Words like leverage, pressure, friction, spring loading come to mind at the moment. Are there any machinists out there trying out this idea, and can it be optimised?

Ivan. ( PS, Maybe this should be considered elsewhere, as I think Phil would agree it is off-topic.)

2. I think it would help to have an understanding of how bolts work. The bolt and nut are squeezing something between them. Engaging the nut and turning the bolt, the thread strecthes the bolt like a spring. The more you turn, the more you stretch, until you reach the yield strength of the bolt. Then it either permanently deforms (threads bend), or the bolt breaks.

The bolt is secured by the friction between the bolt and nut threads. That friction is a material property, and is effected by the materials used for each, and also whether lubricant is used. Yes, sometimes you want to use lubricant in your bolts. “But that reduces the locking friction!” That’s a drawback, but different designs have different needs.

So what happens if you double spiral your threads, so you could install it either left or right handed? You make your bolt useless. The whole grip of the bolt is accomplished by riding the threads against each other. Yes, you typically only engage about 3 or 4 threads between the bolt and nut, but you need to engage those whole threads. The gaps in the diamond teeth threads mean you have less surface area in contact, which means less friction. Oops. There is also the possibility of galling the metal, meaning the metal deforms and sticks together. Now your bolt may not come apart – ever. Makes it hard to replace.

Thread shape isn’t that variable. Some bolts have big threads, some smaller. That makes more threads per inch, but takes more turns to install. As for the thread profile, you have to be able to machine it with a precision cut, you don’t want too sharp of corners in the bottoms of the threads because those cause stress concentrations that can make the bolt break early. And you want to be able to cut the spiral inside and outside of holes. The beveled spiral cut is pretty optimized.

The key is to use permanent fasteners where possible (i.e. rivets, welding, making from one piece of metal, etc). Where you must use bolts, use secondary locking features. That means lockwire, or pins, or locking nuts and locking plates, or adhesives – any number of methods. Also, soft stow. If you don’t have to hard mount to the walls, pack in foam all the way around to dampen the vibrations.

3. I still can’t figure out how you can tighten the bolt to the nut while pulling the bolt away from the nut. First you have to get the bolt through the hole in the objects you’re bolting. Then you have to engage the nut. The nut has to go on after the bolt goes through the hole. How does the nut get onto the bolt if not threaded on from the end? Then you have to stretch the bolt to apply preload to the objects being bolted together. How do you stretch the bolt by pulling it away from the nut, and have the bolt squeeze in on the bolted objects? You are increasing the distance between the bolt head and nut and trying to squeeze the items in that zone. That does not make sense.

First, I cannot see a problem in having a double (helical) screw thread. It would leave diamond-shaped ‘hills’ lined up on the bolt shaft, and also the hole inside the nut. But why? So there would be a choice of which nut to use, depending on the specific requirement. One locking strategy could be to use a spiral wire or spring to insert in the other spiral groove or thread space to lock it in. Another is to manipulate the thread design and shapes and angles that would offer the highest resistance to movement, however caused. That has probably been a requirement for a century or more though, but it has to be re-examined for every new material and every new age , and application.

Then a tool is needed to apply the nut etc, we are talking about a very specific tool, designed to be used specifically for these connectors.

As for the second question, it relates to these tools. It would require some sort of device to pull against the direction of the travel of the nut. Magnetic- probably not, but using spring pressure, relieving a certain resistance built into the nut thread, or even the bolt or both. I know we are talking about small objects here, but compared to nanotubes, this is rocket sized, if not rocket science.

I would like to see what others could make of these maybe impossible ideas, someone may solve the problems, as they usually do. I too wonder why it seems an advantage to have the twin helical threads, just an idea looking for an application. (Reminded of the story (myth?) of lasers- a concept that had no immediate use when first demonstrated.) Jeez it is hard trying to convey a concept with words only. I could draw things better, and I may try that for proof of concept on paper. Give me time. Cutting, or moulding those threads may also be problematic.

Ivan.

1. How does one screw have threads both right and left threaded? (I can think of one way, but I want what you had in mind.)

2. How do you reverse the action of the screw? More specifically, you put the bolt through the hole. How do you thread the nut on the end and then tighten away from the direction of travel? This I can’t figure out.

3. Left or right shouldn’t matter. Handedness makes sense when you have a rotation effect – that can drive the threads to back out. But vibration is not handed – straight vibration can cause both to simultaneously unwind. It is the stressing and relaxing of the metal that releases the inherent friction, which allows the bolt to back out. The bolt will automatically back out the correct direction.

What’s not clear from the experiment was whether the bolts and nuts were installed into something, or just threaded together. That will have an influence.

Besides installation torque, there are other things – patched fasteners, locking helicoils, locking nuts, chemical adhesives, lockwire. All depends on the design intent. Yes, rivets and welding can be used in some places.