Does Loctite alter torque on scope rings

[JohnDough]

John, I mount an awful lot of scopes and haven't crushed a tube in at least 20 years. I figure if I can chamber a barrel and true up an action....mounting a scope should be within my capabilities.....but explaining it apparently isn't.

I love the internet.

I don't personally know anyone who HAS crushed a scope tube.

 

[MallardSX2]

Been using a fat wrench for years.

Blue loktite on the base threads and dry scope cap bolt threads.

I use the manufacturers recommended ring torque value and manufacturers base torque value and roll with that.

Never had an issue. Ever. And I hunt my ass off….and I’m pretty hard on things.

I don’t put nail polish on my ring cap bolts either…too ocd for that. Lol

 

[Sundodger]

I've seen loctite modify tension/compression/stretch, and I've seen it not. I think substrate materials are also a factor here.

I believe you. That's why a formal study is supposed to be done, if any of the affects are critical.

Information from some adhesive manufacturers can be misleading. Loctite may still advertise that their locker doesn't affect "torque" but their technical papers stated that a study should be done with and without locker to ensure proper joint connection.

Most of this is unlikely to matter for hunters and shooters. However, as a group, I would just prefer that we don't regurgitate bad information with blanket statements.

That's one of the things I enjoyed about bolted joints, it was an interesting combination of art and science. It is no doubt engineering you can model and make predictions on, but slight changes to materials, process, coatings, etc. can lead to drastically different results. Tons of this testing is conducted at OEM's every year, but they don't just go around publishing their IP.

Couple things I will mention that lead many people astray in this domain:

-Don't think of a torque to tension being a 1:1 relationship, as in if you hit X torque you will get Y tension. Think of it like a bell curve. If you hit X torque the tension lies somewhere on this bellcurve. Or better yet, if you don't have fancy production DC tools that's tq delivery is really precise, two compounding bellcurves one for tq and one for tension. Now you can set up all your virtual conditions.

-Friction will mislead you, it is the "noise" in the system. When you get to 75% proof load on a fastener almost all the tq that is being applied to the bolt is going to friction not tension. This means tiny changes in friction have massive impacts on tension, so there are red herrings everywhere. You need large samples sizes and OCD levels of diligence. Tq + angle is an effective option to battling friction if you have the bolt length.

-Mind your D to L ratio. Not enough bolt stretch will cause joint failures. This is one of the reasons we still use rivets, hucks, etc. today.

 

[IdahoBeav]

I stopped using loctite on rings and have never had a screw back out.

 

[Macintosh]

OK, so it's awesome that there are some engineers and highly trained folks in the "room". I really appreciate hearing from folks like that. Problem is that us laypeople dont know what half of what you said means, or dont have the means to put some of it into practice. So far all the talk is interesting (what I understand of it), but as I've asked various scope ring manufacturers this specific question in the past, none of them yet--even those who officially recommend agsint it-- have said using threadlocker would be a problem other than gumming up threads...so far all have said they either think it's fine, recommend FOR it, or that they only reccommend agasint it becasue so many people are idiots and complain that they used threadlocker and now their screws are gummed up but they still want to return the "unused" product, etc.

What I'm reading between the lines on is that you all dont even necessarily agree, or at least have different/various "exceptions" in mind. Is it possible for @Wrench, @JohnDough and @Sundodger to agree on a simple answer for a "best practice" installing scope rings, and if using threadlocker on scope rings is a problem or not, FOR A LAYPERSON using typical tools, ie the supplied allen key or a fatwrench-type torque wrench? Or is this all so complex and variable that it's not even possible to get 3 people to arrive at the same conclusion?

 

[JohnDough]

OK, so it's awesome that there are some engineers and highly trained folks in the "room". I really appreciate hearing from folks like that. Problem is that us laypeople dont know what half of what you said means, or dont have the means to put some of it into practice. So far all the talk is interesting (what I understand of it), but as I've asked various scope ring manufacturers this specific question in the past, none of them yet--even those who officially recommend agsint it-- have said using threadlocker would be a problem other than gumming up threads...so far all have said they either think it's fine, recommend FOR it, or that they only reccommend agasint it becasue so many people are idiots and complain that they used threadlocker and now their screws are gummed up but they still want to return the "unused" product, etc.

What I'm reading between the lines on is that you all dont even necessarily agree, or at least have different/various "exceptions" in mind. Is it possible for @Wrench, @JohnDough and @Sundodger to agree on a simple answer for a "best practice" installing scope rings, and if using threadlocker on scope rings is a problem or not, FOR A LAYPERSON using typical tools, ie the supplied allen key or a fatwrench-type torque wrench? Or is this all so complex and variable that it's not even possible to get 3 people to arrive at the same conclusion?

If you use threadlocker, it should not be an issue. HOWEVER, "just in case", I always recommend people use products with overlap. This means you use a Nightforce scope in Reptilia mount, because the NF scope is to be torqued to 25 in-lb, and the Reptilia mount to 15 in-lb, so even IF the loctite reduces friction and provides more compression at a given torque value, it's not going to exceed the scope manufacturer's recommendation. I prefer Loctite 243, OR just using a light oil. Scope tube compression is similar to a helicoil in that it keeps tension on the threads during vibration, as it's not a solid joint and has far more "movement under tension" threshold than just bolt stretch would allow, especially with this size fastener.

*I am not an engineer, but I did go very deep down this rabbit hole with people at Geissele, nightforce, Vortex (the only company against thread locker I've spoken to, and even publishing reduced tq values IF it is used in their manuals), Hakan Spuhr, KAC, and others.

 

[Sundodger]

To answer your question, bolted joints are far messier than they would appear on the surface.

Couple of things that might help:
-In general among engineers in the industry, thread locker is viewed in two ways for "hard joints"; as belt and suspenders if you are an optimist, or a band aid on a broken elbow if you are an pessimist.
-In reality there is not really such thing as a "hard joint", joint stiffness it's a spectrum, but it is a nice and useful bucket.
-There are an infinite number of duty cycles a joint can see in service.
-Laymen and engineers have different definitions of a failed joint.
-NASA fastener design manual is a good read for all

https://ntrs.nasa.gov/api/citations/19900009424/downloads/19900009424.pdf

If you have a joint that is considered "hard". Lets say a pic rail to an rifle action. Lets say you get all screws perfectly up to 80% proof load, there is negligible joint relaxation, and that's X amount of pounds of clamping force per screw. If the loads in service (shooting, bouncing around in the truck, etc.) are able to meet or exceed the residual tensile loading in any one of those screws most engineers consider that a failed joint even though it hasn't come apart yet. Why? Because with zero tensile load that fastener can back out, or fatigue (often both). Basically the joint is a ticking time bomb, it will fail if it stays in service, and while threadlocker can help one failure mode here (unscrewing), it doesn't do anything for the other. So either way the joint needs to be more robust (more fasteners, longer length fasteners, etc.)

If you want to get a bunch of fastener engineers arguing with each other, start bringing up load cycles, especially marginal or extreme ones when you are limited to what changes to the joint you can do. If you have the minimum acceptable joint that is robust against 99% duty cycles and the 1% the fastener tensile load is only exceeded occasionally, This is where they often will agree (disgruntled) to using Loctite.

Where this gets messy is where I suspect we find ourselves with ring half's. I have no data but I suspect ring half's are on the soft side of the hard joint spectrum. While they tend to have very fine threads and small diameters (helpful), their length is often not very long and there is not a ton of them (not helpful), combine that is what I bet is a rather "soft" aluminum tube in the middle and you have a tricky problem.

Where it gets interesting is bringing in duty cycle. Lets say the only time the tensile load is exceeded of those fasteners is 10% of the time you shoot. Lets say you plan to shoot this rifle for 1000 or 2000 shots before it gets another makeover. You might convince fastener engineers that thread locker is an acceptable mitigation to this poorly designed joint because 100-200 discreet times where tensile load is exceeded can be lived with if the fastener doesn't back out. High cycle failure bolt failure takes more.

All this to say: I laid out of bunch of conjecture up above, take that for what it is, but I suspect most rings are marginal joints, so pick the most robust you can, and do what works. If you do choose to use threadlocker it is paramount to clean every out perfectly if you reuse. Solvent and lots of thread chasing with threadchasers not taps/dies. Friction is the enemy, so before reassembly the bolt/threads needs to be running like butter.

 

[Sundodger]

Is it possible for @Wrench, @JohnDough and @Sundodger to agree on a simple answer for a "best practice" installing scope rings, and if using threadlocker on scope rings is a problem or not, FOR A LAYPERSON using typical tools, ie the supplied allen key or a fatwrench-type torque wrench? Or is this all so complex and variable that it's not even possible to get 3 people to arrive at the same conclusion?

Without data, it's impossible to know. Follow the rules of thumb on all bolted joints and we all have to do the best we can.

The testing would cost a fortune and wouldn't always translate between other rings. I wonder if they even make load cells small enough for 6 or 8 screw sizes...