How are quick links manufactured? 5

[kjoiner]

Hello,

I was sourcing some quick links for an application the other day and out of curiosity started thinking about how these are manufactured. I have not come up with a method so I thought I would ask here.

The requirements for the threads seem to be:

1. Aligned axially so the "gate" (glorified standoff) can move back and forth
2. Timed properly so the gate can thread on and off to close the link while still threaded on the other side

From what I can tell, there may be some swage marks where a die closes around the link to upset a stop shoulder and form threads. That would have to be done before the nut is threaded on. Also, how is the link formed with the nut in place when there is not a lot of room from the nut to the bend radius?

For reference, here is a picture of what I'm referring to:

Any thoughts on how these are made?

Thanks,

Kyle

 

[TheTick]

I have wondered as well. Getting the threads "synchronized" across an air gap seems like quite a feat.

 

[rb1957]

link initially straight with thread, nut slid on, end upset (so nut doesn't fall off), nut slid to stop then nut end bent, then nut slid to the other end and thread end bent ?

another day in paradise, or is paradise one day closer ?

 

[MintJulep]

Overthinking it.

The thread has plenty of axial slop. They are hardly precision.

 

[SwinnyGG]

The thread has plenty of axial slop. They are hardly precision.

Gotta disagree with that. The ones you get for $2 at Home Depot are certainly not very precise.

The rated version (typically called a maillon in the climbing world) are very precise - on rated maillons the nut typically has the same amount of play on the captive side (when the nut is in the open position) as a class II thread. When closed, there is nearly zero play. In climbing world terms a maillon which is hard to close, usually indicating that the loop has been stretched beyond yield and the thread sections are no longer precisely aligned either axially or in distance apart, is immediately discarded. They're used a lot to create leave-in-place anchors because they're capable of handling multi-directional loads (which a carabiner can't do) and are MUCH stronger than a carabiner of equivalent size, as well as having a high level of durability when left outside indefinitely.

Threads on rate maillons are rolled. I suspect they roll both ends simultaneously but I don't know that for sure. Seems to me it would be relatively easy to control thread start locations. After thread rolling, nuts are threaded on, then the links are bent, then the whole assembly is heat treated. Cheap links from Home Depot probably skip the heat treatment part.

 

[MintJulep]

The ones you get for $2 at Home Depot are certainly not very precise.

Well, that's what the picture is.

 

[3DDave]

Piecework and a couple of hand tools and something to pry against. The threads don't need to have precise starts - at worst they are 1/2 pitch from matching after the bend. They do need to be aligned - the bender does that within some acceptable variation.

 

[hydtools]

A sequence of steps: thread one end, bend it, put the nut on, thread the other end, bend it.

Ted

 

[3DDave]

https://www.youtube.com/watch?v=M9pdZHTtEkc

has part of it.

 

[kjoiner]

Hello,

Thanks for the great posts. It does seem there is some hand operations in the threading of the nut onto the link. Based on the posts above and the video Dave attached, I think I see how it's done:

1. Take a straight rod and upset one end
2. Thread both ends of the rod. The "stop" end has a shoulder from the upset operation to give the nut something to bear against when tightened.
3. Bend the "non-stop" end
4. Run the nut onto the "non-stop" end until its face is flush the with rod face
5. Bend the "stop" end
6. Run the nut onto the "stop" end. I noticed they have some type of wheel they press the nut against to spin it quickly.

Kyle

 

[swimfar]

If you could figure out a way to roll the threads after it's bent into shape that would ensure that the threads are all aligned or timed.

 

[kjoiner]

Hi Swimfar,

The issue with rolling the threads after is the nut is always covering the threads on the open side. My thought is the threads are rolled when the rod is straight so they are timed correctly. Then the rod is bent in two stages to allow the nut to be installed before the other side is bent.

 

[3DDave]

The "timing" is based on the spacing between the threads. If the helix of one thread aligns with the helix of the other, regardless of where the thread terminates on either open end, the nut will thread properly.

 

[kjoiner]

3DDave,

That's a good observation. My use of timing is not the correct term since angular orientation of the nut is not important (as it would be on a rifle barrel with iron sights screwed into a receiver) The axial spacing ends up being important either way but with looser tolerance and lots of experience, the manufacturers have it pretty well sorted out.

I am enjoying this thread and glad I posted it. Lots of good conversation and maybe a spark for new ideas in the future.

 

[swimfar]

The issue with rolling the threads after is the nut is always covering the threads on the open side.

Duh, I completely forgot about that part. My guess now is they are threaded separately, and it's just not that critical to have both threads perfectly in sync. There is going to be some amount of play in the threads. And if the nut doesn't align perfectly with the start of the thread the whole assembly doesn't have to flex too much before they are in time. Also, with the very low thread angle you have a very effective wedge that will spread the two sides apart as you turn the nut. Worst-case, you have to expand it by a distance equal to the thread pitch.

 

[dhengr]

Kjoiner:
I’ll bet there is no thread on the blind end of the curved round bar. It is upset and finished to a mating round (partial hemispheric) bearing surface to match with the inner bearing surface on the nut/coupler. The nut is then put onto the straight round bar and that end of the bar is bent into a half circle. The free end, still a straight end of the bar can then be upset and threaded, and then its half circle bend is formed. If both ends were threaded, one would need to be rt. handed and the other left handed. And, if not careful one end could be started while the other was not engaged. This could lead to a condition where one end had fewer threads engaged, a weak condition, and not good.

 

[SwinnyGG]

Both ends are threaded.

Both threads are the same hand (I've never seen one left hand thread but maybe they exist). When you flip a piece of threaded rod upside down, do you turn the nut the opposite direction?

 

[dhengr]

SwinnyGG:
O.K. Then you are sorta unthreading the blind end as you are fully engaging the threads on the open end, until it tightens against that stop enlargement/collar. This is just fine, as long as the blind thread is long enough to stay fully engaged too. In this way, you are not flexing the bent link (round bar) very much/at all, as you tighten the nut/coupler. Right?

 

[SwinnyGG]

You aren't putting any strain at all into the link when the nut is closed- the threads are aligned axially and spaced such that the nut threads evenly onto both threaded sections.