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A bigass ratchet winch and a scale... but I don't know where you'd get a 5k scale... GoPro or similar camera on a tripod, pointed at the scale, to record the break point.
They make the winches that big, I have seen them at farm stores (TSC, Orsheln's, etc.) but they weren't cheap.
 
That would be cool, let me know, it's only three pulls so I can validate my thinkin' on thread strength, stitch strength and patterning.
 
I was thinking the hanging type scales like you weigh a fish with. I have a 500-lb. analog one, and I've seen a digital 1100-lb. one (both for pretty cheap, I think I got the 500-lb. one at Menard's for about $25). Of course, those aren't big enough. There's gotta be a 5,000-lb. one out there that doesn't cost hundreds of dollars, right?
 
Is it possible to just sew 1/5 of the number of stitches you originally wanted to test to 5000 lbs., and only test to 1000 lbs?
 
I think that would be valuable if I didn't already find some great bench marks for thread and stitch break points in webbing.

If you are interested in the gritty details, here you go-

[Edited]
I am using #69 T70 bonded nylon thread (the thickest my machine can handle) sewing through 2 layers of 1" climbing spec tubular webbing. There are some well documented tests out there that people from other disciplines have put up on the Web and I am fairly confident in the single stitch breakpoint being between 15-19#. Mathematically it should be between 18-23# but I am estimating low to account for variables like thread inconsistencies, and the depth my machine is capable pulling each stitch back up through the webbing. This is where non-commercial machines struggle. If I could get enough thread tension and motor strength to bury each stitch in the middle of the material I think the breaking strength would be closer to the ideal 20# per stitch.

If you are still reading this :sleep: then the thing I need to test now is the stitch pattern for optimal strength. This is not as big a concern for manufacturers since commercial machines can handle #138 and thicker threads where you mainly need to pass a minimum stitch count to pass the webbing strength. This is why you see anything from bar tacking to boxes with an X on your harness, they can do what they like when each stitch can hold 50# on it's own.

With lower strength threads it can still be done but the pattern becomes more critical since over saturation of stitching will weaken the webbing, and patterns with exposed outlying stitches tend to tear those first, weakening the pattern, and failing with a lower force.

If you are still with me, my challenge is to sew the right number of stitches, in a pattern with maximum hold that doesn't weaken the material.

Others have demonstrated that one pattern that shows promise is several lines of straight stitches running horizontally down the webbing the same direction as the webbing threads. This leaves the webbing a little ply-able but meets the minimum number of stitches, but this leaves the ends of the stitch rows exposed to additional force when under load.

One idea I have not seen data on, is whether bartacks alone are as strong, as a pattern with bartacks on the ends, and straight horizontal lines in the center.

I also have an untested theory that bartacks made from lower strength threads like mine fail sooner because there is more stretch at the edges of webbing when it's under load vs. the center, and the stitches at the ends of the bar get more pull and start to fail. If this is true, then curved bartacks would meet the load more evenly and fail later.

This is what these 3 unscientific pulls will lead me towards.
 
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JeffGu said:
I was thinking the hanging type scales like you weigh a fish with. I have a 500-lb. analog one, and I've seen a digital 1100-lb. one (both for pretty cheap, I think I got the 500-lb. one at Menard's for about $25). Of course, those aren't big enough. There's gotta be a 5,000-lb. one out there that doesn't cost hundreds of dollars, right?
Click to expand...
I'd bet if you pulled to the point of failure on any type of spring gauge the rapid unloading of the spring may cause it to lose its calibration.
 
tc262 said:
...pulled to the point of failure...
Click to expand...

I don't doubt that a bit, for one that would handle 5k lbs... my little 500 lb. one, I've overloaded a few times trying to weigh logs. It doesn't seem to lose its mediocre calibration (I weigh myself with it, and compare that to a digital bathroom scale) by more than a few pounds, but then I'm not putting anything like 5k lbs. on it. It's not too accurate, anyway, at either end of the scale... but pretty close in the center half of the range. It was also $25 so I wasn't really expecting much from it.

What's the max limit on a Rock Exotica load cell? Seems to me they're not in the 5k range, I'll have to look that up, or just let Frank answer. I'm pretty sure he has one... or five.

:inocente:
 
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