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Quagmirian

Base rig project

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On 12/21/2021 at 6:42 AM, wolfriverjoe said:

I have nothing to contribute to this discussion from a technical standpoint.

But I want to comment that it's absolutely amazing to see folks with decades of experience in this sort of thing freely contributing and sharing to help the 'new guy' get it right.

This is basically 'doctorate level' harness design and construction stuff.
Both theory and practical.
Way, way, waaaaaaay beyond my skill/experience.

But the fact that Jerry, Lee & Rob are willing to help at the level they are is REALLY cool. 

Hi Joe,

Here is something an old rigger taught me back in the mid-60's.  His name was Eddie Brown and if you were a rigger on the west coast back then, you knew who he was.

He taught me how to calculate the strength of a stitch pattern.  Let's take a typical 3" long, 4-point stitch pattern.  A 4-pint stitch pattern is 8 legs of stitching.  This is easily seen on the harness ring attachment on a Vector, Infinity, etc.

1.  The thread has a strength of 45 lbs.

2.  You should assume 5-6 stitches per inch; let's use 5.5

3.  You should discount your calculations by 15% due to thread damage as it passes thru various places on the sewing machine & thru the needle; the needle does the most damage to the thread.

Therefore, a typical 3" long, 4-point stitch pattern gives us:

45 lbs x 3" long x 5.5 SPI x 8 legs of stitching = 5940 lbs / 1.15 (our 15% reduction) => 5165 lbs total.

Just a little historical info for you.

Jerry Baumchen

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I'll expand on that with some caviots. Perfectly good model but like most models it breaks down when you try to extend it into the range where the systems behavior becomes nonlinear.

 

That kevlar thread is actually stronger then the nylon tec 500. Sew loops at both ends of a peace of kevlar webbing one with the stronger kevlar and the other with nylon. Pull. The kevlar will break first every time. The nylon junction is stronger not by a little bit but by quite a lot. So on places that are protected and not subject to aerodynamic heating we use nylon where we can. The little bit of give in the nylon let's it share the stress more evenly over the stitch pattern.

 

As you try to get more strength, more stitches, in a joint there is a point of diminishing returns where when you pull on it only part of the stitch pattern bears the load. So the pattern breaks progressively from one end to the other. This relates to the elastisticy on the webbing. It is exaggerated if there is a discrepancy between layers of webbing. Say there are three layers and you are pulling on the top layer. The bottom two layers are stiffer then the top layer. When the top layer stretches it loads the first part of the pattern those stitches break first.

 

Some one once told me that a reinforcing, like a tape on a canopy, should have an elastic coefficient a certain percentage of the substrate to avoid point loads and shear forces between the two. In the same since the stitch pattern must have the ability to stretch and deform to match the material being joined. That is why it's advantageous for the stitching to be as far as possible angled relative to the load. Notice that most of the stitches in a 3 or 4 point are angled. When you pull on it the highest load points are at the corners where the side stiches are straight. This is actually less then ideal. In fact the straighter the stitches the higher the load at the points.. So there is kind of a minimum angle that you would like to maintain in the pattern. Therefore there is a limit as to how long you can make a three or four point or the number of points you want in a pattern. So if you want a larger longer pattern it can be better to dubbel or triple the pattern. Imagine two three points end to end. Now imagine the stitches continuing rather the turning where the points meet. Basically the pattern bounces back and forth from side to side of the webbing like a big zigzag. Think of the dot in the old pong game. Try drawing it you will have an over sew when you get back to your starting point to move to the next half of the pattern. You'll wind up with the same amount of over sew as you would have in an equivalent pattern. But a multipattern can be better then one long four point. The maximum length of the pattern tends to depend on the stiffness of the webbing.

 

The most extreme example of shortening and widening the pattern would be to sew it in a diamond pattern like to sew the four point sideways on the webbing and I've seen this in some heavy load applications on nylon. They actually sewed it back and forth from side to side in a big square block. It defenintly let the nylon stretch but a don't favor this because I think you would tend to snap the webbing at the end of the pattern. But I have seen it done.

 

Most extreme example I've run into. An early project I was given was to test seam designs for a prospective canopy. So I had to figure out a way to load seams to destruction in f111 and zp. Trickier then it sounds. Wanted to load a decently wide area. Clamps didn't work. When the fabric stretched under load the fabric it self would tear under shear at the sides of the clamps. Ultimately I wound up sewing leaves of wide webbing to the fabric to pull on. It was an interesting stitch pattern. Boxes, 3 points, 4 points won't work. Any thing with a straight corner would cause the same shear as a clamp and tear the fabric before the seam. It needed a smoother transition to the unloaded fabric. I wound up with a two point with the points in the middle of the pattern not at the edges let the fabric avoid that sudden shear load. I don't like to think about how many of those test articles I had to sew up.

 

Lee

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I'll expand on that with some caviots. Perfectly good model but like most models it breaks down when you try to extend it into the range where the systems behavior becomes nonlinear.

 

That kevlar thread is actually stronger then the nylon tec 500. Sew loops at both ends of a peace of kevlar webbing one with the stronger kevlar and the other with nylon. Pull. The kevlar will break first every time. The nylon junction is stronger not by a little bit but by quite a lot. So on places that are protected and not subject to aerodynamic heating we use nylon where we can. The little bit of give in the nylon let's it share the stress more evenly over the stitch pattern.

 

As you try to get more strength, more stitches, in a joint there is a point of diminishing returns where when you pull on it only part of the stitch pattern bears the load. So the pattern breaks progressively from one end to the other. This relates to the elastisticy on the webbing. It is exaggerated if there is a discrepancy between layers of webbing. Say there are three layers and you are pulling on the top layer. The bottom two layers are stiffer then the top layer. When the top layer stretches it loads the first part of the pattern those stitches break first.

 

Some one once told me that a reinforcing, like a tape on a canopy, should have an elastic coefficient a certain percentage of the substrate to avoid point loads and shear forces between the two. In the same since the stitch pattern must have the ability to stretch and deform to match the material being joined. That is why it's advantageous for the stitching to be as far as possible angled relative to the load. Notice that most of the stitches in a 3 or 4 point are angled. When you pull on it the highest load points are at the corners where the side stiches are straight. This is actually less then ideal. In fact the straighter the stitches the higher the load at the points.. So there is kind of a minimum angle that you would like to maintain in the pattern. Therefore there is a limit as to how long you can make a three or four point or the number of points you want in a pattern. So if you want a larger longer pattern it can be better to dubbel or triple the pattern. Imagine two three points end to end. Now imagine the stitches continuing rather the turning where the points meet. Basically the pattern bounces back and forth from side to side of the webbing like a big zigzag. Think of the dot in the old pong game. Try drawing it you will have an over sew when you get back to your starting point to move to the next half of the pattern. You'll wind up with the same amount of over sew as you would have in an equivalent pattern. But a multipattern can be better then one long four point. The maximum length of the pattern tends to depend on the stiffness of the webbing.

 

The most extreme example of shortening and widening the pattern would be to sew it in a diamond pattern like to sew the four point sideways on the webbing and I've seen this in some heavy load applications on nylon. They actually sewed it back and forth from side to side in a big square block. It defenintly let the nylon stretch but a don't favor this because I think you would tend to snap the webbing at the end of the pattern. But I have seen it done.

 

Most extreme example I've run into. An early project I was given was to test seam designs for a prospective canopy. So I had to figure out a way to load seams to destruction in f111 and zp. Trickier then it sounds. Wanted to load a decently wide area. Clamps didn't work. When the fabric stretched under load the fabric it self would tear under shear at the sides of the clamps. Ultimately I wound up sewing leaves of wide webbing to the fabric to pull on. It was an interesting stitch pattern. Boxes, 3 points, 4 points won't work. Any thing with a straight corner would cause the same shear as a clamp and tear the fabric before the seam. It needed a smoother transition to the unloaded fabric. I wound up with a two point with the points in the middle of the pattern not at the edges let the fabric avoid that sudden shear load. I don't like to think about how many of those test articles I had to sew up.

 

Lee

20211222_153024.jpg

20211222_153012.jpg

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On 12/21/2021 at 11:49 AM, Quagmirian said:

The way I'm stacking the layers is leg strap on the bottom, followed by a MLW layer, then the other legstrap layer, then finally the second MLW layer on the top. That's the way it is on the one I'm copying.

I do read everything that's written here but I often just go away and think about for a while rather than reply immediately. One of the reasons why I put this on a public forum is that when I was starting out, there was precious little in the way of reference material, and this way it's all available for others who want to read about these things.

That pic. of 8-point stitch on that Lateral to Main Lift junction you using for an example, is not going to break on any deep No slider deployments, it stronger than the forces your body can ever take .

No matter what way you do it . Your Lateral webbing coming out to connect to Main Lift to leg-strap area . If doing a BASE container just try to keep that open bottom area of Tray and the Lateral webbing coming out to minimum .
That inside corner area that I pointing to . Is covered by a Lateral Cover, Also the 'splayed' Lat. webbing in the one Pic. in previous Post , It also helps get rid of the Potential Bridal Snag of open area . The Lat. cover that is in PIc. is really simple, and just cut the bottom angle of it, to meet down there to the Container Tray corner area .


Lat.cover.jpg.8c2efc31bf21b3a20d2c73584a3753f4.jpg
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No direct experience with that machine. But I've often thought that a 7 class was a bit overboard for 5 cord. There are probable machines out there that could handle 5 cord. Make sure you check the lift. Base jumping harnesses are not that thick. You might be able to find a smaller machine that would have the lift that you need and could see through with 5 cord. I can't remember the model. But we had this really old singer. That we got out of a guys barn for $100. We just called it the $100 machine. He was using it to repair really heavy horse tack. Harnesses and shit for the horses. He was sewing with a heavy cord. No markings on the spool. Probably a dacron but it was damn near 5 cord. Single needle simple dropfeed. Looked like a miniature version of a 7-33. That was actually a really great machine. I wonder how small of a needle would carry 5 cord? If you didn't go bigger then you had to that would make it easier to punch the needle through on a smaller machine. 

 

Lee

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1 hour ago, RiggerLee said:

No direct experience with that machine. But I've often thought that a 7 class was a bit overboard for 5 cord. There are probable machines out there that could handle 5 cord. Make sure you check the lift. Base jumping harnesses are not that thick. You might be able to find a smaller machine that would have the lift that you need and could see through with 5 cord. I can't remember the model. But we had this really old singer. That we got out of a guys barn for $100. We just called it the $100 machine. He was using it to repair really heavy horse tack. Harnesses and shit for the horses. He was sewing with a heavy cord. No markings on the spool. Probably a dacron but it was damn near 5 cord. Single needle simple dropfeed. Looked like a miniature version of a 7-33. That was actually a really great machine. I wonder how small of a needle would carry 5 cord? If you didn't go bigger then you had to that would make it easier to punch the needle through on a smaller machine. 

 

Lee

Hi Lee,

I've posted numerous times about the Singer 132K6 machine that I used to build harnesses.  The only limitation was the lift of the presser foot.  I used a #27 needle for #5 cord, and it would sew with ease on anything I could get under the presser foot.

SINGER 132k6 Heavy duty leather sewing machine - YouTube

Jerry Baumchen

PS)  Consew makes a version of it but I do not remember their designation for it.

PPS)  The 132K6 machine is a walking foot & the 132K7 is just a drop feed.

132.jpg.aabeade2fb602f9efeaf179357fef978.jpg

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How much do you actually need? If you need rolls you almost have to find some one local. I don't know any one there other then heathcoat. I might just call up a manufacturer. I used to do crw with Red at flight concepts in Atlanta GA. Really nice guy. He would probably roll off a few cells worth of fabric and sell it to me in an envelope or a small box. I hate folded fabric. You know if you could send hi. The drawings in a format that he could early use he would probably cut the whole canopy for you on his computerized table. Custom colors on fabric. You know is straight. I'd pay for that. And that would break down into a box small enough to ship across the water. 

 

Lee

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