hot glue tool MIL 6645

[rapaz 0]

Hi , I want to ask any technical reason about why on the MIL DTL 6645 , specify this about glue guns ?? ....:

3.4.1 Assembly aids.

For Navy and Air Force procurements, hot glues are not authorized as an assembly aid.

any info will be great, Thanks

[kleggo 138]

one reason that I know of.

I bought a 7 cell canopy in 1981, a Bill Gargano (Spirit, 220 ^2 ft 7 cell).

Great canopy for the time.

It came WITH risers.

One first deployment I lost 1/4 of the suspension lines. The front - left riser's top attachment point had just be folded over and hot melt glued down, not sewn.

I missed that fact and so did any quality control at the factory.

 

Form your own opinion about why "For Navy and Air Force procurements, hot glues are not authorized as an assembly aid".

 

 

 

Edited November 23, 2021 by kleggo

[ChrisHoward 8]

I have no clue about the document you listed so total speculation here. But it could possibly be due to incidents/accidents being caused by forgetting to sew a harness after hot gluing. Rare but has happened (even in recent years) but it couldn't happen if it was never glued in the first place. I seem to remember hearing that some military are now also requiring contrasting harness thread for the same reason.

When was that document last revised?

[riggerrob 558]

Other alternatives include basting harness joints with E-Thread or metal staples. I don't like metal staples because they gum up the harness sewing machine and provide sharp ends that nick my fingers.

[gowlerk 1,903]

17 hours ago, rapaz said:

Hi , I want to ask any technical reason about why on the MIL DTL 6645 , specify this about glue guns ?? ....:

3.4.1 Assembly aids.

For Navy and Air Force procurements, hot glues are not authorized as an assembly aid.

any info will be great, Thanks

The obvious thing is that nylon is sensitive to heat damage and glue guns have hot tips. 

[riggerrob 558]

15 hours ago, gowlerk said:

The obvious thing is that nylon is sensitive to heat damage and glue guns have hot tips. 

Funny you should mention that.

I never contemplated touching webbing with a hot glue gun. But you are correct in saying that it could damage webbing as quickly as a hot knife.

Early in my rigging education I was shown how to hold the hot glue gun tip a centimeter (1/2 inch) above the nylon and never thought about doing it any other way. The only time I ever touched nylon webbing with the glue gun, it slowed down and got awkward.

Another good habit learned early without understanding the theory behind it.

Edited November 24, 2021 by riggerrob

[RiggerLee 61]

At one of the pia meetings before the symposium where all of the mil contractors and government purcurment people get together to bitch at each other this was one of the topics of conversation. I'd did indeed come from a joint not being sewn. Not a heat issue. All the contractors were trying to come up with mechanical jigs and clamps to hold every thing straight during sewing. There was a lot of suppressed grousing under all the "please please can I keep my government contract?" Underneath all the ass kissing was the universal sentiment that hot glue was better faster easier and more accurate. There was a faint hope that the speed would pick back up if they could ever get the clamps to work and not slip but that arranging the peaces  and getting them clamped straight even and on the mark was... Challenging.

For small production glue is so much easier and has a proven track record. As a rigger I could get behind the idea of contrasting thread but I don't see it flying estheticly. Also it makes less then perfect sewing blatantly obvious and I don't see manufacturers volunteering to produce unsightly rigs.

Lee

[JerryBaumchen 1,047]

11 hours ago, RiggerLee said:

At one of the pia meetings before the symposium where all of the mil contractors and government purcurment people get together to bitch at each other this was one of the topics of conversation. I'd did indeed come from a joint not being sewn. Not a heat issue. All the contractors were trying to come up with mechanical jigs and clamps to hold every thing straight during sewing. There was a lot of suppressed grousing under all the "please please can I keep my government contract?" Underneath all the ass kissing was the universal sentiment that hot glue was better faster easier and more accurate. There was a faint hope that the speed would pick back up if they could ever get the clamps to work and not slip but that arranging the peaces  and getting them clamped straight even and on the mark was... Challenging.

For small production glue is so much easier and has a proven track record. As a rigger I could get behind the idea of contrasting thread but I don't see it flying estheticly. Also it makes less then perfect sewing blatantly obvious and I don't see manufacturers volunteering to produce unsightly rigs.

Lee

Hi Lee,

Re:  I don't see manufacturers volunteering to produce unsightly rigs.

My having now known of two rigs where the reserve risers were not completely stitched ( one in which all four risers were not stitched ), I think anything to ensure this does not happen again is very important.

I see the contrasting stitching only needed on the reserve risers; and, possibly on the ring-to-harness attachment.  This is covered by the 'mud flap' so is not normally seen.

Here is a photo from the Javelin manual:

Re:  it makes less then perfect sewing blatantly obvious

I would consider that a good thing.

Jerry Baumchen

[RiggerLee 61]

I'm with you 100% but I can sew straight and I don't have much of an esthetic since. Taking the time to change thread is a pain. Manufacturers are obsessed with the appearance of there rigs. And matching the thread hides a host of sins in there less then perfect sewing. They have chosen over and over again that looking cool is far more important to them then functionality. 

 

Lee

[sfzombie13 307]

is looking cool more important than safety?  i don't care much about functionality, they all work, but if one were to be safer than others that is where i would put my money.  they could even solve the problem of changing thread so often by only using white thread for all sewing and not using white for any part of the rig.  it may not stand out a lot against yellow or some other colors, but would against everything at least enough to inspect.

[ChrisHoward 8]

14 hours ago, RiggerLee said:

And matching the thread hides a host of sins in there less then perfect sewing. They have chosen over and over again that looking cool is far more important to them then functionality. 

Manufacturers are now all offering "Contrast Stitching" on containers, binding etc. because people like the look. So they are already doing this to a certain extent and charging a mark up for the extra effort.

As for military requiring contrasting harness stitching. They aren't going to care about aesthetics and manufacturers will do whatever is necessary to maintain those contracts.

[riggerrob 558]

Plenty of military contracts insist on contrasting thread just to make it easier to inspect. As for time lost while changing thread color .... not a problem if you are sewing a hundred risers at a time. It is also a way to use up odd-colored batches of thread/cord only used on a single custom-colored rig.

As for banning hot glue ... the old methods involved E-thread or metal staples to temporarily bast harness webbing together before sewing it with 5-Cord. Metal staples scare me because they often have sharps edges that can damage webbing. 

[RiggerLee 61]

Never did the staple thing. At least not for harnesses. I have used e thread mainly for really heavy stuff to avoid the thickness that glue could add. I was maxing out the lift on my seven class. I actually have a lighter walking foot with more lift that I can baist it with.

 

One advantage of hot glue is actually at the other end of the spectrum. When you're sewing some thing light. I'll use the example of a riser end. Let's say you're sewing a riser of type 8. It's structural. You want it to be strong so sewing it on a harness machine would be the obvious thing to do right? Problem is that even though it's a webbing and very much structural it's still soft and light. Sewing some thing like that on a seven class is very problematic. It's hard to keep from shrinking it and causing point loading. There are a lot of solutions. Sew it some other way, like with a boat load of zigzag. Fold the webbing under again so you have three layers and a little more meat and stiffness to it. That's kind of an extreme example but it holds true in all which patterns. If the stitching is contracting it and can not elongate with the webbing under load then ether the stitches them selves break or they cause point loads in the webbing where the webbing will fail. One thing I will say for glue. It can make the layup stiffer and the the sewing more forgiving. That should not be discounted. Not to mention the fact that it is by far the easiest way to get the layup accurate, even, flat etc and to hold it that way all through the process.

 

I was there in that big general meeting, a fly on the wall, lessening to the biggest players in the industry, like Mills, talk about this. Trying to move to clamps was a huge pain for them. They were optimistic that if they could get a set up that worked that production would pick back up. In theory it would save steps glueing. But most of all they just desperately wanted to keep there contracts.

 

Lee

 

[riggerrob 558]

Dear riggerlee,

Sandy Reid did that 30 years ago.

Circa 1990, he did all the TSO drop tests with a Flexon harness that was only sewn together with E-Thread and a whole bunch of long bar-tacks. Flexon was the first sport harness with hip rings and it passed all the heavy-weight and high-speed tests. Bar-tacks did not become the production standard because Sandy could not find sewing machines durable enough to bar-tack harnesses all day.

Maybe some modern bar-tacker is strong enough to do the job.

[RiggerLee 61]

None of that surprises me. I've thought about similar things my self. Toyed with the possibility of building base harnesses from ultra light weight spectra webbing. Never went forward but it would have to have been sewed with essentially a bunch of bar tacks. Sewing like that has been the norm forever in other industries like the climbing industry. If you look at there harnesses every thing is sewn with a but load of zigzag on some big pattern tracker. 

 

There is no question that this can be done but there are some trade offs. One reason the flexion held together so well was the rings allowing every thing to aline in shear. So with propper design it can be every bit as strong. In fact I think I can make an argument for it better distributing the load across all the fingers of the webbing and better transfering the load through the joint. But... Although it's a smaller needle it's punching that needle through that fabric a lot. It's a known wear issue. Climbing harnesses are considered disposable. They do not and are not expected to last a long time. Think about how old some of our rigs are. That kind of stitching tends to be subject to abrasion. The stitches tend to lie on the surface. Rubbing against rock can abrade them cutting the stitches across large areas of the pattern. I've seen the same thing with roofing harnesses. These things quickly fell apart. A four point sewn lengthwise in a thick loosely woven webbing sinks down into it. It's kind of self protecting. We built a set of roofing harnesses for one of the local skydivers that owned a roofing company. The Gestapo, I'm sorry I ment OSHA, had show up at his site and busted him for not having harnesses for any of his Mexicans. We built skydiver grade harnesses on our seven class. I think there legality may have been questionable. There is probable some kind of certification for fall protection harnesses. They were the the only ones he ever had that held up. All the commercial ones fell apart litterally. They were the only ones his workers would actually use. 

 

I find the trade offs in these questions to be fascinating.

 

Lee

[sfzombie13 307]

i think the gestapo were more concerned about the dates on the harnesses.  commercial harnesses have a date tag that you put the date on when they are first used, then after five years, they get thrown away.  i have two that i have had for almost 20 now that are as strong as the days i used them on the job, one is a miller that is just the harness and is really light, the other is also a miller but has a back support belt built in and i hung my tool bags off of that one when i was a scaffold builder.  i have never seen a miller harness fall apart, or not make it to end of life.  i have seen a couple of saves with them, one was almost 500 feet up.  i still use mine sometimes if i have to work on trees or something.