Sewn loops in webbing

The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

qquake2k

Captain Low-N-Slow
Joined
Jan 26, 2010
Messages
13,574
Reaction score
65
I generally use nylon webbing as shock cords in my HP rockets, either 1/2" flat or 9/16" tubular depending on the weight. I've always just tied loops in it, but am wondering about sewing the loops. Is there any data anywhere about the strength of sewn vs. knotted loops?
 
And what kind of thread, nylon or polyester? I know nylon and polyester webbing is about the same strength, but polyester has higher heat resistance.
 
I use a bar-tacker....bought an industrial machine used on CL for a few hundred bucks....
(if you want to know what a bar-tack is, look at how the belt loops on your jeans are attached)
A few runs through the machine using Kevlar thread, I've got loops in my TN that are stronger then the native material....we break the TN itself before we break the sewing.
 
I use a bar-tacker....bought an industrial machine used on CL for a few hundred bucks....
(if you want to know what a bar-tack is, look at how the belt loops on your jeans are attached)
A few runs through the machine using Kevlar thread, I've got loops in my TN that are stronger then the native material....we break the TN itself before we break the sewing.

Yes, I'm familiar with bar tacks, but it wouldn't be worth it to me to buy a dedicated bar tacking machine. I have done pseudo bar tacks in the past with a close zig-zag stitch, but I don't know how strong they'd be.

I don't know of any hard data for strap, but knots reduce the strength of rope significantly.

When I sew my own bridles, I use polyester thread, but that's just what came with my awl.

That's great, John, I'll watch your video tonight when I get home.
 
According to parachute manuals, you should use 2, 3, or 4 point cross stitch pattern when sewing webbing together. The line of stitching across the web at the ends of a box stitch pattern actually causes a weakness in the webbing.

Here's page 186 of the Recovery Systems Design Guide. It explains it much better.
Capture.PNG

As for the bar-tack, as many belt loops that I've torn off jeans, I wouldn't trust it. The thread doesn't break, but it sure seems to weaken the material it attaches to.
 
I have had my wife do box stitches before. Now that I'm doing my own sewing, I use the multi-stitch zig-zag (usually two-row) as it's faster and more forgiving (looks-wise). I use Kevlar thread for both nylon and Kevlar webbing.
 
I use the diamond pattern as well. It's easy to do and it's very strong....and I learned how to do it by watching John's video on the topic.

The 28" long kevlar shock cord I made last night came out great.
 
According to parachute manuals, you should use 2, 3, or 4 point cross stitch pattern when sewing webbing together. The line of stitching across the web at the ends of a box stitch pattern actually causes a weakness in the webbing.

Here's page 186 of the Recovery Systems Design Guide. It explains it much better.
View attachment 252732

As for the bar-tack, as many belt loops that I've torn off jeans, I wouldn't trust it. The thread doesn't break, but it sure seems to weaken the material it attaches to.

Any idea of stitch length for the cross stitch patterns? And I know what you mean about bar tacks, I've always wondered about their strength. That's a lot of needle penetrations in a small area.
 
And what is the best way to sew the loop in the middle for parachute attachment?
 
And what is the best way to sew the loop in the middle for parachute attachment?
I fold the tubular nylon back over on itself "twice in Z-formation" with loop portion facing the nose cone. End result is three thickness of shock cord to stitch through diamond style. I figure the chute/drogue loop will carry more of the load than the nose cone/payload bay. Once the main chute pops out the force is again linear against the total shock cord length.
 
I'm not so sure about this. I bought some #18 needles, and extra strong Gutermann polyester thread. I promptly got a birds nest. I played around with the upper thread tension, and finally got it to sew. Because of the colors of the webbing, you can't really see the stitch pattern. Since the webbing is so narrow, I only sewed two straight stitches, with one diagonal stitch between them. Not sure how strong it will be. Once I get the other loops sewn, I'm going to hang the harness from a rafter and have my son bounce on it just to see if it will hold his not inconsiderable weight.

01_birds-nest.jpg

02_sew.jpg

03_sew.jpg

04_sew.jpg

05_stitches.jpg

06_stitches.jpg

07_loop.jpg

08_loop.jpg

09_loop.jpg
 
Since it was so hard to see the stitches, I drew a starting line on the webbing with a Sharpie. This will be the parachute attachment loop, so I had to sew through three thicknesses of webbing. The sewing machine wasn't happy about that. I finally put the upper thread tension on the highest setting.

10_line.jpg

11_sew.jpg

12_sew.jpg

13_birds-nest.jpg

14_tension.jpg

15_tension.jpg

16_birds-nest.jpg

17_tension.jpg
 
It absolutely would not sew in reverse, so I couldn't lock the stitches like normal. I ended up sewing forward, then turning the webbing around and sewing over the stitches, then turning it around again and continuing sewing. It did not sew very well, but the stitches seem tight. It will be interesting to see if this loop holds my son's weight. The only thing that gives me hope, is this particular webbing that I'm practicing with is very stiff and slightly thicker than the webbing I'll be using for the actual harness. I'm hoping the softer webbing will sew easier. It's also a solid color, bright orange, so it should be easier to see the black stitches in it.

18_birds-nest.jpg

19_loop.jpg

20_loop.jpg

21_bird-nest.jpg
 
Hey Captain, that webbing looks suspiciously familiar . . . aren't they your old suspenders that I saw you wearing a couple of launches ago?:lol:


It absolutely would not sew in reverse, so I couldn't lock the stitches like normal. I ended up sewing forward, then turning the webbing around and sewing over the stitches, then turning it around again and continuing sewing. It did not sew very well, but the stitches seem tight. It will be interesting to see if this loop holds my son's weight. The only thing that gives me hope, is this particular webbing that I'm practicing with is very stiff and slightly thicker than the webbing I'll be using for the actual harness. I'm hoping the softer webbing will sew easier. It's also a solid color, bright orange, so it should be easier to see the black stitches in it.
 
The softer thinner webbing is certainly easier to sew. I tried one long stitch pattern and two shorter ones. I think the two shorter ones work out better. After toying with the top thread tension, I finally got some decent stitches. Next I'll see if I can sew through three thicknesses of the softer webbing.

22_orange.jpg

23_orange.jpg

24_orange.jpg

25_orange.jpg

27_orange.jpg

28_orange.jpg

29_orange.jpg

30_orange.jpg

31_orange.jpg

32_orange.jpg
 
Hey Captain, that webbing looks suspiciously familiar . . . aren't they your old suspenders that I saw you wearing a couple of launches ago?:lol:

This is a little bit narrower than the suspenders. :tongue:

mork.png
 
I fold the tubular nylon back over on itself "twice in Z-formation" with loop portion facing the nose cone. End result is three thickness of shock cord to stitch through diamond style. I figure the chute/drogue loop will carry more of the load than the nose cone/payload bay. Once the main chute pops out the force is again linear against the total shock cord length.

Are you machine sewing or hand sewing with an awl?
 
I laid out the harness with the rocket sections, and marked where the chute loop should be.

33_harness.jpg

34_harness.jpg

35_mark.jpg

36_mark.jpg
 
I was able to sew through the three layers of this webbing with no problems. My stitches are looking better, but I'm still wondering how strong they'll be.

37_orange.jpg

38_orange.jpg

39_orange.jpg

40_orange.jpg

41_orange.jpg

42_orange.jpg

43_orange.jpg
 
Are you machine sewing or hand sewing with an awl?
I've been using the John Coker signature model of the Speedy Stitcher #250 awl.

Amazon for those reading along...

This is your best bet as it comes with the awl, needles, a pre-loaded spool of 40' of waxed polyester thread, and an additional 180 yards thread all for the current price of $18.29 (as of 1/25/2015): https://www.amazon.com/dp/B0049W6XRE/?tag=skimlinks_replacement-20

I have used both the Speedy Stitcher waxed poly thread and the Tandy waxed nylon thread. I cannot speak to the flame resistance of either because I use kevlar bridles long enough to reach outside of the airframe. Also have enclosed the stitching in heat shrink tubing (non-flammable) just in case.
 
Last edited by a moderator:
I've been using the John Coker signature model of the Speedy Stitcher #250 awl.

Just bought this yesterday at Harbor Freight, so I cannot vouch for how well it will work, but at $5.99 you can't beat the price. Unfortunately, there was another $92.00 worth of items my workshop could not live without :facepalm:

HF_SewingAwl.jpg

I guess I've read Qquake's signature one time too many

It's better to buy a tool than to be a tool.
 
Just bought this yesterday at Harbor Freight, so I cannot vouch for how well it will work, but at $5.99 you can't beat the price. Unfortunately, there was another $92.00 worth of items my workshop could not live without :facepalm:

View attachment 252957

I guess I've read Qquake's signature one time too many

It's better to buy a tool than to be a tool.

Heck, the thread alone is worth $5.99. The UK version: It's better to buy a spanner than to be a spanner.
 
Heck, the thread alone is worth $5.99. The UK version: It's better to buy a spanner than to be a spanner.

And, No shipping fees or waiting for it to arrive:)

Funny how we both posted that at the same time.
 
Back
Top