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(I'm familiar with thread "locking" compounds, purple, blue, and red, but that's not what I'm looking for here. They lock once and then upon breaking the joint, do nothing further.)

I'm looking for a way to tighten up a free spinning clean, easily threading bolt in a threaded hole. Basically I want it to behave as if there is a locking fastener like a "nyloc nut" or an "interfering thread nut" etc.

Any thoughts? The best idea I have right now is sugary syrup or something.

EDIT: to clarify with some examples

Example 1: I have a metal pen, with a threaded metal cap that screws on. The cap screws on like butter, very nice and clean threads. The problem is sometimes I find it has unscrewed in my pocket. I would like the threaded connection to always feel like it has a slight interference fit.

Example 2: I have a folding pocketknife with a single small torx screw that adjusts the tension required to fold out the blade. This screw loosens occasionally and then knife doesn't work properly. Common wisdom is to use blue threadlocker and tighten the screw to the perfect torque. However, I'd like to adjust it frequently without disassembling the whole thing and adding more threadlocker.

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Why not just toss the bolt in the garbage and replace it with an actual screw that matches the threads of the nut? I fail to understand what you are trying to accomplish. –  maple_shaft Jul 10 '12 at 13:10
    
A picture, or a better explanation of what you're trying to accomplish might get you better answers. –  Tester101 Jul 10 '12 at 15:23
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Could you thread a nut onto the bolt, drive the bolt into the threaded hole, then tighten the nut against the joint? –  Tester101 Jul 10 '12 at 15:24
    
Ack! Sorry, I seem to have been terribly unclear. The bolt and threaded hole / nut are both working properly and match great. I said "free spinning" but what I meant was closer to "free running"? The parts thread without resistance. –  Brad Jul 10 '12 at 18:09
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9 Answers 9

up vote 4 down vote accepted

Based on the clarifications, I would recommend using a reusable thread-locking liquid.
Here is a link to one I found that may work. I have not used it. Vibra-Tite VC3 Threadmate http://www.vibra-tite.com (I am in no way affiliated with the Vibra-Tite Company)

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Exactly what I was looking for! Who would have thought to search "reusable thread-locker" :) –  Brad Jul 10 '12 at 18:45
    
Let us know how this works, and accept the answer if it does! –  Alex Feinman Jul 12 '12 at 15:01
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You may have a damaged/stripped bolt or threaded hole. Check to see if the threads on the bolt are damaged then you will need to purchase a new bolt. If the threads in the hole are damaged you will need to install a threaded insert enter image description here

or use a tap and die set.

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Sorry for my unclarity - I meant that the hole and bolt are working perfectly, and I'd like them to have some resistance. The makers of Helicoil distinguish between a "free running" and a "thread locking" coil - I have a free running hole and I'd like to make it act like a thread locking hole by adding a glue of some sort. –  Brad Jul 10 '12 at 18:10
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There are some reusable threadlocking liquids. Here is one I found that may work. I have not used it. Vibra-Tite VC3 Threadmate vibra-tite.com (I am in no way affiliated with the Vibra-Tite Company) –  RSMoser Jul 10 '12 at 18:29
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You could try some really really fine sand - something that will create more friction between the threads without seizing up.

Alternatively maybe you could redrill/thread the hole to a slightly larger size?

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This is definitely on the right track. I wonder if it would sand away all your threads sooner or later... –  Brad Jul 10 '12 at 18:22
    
Only I think if you're constantly tightening/loosening the nut in question. –  The Evil Greebo Jul 10 '12 at 18:38
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Try mixing something gritty with something gooey that won't dry out. Heavy-weight grease plus sand might do the trick. Basically you're trying to make threadlocker compound but without the property that it dries out. Try it out on another bolt/nut combo FIRST, to see if it works, before gumming up your target bolt.

You may be overthinking this one, though. I'm guessing the bolt hole is really hard to replace or something?

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Yeah, I'd be using this for bolts where I couldn't use a ny-loc nut. I added some examples like a screwing metal cap on a metal pen, and the bolt that holds a pocketknife together. –  Brad Jul 10 '12 at 18:23
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how about plumber's thread tape? (AKA 'teflon' tape)?

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Interesting. I've used this to smooth up the threads on flashlight caps and it does add a bit of friction. (Which is a little ironic?) –  Brad Jul 10 '12 at 18:16
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Is there room to add a second nut? If so, use a second nut as a "jam nut" to act as a locknut: slightly overtighten the inner one, put on the outer one so that it will allow the inner to move out only to where you want it to end up, then "loosen" the inner one 'til it touches the outer one, then use two wrenches to tighten the outer while loosening the inner. The tension between the two nuts prevents them from moving, but it's easy to reverse the process if you need to make adjustments later.

This page has some images: http://www.boltscience.com/pages/twonuts.htm

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My goal is to be able to adjust the connection repeatedly while maintaining vibration resistance. –  Brad Jul 10 '12 at 18:14
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If the bolt is just slightly slipping, and not really "free spinning" you could look to deform slightly the threads of either the bolt or the hole (or both), so that they don't slip anymore.

I used this successfully to fix a landscape lighting fixture that had a 2-part post where the threading between the sections was stripped. Slightly tapping each part of the threaded connection was enough to transform it from a full circle to an ellipse where the threads didn't slip at all and the exterior junction still appeared normal.

I'd been looking for some epoxy or something to hold the parts together, but this ended up being a much easier fix--especially since both pieces were hollow and easy to deform just enough.

Not sure if it'll help in your case, but it's a suggestion in case it might.

landscape lighting fixture

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I guess free-spinning was entirely the wrong word - how about free-running? Deforming one of the threads seems like a good idea - maybe crush the bolt in a vice or vice-grips. Hmm... –  Brad Jul 10 '12 at 18:21
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I had the same problem with a fountain pen cap, and found this post while searching for a solution. I ended up using Loctite® Threadlocker Blue 242®, by spreading a very thin layer on the threads. It's a "removable" thread locker, and has been working great for me so far.

Just don't use the Loctite® Threadlocker Red 271™, because that creates a permanent bond.

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OP says in the first line of the question that he's aware of these products and that they don't work for him. –  Niall C. Oct 1 '13 at 14:23
    
I was under the impression they glued once and then went brittle -- thanks for the info! I'll keep "a thin layer of Loctite 242" in mind as a future option. –  Brad Jun 30 at 4:38
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If it is something that you are unlikely to need to remove at a later date, or if you are OK having to destroy the bolt/nut to remove it, you can use epoxy to bond the bolt and nut.

Epoxy

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Nah, I would like to adjust it frequently. This is similar to red thread-locker. Maybe even super-red :) –  Brad Jul 10 '12 at 18:15
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