TCinVA
12-01-2021, 07:54 AM
Thread locking products seem to be a source of significant confusion. Hopefully this little writeup will help clear up confusion on the use of the Loctite product.
As slide mounted dot optics become more common, more people are going to run into problems mounting optics. This usually manifests in fasteners that hold plates or optics coming loose or breaking off. Sometimes materials and manufacturing defects produce this outcome, but user error the most common and the most easily controlled reason why optics mounting fails.
Fasteners -
The first thing to understand is that fasteners work essentially like a spring. When you tighten a fastener down, the fastener itself elongates applying force on the bearing surface around the fastener's head to clamp down on whatever it is being screwed into.
80740
The fasteners we are using on slides usually tighten down into a blind hole drilled and tapped into the slide itself. If a fastener snaps or breaks, extracting it from the blind hole usually requires specialized tools and knowledge to accomplish.
If we stop a moment to think about the implications of fasteners stretching when tightened, and then we think about the consequences of breaking a fastener off in a blind hole, it would make sense to adopt a best practice of replacing fasteners whenever practical to do so.
The materials and manufacture of the fastener will have a lot to say about how many times that fastener can be stretched or how much stretch it can endure without a catastrophic failure...but your typical end user has no way of measuring any of those things. Fasteners that have never been stretched provide the widest margin for error should they be over-torqued, and the bearing surfaces on the unused fastener are going to have the best engagement with the bearing surfaces in the tapped hole.
From a risk mitigation perspective, simply replacing the fasteners whenever practicable to do so would be a solid way of avoiding a broken fastener and lessening the chances of the fastener loosening under use. This would become especially important if you are using an optic like the Trijicon RMR or some of the smaller optics that require removing the optic from the slide to replace the battery.
Fasteners included with optics or firearms are usually being sourced from a big wholesaler like McMaster/Carr, meaning you can also purchase the very same fasteners yourself. You simply need to know the length, the thread pitch, and the shape of the fastener’s head for your use. Often the fasteners used by manufacturers of more budget style optics are of inferior quality, so purchasing your own might actually allow you to get a better-quality fastener that is stronger and more durable.
Loctite -
You might think that the threads cut into fasteners make complete contact with the corresponding threads cut into the nut or the mounting hole they are being screwed into, but that’s not quite the case. One side of the thread is actually forced into that close contact, but the other is not. This allows a gap to form.
80741
If the fastener is installed in a static, dry environment this is not a problem. In our case, however, the fastener will be exposed to some fairly violent vibrations, impact, temperatures, and a humid environment. Remember that our fastener operates essentially like a spring. With a gap between the bearing surfaces, our “spring” can move, allowing the fastener to become loose. The more rapid and forceful the vibrations, the more quickly the fastener will come loose.
Thread locking products made by or similar to the LocTite family of products function by trying to fill these gaps with an anaerobic adhesive. These products are a liquid or a gel in the presence of oxygen. When the fastener is tightened, air is driven out. Without the oxygen standing between the compounds in the adhesive, it borrows ions from the metal in the fastener and the work piece, forming stronger polymer chains. These chains network together eventually filling the gaps with a solid polymer substance that gives the threads of the fastener nowhere to move to. The solidification process is typically referred to as "curing".
80742
Preparation -
Anything that gets between the thread locker product itself and the surface of the metal hinders the ion-borrowing process critical to a proper cure. Dirt, debris, grease, oil, water, corrosion etc will reduce or completely eliminate the ability of the thread locker to form the bonds necessary to solidify. The hole and the fastener both need to be cleaned and degreased with some sort of volatile cleaner that won't leave any residue behind. High concentration isopropyl alcohol can be used for this as it performs the function and evaporates quickly without leaving behind an interfering residue. You want to go with the highest concentration you can get for this purpose because what isn't isopropyl alcohol is water.
Loctite actually makes a cleaner/degreaser product (https://www.amazon.com/ODC-Free-Cleaner-Degreaser-oz-Aerosol/dp/B000WSIYOY/ref=sr_1_1?keywords=B000WSIYOY&qid=1638362021&s=industrial&sr=1-1) that is compatible with their thread locker products in an aerosol form, which can be useful for blowing crud out of the blind holes themselves.
Activator -
The aforementioned ion-borrowing process requires surfaces that readily give up ions to the material. Some materials are more "passive" or "inactive" than others when it comes to handing out ions. Temperature also plays a role in this process. The lower the temperature the longer it takes to achieve a proper cure.
The curing process can be significantly enhanced by use of Loctite's activator (https://www.amazon.com/Loctite-494147-Anaerobic-Activator-Aerosol/dp/B0002KKTSG). The activator helps the cure set up properly on more passive substrates, promotes curing in lower temperatures, but most importantly to many of us it will actually significantly speed up the curing process by several hours. Typical advice given on the use of LocTite is to wait a full 24 hours before using the pistol to allow for a proper cure. That's not bad advice as it gives enough time for the product to cure on even passive substrates at lower temperatures.
Use of the activator, however, can reduce the time for a proper cure down to three hours or less. That might come in handy at a class, a match, or in the field.
Activator isn't strictly necessary, but if you want a little extra insurance it's a pretty good option.
Application -
The vast majority of the fasteners we deal with in mounting optics on slides go into blind holes either to hold the optic itself or an adapter plate on the slide. LocTite's recommendation for application in blind holes is to use a little of the liquid product applied on the fastener and then more applied directly to the blind hole. Air is displaced as the fastener is tightened. As it is displaced, the liquid LocTite is essentially sucked up through the spaces left between the threads of the fastener and the threads in the tapped hole to distribute evenly and fill the aforementioned gaps:
80743
In this video you can see the process in action:
https://youtu.be/3E42wQG3P4M
Keep in mind that the practices shown above are directly from LocTite themselves.
Filling the hole completely will just result in a lot of excess product spilling out of the top that then has to be cleaned up. I will generally fill the hole between 1/3 as shown in the video and 1/2 depending on how precise I can be with the dropper. If you can be more precise than that, by all means. I find it difficult to just hit the bottom third of the female threads in the holes we're working with and the typical applicators. We're often working with very small holes that don't have the capacity for much volume. If you get more in the hole than you want, you can wick some away with the tip of a paper towel.
If you've used enough product there should be at least some excess to clean up. If you aren't seeing at least some of the product come out around the head of the fastener you were probably a little too sparing in your use. Again, remember that what we are trying to accomplish is filling the gaps between the male and female threads with adhesive so our "spring" doesn't have the ability to shift or move when it experiences vibration or impact.
As slide mounted dot optics become more common, more people are going to run into problems mounting optics. This usually manifests in fasteners that hold plates or optics coming loose or breaking off. Sometimes materials and manufacturing defects produce this outcome, but user error the most common and the most easily controlled reason why optics mounting fails.
Fasteners -
The first thing to understand is that fasteners work essentially like a spring. When you tighten a fastener down, the fastener itself elongates applying force on the bearing surface around the fastener's head to clamp down on whatever it is being screwed into.
80740
The fasteners we are using on slides usually tighten down into a blind hole drilled and tapped into the slide itself. If a fastener snaps or breaks, extracting it from the blind hole usually requires specialized tools and knowledge to accomplish.
If we stop a moment to think about the implications of fasteners stretching when tightened, and then we think about the consequences of breaking a fastener off in a blind hole, it would make sense to adopt a best practice of replacing fasteners whenever practical to do so.
The materials and manufacture of the fastener will have a lot to say about how many times that fastener can be stretched or how much stretch it can endure without a catastrophic failure...but your typical end user has no way of measuring any of those things. Fasteners that have never been stretched provide the widest margin for error should they be over-torqued, and the bearing surfaces on the unused fastener are going to have the best engagement with the bearing surfaces in the tapped hole.
From a risk mitigation perspective, simply replacing the fasteners whenever practicable to do so would be a solid way of avoiding a broken fastener and lessening the chances of the fastener loosening under use. This would become especially important if you are using an optic like the Trijicon RMR or some of the smaller optics that require removing the optic from the slide to replace the battery.
Fasteners included with optics or firearms are usually being sourced from a big wholesaler like McMaster/Carr, meaning you can also purchase the very same fasteners yourself. You simply need to know the length, the thread pitch, and the shape of the fastener’s head for your use. Often the fasteners used by manufacturers of more budget style optics are of inferior quality, so purchasing your own might actually allow you to get a better-quality fastener that is stronger and more durable.
Loctite -
You might think that the threads cut into fasteners make complete contact with the corresponding threads cut into the nut or the mounting hole they are being screwed into, but that’s not quite the case. One side of the thread is actually forced into that close contact, but the other is not. This allows a gap to form.
80741
If the fastener is installed in a static, dry environment this is not a problem. In our case, however, the fastener will be exposed to some fairly violent vibrations, impact, temperatures, and a humid environment. Remember that our fastener operates essentially like a spring. With a gap between the bearing surfaces, our “spring” can move, allowing the fastener to become loose. The more rapid and forceful the vibrations, the more quickly the fastener will come loose.
Thread locking products made by or similar to the LocTite family of products function by trying to fill these gaps with an anaerobic adhesive. These products are a liquid or a gel in the presence of oxygen. When the fastener is tightened, air is driven out. Without the oxygen standing between the compounds in the adhesive, it borrows ions from the metal in the fastener and the work piece, forming stronger polymer chains. These chains network together eventually filling the gaps with a solid polymer substance that gives the threads of the fastener nowhere to move to. The solidification process is typically referred to as "curing".
80742
Preparation -
Anything that gets between the thread locker product itself and the surface of the metal hinders the ion-borrowing process critical to a proper cure. Dirt, debris, grease, oil, water, corrosion etc will reduce or completely eliminate the ability of the thread locker to form the bonds necessary to solidify. The hole and the fastener both need to be cleaned and degreased with some sort of volatile cleaner that won't leave any residue behind. High concentration isopropyl alcohol can be used for this as it performs the function and evaporates quickly without leaving behind an interfering residue. You want to go with the highest concentration you can get for this purpose because what isn't isopropyl alcohol is water.
Loctite actually makes a cleaner/degreaser product (https://www.amazon.com/ODC-Free-Cleaner-Degreaser-oz-Aerosol/dp/B000WSIYOY/ref=sr_1_1?keywords=B000WSIYOY&qid=1638362021&s=industrial&sr=1-1) that is compatible with their thread locker products in an aerosol form, which can be useful for blowing crud out of the blind holes themselves.
Activator -
The aforementioned ion-borrowing process requires surfaces that readily give up ions to the material. Some materials are more "passive" or "inactive" than others when it comes to handing out ions. Temperature also plays a role in this process. The lower the temperature the longer it takes to achieve a proper cure.
The curing process can be significantly enhanced by use of Loctite's activator (https://www.amazon.com/Loctite-494147-Anaerobic-Activator-Aerosol/dp/B0002KKTSG). The activator helps the cure set up properly on more passive substrates, promotes curing in lower temperatures, but most importantly to many of us it will actually significantly speed up the curing process by several hours. Typical advice given on the use of LocTite is to wait a full 24 hours before using the pistol to allow for a proper cure. That's not bad advice as it gives enough time for the product to cure on even passive substrates at lower temperatures.
Use of the activator, however, can reduce the time for a proper cure down to three hours or less. That might come in handy at a class, a match, or in the field.
Activator isn't strictly necessary, but if you want a little extra insurance it's a pretty good option.
Application -
The vast majority of the fasteners we deal with in mounting optics on slides go into blind holes either to hold the optic itself or an adapter plate on the slide. LocTite's recommendation for application in blind holes is to use a little of the liquid product applied on the fastener and then more applied directly to the blind hole. Air is displaced as the fastener is tightened. As it is displaced, the liquid LocTite is essentially sucked up through the spaces left between the threads of the fastener and the threads in the tapped hole to distribute evenly and fill the aforementioned gaps:
80743
In this video you can see the process in action:
https://youtu.be/3E42wQG3P4M
Keep in mind that the practices shown above are directly from LocTite themselves.
Filling the hole completely will just result in a lot of excess product spilling out of the top that then has to be cleaned up. I will generally fill the hole between 1/3 as shown in the video and 1/2 depending on how precise I can be with the dropper. If you can be more precise than that, by all means. I find it difficult to just hit the bottom third of the female threads in the holes we're working with and the typical applicators. We're often working with very small holes that don't have the capacity for much volume. If you get more in the hole than you want, you can wick some away with the tip of a paper towel.
If you've used enough product there should be at least some excess to clean up. If you aren't seeing at least some of the product come out around the head of the fastener you were probably a little too sparing in your use. Again, remember that what we are trying to accomplish is filling the gaps between the male and female threads with adhesive so our "spring" doesn't have the ability to shift or move when it experiences vibration or impact.