How to stop a bolt from unthreading completely

[frugalnacho]

I have a guitar with some tuning screws on the bridge that I need to replace (They are called tuning screws, but it's technically just a bolt).  The original factory tuning screws have what looks like some kind of melted metal to the tip of the screw/bolt.  This allows it to adjust all the way down, and all the way up to utilize the full range of the bolt, but prevents it from being completely unthreaded and falling out.

When I replace a few of these bolts I would like to do the same thing to prevent them from unthreading and getting lost, or even just unthreading and falling out when I attempt to back them out to the maximum level.  I tried googling and asking a few knowledgeable people I know, but haven't gotten any good information.  Is there a specific term for this? Is there a specific product I can use for this?  One person told me to just crush the bottom 2 threads after it's in place, but that seems like a bad idea if I ever want to remove it.  I have no plans to ever remove them, but I'd like the option at some point without having to cut them off or replace the bridge.

[APowers]

Two ideas:

1: Two thin-profile nuts threaded on the end and then tightened against each other (maybe with some threadlocker). Presumably this is mostly just a stop to hold against low-torque adjustment, right?

2: Drill a hole across the very end of the bolt (diametrically, not longitudinally), and use some form of cotter pin (or just a small strand of wire, twisted to prevent its falling out).

[GuitarStv]

Blue locktite (NOT THE RED STUFF FOR THE LOVE OF GOD) works very well for this application as long as the screw head isn't too delicate (very small screws may strip out with the added friction from the locktite).  It keeps the screws in place well and prevents them from working loose from vibration.

In general, if the guitar was properly built you should never really be backing out any of those screws to the maximum anyway.


(Blue locktite is also super useful to have kicking around for working on your bike.)

[Metalcat]

Blue locktight is the shit

[HPstache]

Blue Locktite is great, but I don't think it does what the OP is asking for.  It needs to be something that needs to stop the screw from turning out all the way so that it doesn't come out.  Blue Locktite won't do that, but I will prevent it from naturally spinning with vibration, etc.  I would recommend distorting the last few threads as your friends have suggested.  If you ever need to remove it, you can just cut it with a cutoff wheel.

[frugalnacho]

To clarify this is an ibanez guitar with a floating bridge (basically ibanez's version of a floyd rose).  The bridge "floats" because it's not secured to the guitar, it balances the tension of the strings with the springs attached to the back of the bridge.  Once the guitar is in tune and level the there is a locking nut at the top, so the strings are "locked" at both ends to prevent slippage and changing string lengths, and you can go nuts on the tremolo arm and it will just go right back to being level and in tune.  Once everything is locked in place there are fine tuning screws that changed the angle of the saddle slightly to "fine tune" individual strings without having to unlock the nut and retune anything.  Basically once the nut gets locked the guitar is never retuned until the next string change, except for using the fine tuning screws for, well, fine tuning. 

here is a stock image of a similar bridge:



The screws I'm talking about are at the top of the image (I believe they are called thumb screws?).  These screws get used all the time to fine tune the strings, and need to be able to go from fully screwed in, to (almost) fully screwed out, depending on the tuning need of each individual string (and can change from hour to hour).  I'm currently using some metric bolts for my missing screws, but I've finally located some proper replacement screws.  I don't really want to lock the screw, but merely have some type of "stopper" to prevent it from being completely unthreaded and falling out.  It's not the end of the world, and I can deal with it, but it's a minor pain in the ass and I would really like to just prevent them from unthreading in the first place so I can quickly back them all out without worrying about them falling out on me. 

The original factory screws I have look like they have some type of melted metal or something on the last thread, so when you unthread it to that point it just stops and you can't unthread it any further unless you get pliers and crank it. 

[frugalnacho]

Two ideas:

1: Two thin-profile nuts threaded on the end and then tightened against each other (maybe with some threadlocker). Presumably this is mostly just a stop to hold against low-torque adjustment, right?

2: Drill a hole across the very end of the bolt (diametrically, not longitudinally), and use some form of cotter pin (or just a small strand of wire, twisted to prevent its falling out).

I don't think I'll have enough spare room to accommodate 2 nuts on the bolt.  It's only about 10mm long.  Drilling a hole and putting in cotter pins seems like more of a pain in the ass than just dealing with the original problem. 

[APowers]

I see. could you possibly add a small blob of jbweld/epoxy on the end of the screw? Might have to roughen the last thread a bit, just enough to give the epoxy something to grab onto. Or use solder, which sounds like what the mfg did, but that might depend on your soldering skillz.

[frugalnacho]

I see. could you possibly add a small blob of jbweld/epoxy on the end of the screw? Might have to roughen the last thread a bit, just enough to give the epoxy something to grab onto. Or use solder, which sounds like what the mfg did, but that might depend on your soldering skillz.

I'm not sure what the mfg did.  Looks like just a glob of copper colored metal around the bottom thread.  I've seen a lot of different applications of something similar to prevent a bolt from being completely unthreaded.  I assumed there was an actual name for this technique, or an actual product, but I haven't been able to find anything.  I thought maybe I was just ignorant of bolt/mechanical terminology and wanted to consult with the community.   

I should have some JB weld in my basement somewhere, and I have some soldering supplies.  My soldering skills are not excellent, but I can't imagine I you need very precise skills to just put enough onto the bolt to prevent unthreading. 

[GuitarStv]

I don't think there's really a need to do anything with them.

If you get near the end of the adjustment range for a string just unscrew the lock at the nut, screw the thumb screw back to the middle, tighten the string with your regular tuners, and re-attach the nut lock.  Just takes a second or two with a 3mm allen key.  (If you're playing a floyd guitar you should ALWAYS have 3mm and 2.5 mm allen keys with the guitar - many floyded guitars have a key retainer on the back of the headstock for this reason.)

They're not going to fall off with normal guitar usage as long as they're not unthreaded all the way.

[frugalnacho]

I don't think there's really a need to do anything with them.

If you get near the end of the adjustment range for a string just unscrew the lock at the nut, screw the thumb screw back to the middle, tighten the string with your regular tuners, and re-attach the nut lock.  Just takes a second or two with a 3mm allen key.  (If you're playing a floyd guitar you should ALWAYS have 3mm and 2.5 mm allen keys with the guitar - many floyded guitars have a key retainer on the back of the headstock for this reason.)

They're not going to fall off with normal guitar usage as long as they're not unthreaded all the way.

The threads don't move at all on their own - they're not going to fall off.  I would just prefer to have a stopper on them so I can back them out all the way without them coming out.  Some of the replacement bolts I'm using will occasionally fall out when I back them out completely.  It's a minor inconvenience, but If I can permanently fix the problem and make sure they stay in the bridge it would be nice. 

[GuitarStv]

I don't think there's really a need to do anything with them.

If you get near the end of the adjustment range for a string just unscrew the lock at the nut, screw the thumb screw back to the middle, tighten the string with your regular tuners, and re-attach the nut lock.  Just takes a second or two with a 3mm allen key.  (If you're playing a floyd guitar you should ALWAYS have 3mm and 2.5 mm allen keys with the guitar - many floyded guitars have a key retainer on the back of the headstock for this reason.)

They're not going to fall off with normal guitar usage as long as they're not unthreaded all the way.

The threads don't move at all on their own - they're not going to fall off.  I would just prefer to have a stopper on them so I can back them out all the way without them coming out.  Some of the replacement bolts I'm using will occasionally fall out when I back them out completely.  It's a minor inconvenience, but If I can permanently fix the problem and make sure they stay in the bridge it would be nice.

In that case, a little blob of JB weld on the end would be perfect for this application.

[lthenderson]

I should have some JB weld in my basement somewhere, and I have some soldering supplies.  My soldering skills are not excellent, but I can't imagine I you need very precise skills to just put enough onto the bolt to prevent unthreading.

I would not use JB weld on threads if you ever want to remove the thumb screws in the future. Based off your description above, I'm guessing it is just a tin solder blob placed on the threads and the application of a little heat would easily cause the blob to drip off the threads enough for you to unscrew them should you need too.

[sparkytheop]

I'd look for an O ring that fits nice and snug.  You might be able to thread a shoulder washer as well, or get some rubber gasket, cut a small circle, and then cut a little "x", or use a punch, then slip it over the tip of the bolt.

[BudgetSlasher]

A few things come to mind ... if there is clearance. But, but I have no experience with instruments.

1) Standard nut with on the back side with blue loctite
2) Jam nut
3) Nylon locking nut
4) Some sort of adhesive in place of the metal used in the original setup. super glue and epoxy come to mind
5) A soldering iron and a little blob of solder on the end of the screw
or
6) Perhaps you could flatten the last couple threads if the screw with a pair of pliers (might want to test this with a spare machine screw and nut to check that it doesn't damage the nut)