- Location
- Retired in Minneapolis
In another thread the question came up again about why screwlinks and shackles with screws are allowed but not screw gate biners. I'm going to share some of what I gleaned over the years from reading about this topic. Don't expect that I'm going to go out and do the research to corroborate what I'm sharing. That would turn into too big a project.
First, I'll share some mechanical portions. The difference between the threads on biners or links. Then, how we as workers are affected by the mechanics.
There's going to be disagreements, no problem. Keep the discussion polite though. If someone wants to go and research and share enlightening links I'd appreciate the input.
In the mechanical and machining world there are standards for how tight threads are cut. In highly accurate mechanisms like watches, etc. the screw and nut need to have close tolerances. If not, they'll slop and move around and not work as one unit. Then, in other applications the two can, and need to, have larger tolerances. Think of an adjuster in a dirty environment like the mechanisms on a tracked vehicle that spends its life working in a rock quarry. If the threaded adjusters weren't sealed every little bit of dirt would jam the threads. By leaving gaps between the nut/bolt certain sized chunks can still go between and not jam the mechanisms. I can't recall what this engineering standard is called right now.
Now, take hold of a screw gate biner and a link. Run the nut/sleeve of each onto the threads a turn or two. Then, wiggle the nut/sleeve and feel the slop.
Next, look at how coarse the threads are on biners v. links. Take a look at the cross section of the threads. On the biners you'll see a thread that looks more like a lag screw or the Acme thread you'll find on a woodworking vise's jack screw. With the coarse thread it takes fewer turns to move the nut/link. The threads found on links/shackles are much move V shaped and a LOT finer. It takes many more turns to move the nut/link.
Now, combine the two. Looser threads and fewer turns and you have a biner. Since the threads are loose they're much more likely to get jiggled and open than on a link/nut. The fine threads have a lot more friction because there is more metal to metal contact which reduces the chance of jiggling open.
In some applications I don't wrench tighten or thread lock screw links. In my experiences, and I'm not necessarily advocating this practice, over the past 30+ years of using links is that very few have even opened a tiny bit. If you look at the sleeve on a link you'll find that it has six 'flats' just like most machine nuts. I count turns or portions in 'flats'. Over the years the most I've ever had a link open is 3-4 flats when hand tightened. Compare that to how many full turns it takes to completely open a screw link. Then, look at how open the link would need to be to have a rope slip out of the link. For me, personally, I'm comfortable with hand tightening my screwlinks for most, not all, uses. When the time comes to wrench tighten a screwlink the manufacturers recommend snugging up the link with your hand then using a wrench to snug it one flat. It doesn't take much. If you turn it more the whole shape of the link is deformed and the threads get bent. This can ruin a link and it can also lock the threads together. Remember, threads are no more than circular wedges. We all know how much work a felling wedge can do to tip over a tree.
Pins in shackles are much the same. Some have coarse threads like on rigging shackles some are fine like on harnesses. Shackles and links that are more permanent installs like on my harness will be secured somehow. The bridge shackles on my TreeFlex have an insert that locks the pin. Some shackles come with NyLock jam nuts. If the shackle bow is threaded and a NyLock is used you are using the equivalent of three nuts since the NyLock jams the threads. Be sure to know how many times a NyLock can be reused. In some applications they're single use. In the other thread I read that someone had been told not to use thread locking [LockTite, etc.] for life support. I'd want to see that in writing from a manufacturer before I believe it. After having done lots of repairs over the years, and worked in a machine assembly shop in college along with having friends who are millwrights I have a LOT of faith in threalocking glues. More than in wrenches and jam nuts. But...that's just me.
Now...how about screwgate biners for arbos? Sure, they're accepted in other rope activities. But...we're arbos. Our work environment is much different and dynamic that other rope climbing. The chance of a climber not screwing a gate securely enough to eliminate jiggling open is too high. Not counting just plain forgetting to screw it at all.
Now...don't go off-topic here and talk about auto-lockers. If you're still reading you can start another thread of your own.
First, I'll share some mechanical portions. The difference between the threads on biners or links. Then, how we as workers are affected by the mechanics.
There's going to be disagreements, no problem. Keep the discussion polite though. If someone wants to go and research and share enlightening links I'd appreciate the input.
In the mechanical and machining world there are standards for how tight threads are cut. In highly accurate mechanisms like watches, etc. the screw and nut need to have close tolerances. If not, they'll slop and move around and not work as one unit. Then, in other applications the two can, and need to, have larger tolerances. Think of an adjuster in a dirty environment like the mechanisms on a tracked vehicle that spends its life working in a rock quarry. If the threaded adjusters weren't sealed every little bit of dirt would jam the threads. By leaving gaps between the nut/bolt certain sized chunks can still go between and not jam the mechanisms. I can't recall what this engineering standard is called right now.
Now, take hold of a screw gate biner and a link. Run the nut/sleeve of each onto the threads a turn or two. Then, wiggle the nut/sleeve and feel the slop.
Next, look at how coarse the threads are on biners v. links. Take a look at the cross section of the threads. On the biners you'll see a thread that looks more like a lag screw or the Acme thread you'll find on a woodworking vise's jack screw. With the coarse thread it takes fewer turns to move the nut/link. The threads found on links/shackles are much move V shaped and a LOT finer. It takes many more turns to move the nut/link.
Now, combine the two. Looser threads and fewer turns and you have a biner. Since the threads are loose they're much more likely to get jiggled and open than on a link/nut. The fine threads have a lot more friction because there is more metal to metal contact which reduces the chance of jiggling open.
In some applications I don't wrench tighten or thread lock screw links. In my experiences, and I'm not necessarily advocating this practice, over the past 30+ years of using links is that very few have even opened a tiny bit. If you look at the sleeve on a link you'll find that it has six 'flats' just like most machine nuts. I count turns or portions in 'flats'. Over the years the most I've ever had a link open is 3-4 flats when hand tightened. Compare that to how many full turns it takes to completely open a screw link. Then, look at how open the link would need to be to have a rope slip out of the link. For me, personally, I'm comfortable with hand tightening my screwlinks for most, not all, uses. When the time comes to wrench tighten a screwlink the manufacturers recommend snugging up the link with your hand then using a wrench to snug it one flat. It doesn't take much. If you turn it more the whole shape of the link is deformed and the threads get bent. This can ruin a link and it can also lock the threads together. Remember, threads are no more than circular wedges. We all know how much work a felling wedge can do to tip over a tree.
Pins in shackles are much the same. Some have coarse threads like on rigging shackles some are fine like on harnesses. Shackles and links that are more permanent installs like on my harness will be secured somehow. The bridge shackles on my TreeFlex have an insert that locks the pin. Some shackles come with NyLock jam nuts. If the shackle bow is threaded and a NyLock is used you are using the equivalent of three nuts since the NyLock jams the threads. Be sure to know how many times a NyLock can be reused. In some applications they're single use. In the other thread I read that someone had been told not to use thread locking [LockTite, etc.] for life support. I'd want to see that in writing from a manufacturer before I believe it. After having done lots of repairs over the years, and worked in a machine assembly shop in college along with having friends who are millwrights I have a LOT of faith in threalocking glues. More than in wrenches and jam nuts. But...that's just me.
Now...how about screwgate biners for arbos? Sure, they're accepted in other rope activities. But...we're arbos. Our work environment is much different and dynamic that other rope climbing. The chance of a climber not screwing a gate securely enough to eliminate jiggling open is too high. Not counting just plain forgetting to screw it at all.
Now...don't go off-topic here and talk about auto-lockers. If you're still reading you can start another thread of your own.
