Some concerns about what a reputable gunsmith said about my rifle

[Mike Islander]

Loctite changes the clamping force applied by the fastener at a given torque valve.

This is because loctite or ANY treatment on the threads changes how the bare metal surfaces slide together, making it easier for them to turn or maybe more difficult for them to turn.

So, 30 in/lb of torque applies some "x" valve of clamping force to hold these 2 parts together. By making the parts slide together easier, that 30 in/lb applies what can be a significant amount more clamping force and that can lead to problems.

There are published torque adjustment factors that you could use if you wanted to be exactly correct. Loctite claims no adjustment is needed when using their products, though.

Doubling the torque applied to any assembly would concern me deeply and I don't think I would allow that person to work on anything that I own

Loctite only changes the torque required to break loose the bolt after it hardens, not the clamping force (which is based on bolt elongation during tightening). The purpose of Loctite is reduce the chance of a bolt working its way loose due to natural reduction in torque during use. Clamping force is based on bolt elongation, which is determined by tightening torque; and during tightening the Loctite has virtually no effect (or small enough to ignore, especially since torque specs get bolt tension correct to about plus/minus 30%).

Once the Loctite sets, torque required to break the bolt threads free increases to the remaining original bolt torque plus the additional torque required to break free the hardened Loctite on the threads (Loctite breakaway torque). This total torque is called "breakloose" torque by Loctite. It not only reduces torque reduction during use, but provides enough additional "reserve" torque to maintain total torque at or above the original torque spec during use, all without any additional torque ever being applied to the bolt during tightening.

That's why you don't need to change the torque during initial tightening and why the clamping force stays to spec, which is what the torque value during tightening is specified to achieve (bolt elongation = preload or clamping force). As long as the bolt doesn't turn, the preload (clamping force) of the bolt stays constant and does its job as a solid spring holding parts together.

 

[Mike Islander]

So, say someone puts a piece of Plastigauge (https://www.plastigaugeusa.com/how-it-works.html) between the scope and the upper and/or lower ring, torques the cap down to spec dry (say, 25 in-lbs, and measures the Plastigauge to determine clearance). And then that process is repeated, except for adding Loctite to the threads, and taking measurements again.

If the compressed (torqued down) measurements of the Plastigauge are the same using dry and Loctite-coated fasteners, there would be no difference in the clearance, and thus no difference in the pressure exerted on the scope tube. Correct? [I am NOT an engineer.]

Assuming the above is correct, does anyone know if this has been done? If not, anyone willing to do it?

No need. Why? Because the k-factor of Loctite is similar to the k-factor of a dry bolt. In other words, the bolt will stretch the same with or without Loctite at a given torque. And that is what you want, a specific stretch. See my post above.

 

[Formidilosus]

People need to read, and reread what @Mike Islander wrote in the last two posts.

The gun industry, forums, gun shops, etc all try to make this way more complicated than it is. Loctite (and other threading locking compounds) have been tested extensively in multiple other fields. The aircraft you fly in uses loctite (and often pinned/wired) bolts. Why? Because when you need a screw to not back out, torque alone isn’t good enough.

The thing that keep screws right is preload (stretch/elongation). You can’t really achieve the requisite stretch on screws that hold scopes.


If you do not want screws to loosen, you degrease, thread lock, and torque. Then you put witness marks on the screw head to o visually ensure that it hasn’t moved.

 

[manitou1]

Keep in mind that wetting screw threads messes up the torque values. Torque values are for DRY THREADS and applying any wetting agent can cause issues.

Secondly, I have seen many, many bolts on bolt rifles "jump" when dry fired with no ill affect.

 

[Jpsmith1]

Loctite only changes the torque required to break loose the bolt after it hardens, not the clamping force (which is based on bolt elongation during tightening). The purpose of Loctite is reduce the chance of a bolt working its way loose due to natural reduction in torque during use. Clamping force is based on bolt elongation, which is determined by tightening torque; and during tightening the Loctite has virtually no effect (or small enough to ignore, especially since torque specs get bolt tension correct to about plus/minus 30%).

Once the Loctite sets, torque required to break the bolt threads free increases to the remaining original bolt torque plus the additional torque required to break free the hardened Loctite on the threads (Loctite breakaway torque). This total torque is called "breakloose" torque by Loctite. It not only reduces torque reduction during use, but provides enough additional "reserve" torque to maintain total torque at or above the original torque spec during use, all without any additional torque ever being applied to the bolt during tightening.

That's why you don't need to change the torque during initial tightening and why the clamping force stays to spec, which is what the torque value during tightening is specified to achieve (bolt elongation = preload or clamping force). As long as the bolt doesn't turn, the preload (clamping force) of the bolt stays constant and does its job as a solid spring holding parts together.

I believe I touched on the fact that loctite claims no need to adjust torque value. I was more speaking to the theory of why some people don't use or recommend loctite and I could have been more clear on that.

I'd also say that more than a couple folks think the only loctite is red loctite and those folks are dangerously ignorant for someone wanting to change an optic down the road.

I use loctite, purple is my choice, when mounting optics and, as per instructions, I make no adjustments to torque values

 

[ssimo]

Loctite changes the clamping force applied by the fastener at a given torque valve.

This is because loctite or ANY treatment on the threads changes how the bare metal surfaces slide together, making it easier for them to turn or maybe more difficult for them to turn.

So, 30 in/lb of torque applies some "x" valve of clamping force to hold these 2 parts together. By making the parts slide together easier, that 30 in/lb applies what can be a significant amount more clamping force and that can lead to problems.

There are published torque adjustment factors that you could use if you wanted to be exactly correct. Loctite claims no adjustment is needed when using their products, though.

Doubling the torque applied to any assembly would concern me deeply and I don't think I would allow that person to work on anything that I own

He is the only one who knows these stocks pretty well to do the best bedding possible and he produces and works on thousands of precision and hunting rifles. His methods can be a bit unhortodox and I will not let him torque the shit out of my bases but i am sure the bedding will be good

 

[redneckbmxer24]

Are you trying to convince us or yourself?

If you want him to bed it, go for it. He’s not the only person that can do it though. If your handiness goes slightly beyond changing light bulbs could do it yourself with some simple stuff and save yourself some money too. Bedding isn’t hard to do.

 

[MtnW]

You lost me when you said 4+ ounces on a 10+ pound rifle makes a large difference to you.

 

[ssimo]

Are you trying to convince us or yourself?

If you want him to bed it, go for it. He’s not the only person that can do it though. If your handiness goes slightly beyond changing light bulbs could do it yourself with some simple stuff and save yourself some money too. Bedding isn’t hard to do.

Why should i convince anyone? Especially zome people i don't even know? On forums this is something that people say pretty often. Doesn't make any sense to me.

Anyway, he is already doing it. Since as you said it is a simple process, it shouldn’t be a problem, even also adapting the atlas aics rem 700 floor plate shouldn’t be that difficult. That said, he was suggested to me directly from the producer of the stock so i am not worried about the bedding and floor plate job!

 

[ssimo]

You lost me when you said 4+ ounces on a 10+ pound rifle makes a large difference to you.

It's ok, i lost you.. what will i do now

Jokes aside, firstly they are more like 7 ounces, not 4! And secondly, even if they were 4, of course they make difference. Not a huge one but they still do, especially because you don't get any practical advantage in return. If weight in a rifle isn't a concern because it's gonna be pretty light (up until around 9 lbs), i prefer steel rings and mount since i don't try to cute weight (i don't want a too light of a rifle, too). If the rifle risk to wait too much i start taking measures to cut the weight as much as I can, until those measures don't give me any major practical drawback, like in this case.
I really don't see why we should talk about this, it's so OT and silly.. i mean, you want 4 ounces more on your rifle? Do whatever you want. For my fitness, my age and my shooting preferences, i like a hunting rifle weighting between 9 and 10 pounds, more or less, so i make my rifles weight like that (more towards 9 pounds-well balanced 9 pounds, for a inside 300 yards rifle, more towards 10, even 10.5 when i want to make longer shots). Shooting a small 50 lbs roes at 500 yards is something for which you have to be as accurate as possible and a little bit of weight definitely helps in this, both for inherent accuracy of the system and for easy of use.

 

[Fowl Play]

Just to jump on the torque/preload discussion because I have quite a bit of experience in this regard. (Have done extensive torque/tension testing on different aerospace joint combinations).

Some interesting takeaways:
* A degreased joint (dry) will have at least +/-30% preload variability for the same applied torque. Depending on materials can be significantly higher. So if you were applying a torque that should theoretically yield 1000lbs of preload, even with test based frictional coefficients (K factors). Actual preload will vary between 700 lbs and 1300lbs.
*Even high end aerospace lubricants like Krytox correctly applied to both the threads AND the underside of the bolt head will only get you +/-15%
* Unless your specified torque value takes the fastener or parent material threads to within 80% of its yield strength. You cannot count torque as preload retention. It will fail a vibration/shock test every single time.
* You really really need to do the prep and correct application Loctite recommends for it to work well (properly degrease, both male/female threads, etc)

There’s more, but it’s actually surprisingly difficult to design a proper joint that can survive multiple shock events without issue.

All this to say. I would definitely use loctite. And apply it correctly. I also would be cautious bumping up torque values from manufacturer recommendations unless you do your own calculations OR have someone knowledgeable to advise you in this regard to what has worked. I definitely do think scope manufacturers could be sandbagging.

 

[Mike Islander]

Keep in mind that wetting screw threads messes up the torque values. Torque values are for DRY THREADS and applying any wetting agent can cause issues.

It's not "wet" or dry that makes the difference in torque; it's the K factor of the bolt under actual conditions. Wet with water is extremely different than wet with oil. Henkel (Loctite) work very hard to tune their locking adhesive preset K factor to be similar to a clean, dry bolt. The "wetness" of the bolt literally is not a factor in the torque equation to produce the desired bolt elongation/preload/clamping force. "Wetness" is not one of the variables in the K factor equation. Only the actual measured K factor matters.

For engineering, intuition is often your enemy. Testing your intuition is literally the only way to know what is real versus what is supposed. As I mentioned before, using torque to achieve bolt preload is accurate to about plus/minus 30%. Slight decrease (or increase) in K factor when using most Loctite products (certainly those we would use) makes no significant difference in bolt elongation, which is why Loctite doesn't recommend changing torque values. It's also why they work so hard to match the K factor of a dry bolt, so you don't need to guess at some reduced torque.

 

[ssimo]

Just to jump on the torque/preload discussion because I have quite a bit of experience in this regard. (Have done extensive torque/tension testing on different aerospace joint combinations).

Some interesting takeaways:
* A degreased joint (dry) will have at least +/-30% preload variability for the same applied torque. Depending on materials can be significantly higher. So if you were applying a torque that should theoretically yield 1000lbs of preload, even with test based frictional coefficients. Actual preload will vary between 700 lbs and 1300lbs.
*Even high end aerospace lubricants like Krytox correctly applied to both the threads AND the underside of the bolt head will only get you +/-15%
* Unless your specified torque value takes the fastener or parent material threads to within 80% of its yield strength. You cannot count torque as preload retention. It will fail a vibration/shock test every single time.
* You really really need to do the prep and correct application Loctite recommends for it to work well (properly degrease, both male/female threads, etc)

There’s more, but it’s actually surprisingly difficult to design a proper joint that can survive multiple shock events without issue.

All this to say. I would definitely use loctite. And apply it correctly. I also would be cautious bumping up torque values from manufacturer recommendations unless you do your own calculations OR have someone knowledgeable to advise you in this regard to what has worked. I definitely do think scope manufacturers could be sandbagging.

Thanks! It's amazing to hear from someone with actual professional competence on this subject. I will do like this for sure. Yeah possibly they are sandbagging but, since I have never had issues torqueing to specs, i will continue to do so.

Just a side note, i qm not sure loctite suggests putting the product on both male and female threads for this application. Videos and TM from them say to just put a drop of 243 on the lower third od the screw and screw it on. Also 243 should be more resilient to oil than its predecessor, the famous 242 blue loctite

 

[ssimo]

It's not "wet" or dry that makes the difference in torque; it's the K factor of the bolt under actual conditions. Wet with water is extremely different than wet with oil. Henkel (Loctite) work very hard to tune their locking adhesive preset K factor to be similar to a clean, dry bolt. The "wetness" of the bolt literally is not a factor in the torque equation to produce the desired bolt elongation/preload/clamping force. Only the K factor matters.

For engineering, intuition is often your enemy. Testing your intuition is literally the only way to know what is real versus what is supposed. As I mentioned before, using torque to achieve bolt preload is accurate to about plus/minus 30%. Slight decrease (or increase) in K factor when using most Loctite products (certainly those we would use) makes no significant difference in bolt elongation, which is why Loctite doesn't recommend changing torque values. It's also why they work so hard to match the K factor of a dry bolt, so you don't need to guess at some reduced torque.

Very interesting. I had to write on rockslide to get an answer for this! I checked online in the past and i found mixed opinions

 

[Fowl Play]

Thanks! It's amazing to hear from someone with actual professional competence on this subject. I will do like this for sure. Yeah possibly they are sandbagging but, since I have never had issues torqueing to specs, i will continue to do so.

Just a side note, i qm not sure loctite suggests putting the product on both male and female threads for this application. Videos and TM from them say to just put a drop of 243 on the lower third od the screw and screw it on. Also 243 should be more resilient to oil than its predecessor, the famous 242 blue loctite

I may be mis-remembering if loctite documentation says to do it, or if it’s my companies internal documentation. Either way, it should be applied to both male and female threads.

Link to one of the lessons learned on this:

Llis

 

[Mike Islander]

Very interesting. I had to write on rockslide to get an answer for this! I checked online in the past and i found mixed opinions

There are tons of opinions that make sense, but are wrong in the real world. Certainly some Loctite products change K factor significantly. We use some for motor housings, etc. But for bolts, and for the products most people use, the K factor matches closely enough that Henkel doesn't recommend changing torque to achieve proper bolt preload.

I would not be surprised if some divisions of Loctite recommend reduced torque for specific formulas, depending on the engineer in charge. But for most uses and most common Loctite types that we shooters use, no need to change torque.

 

[Fowl Play]

There are tons of opinions that make sense, but are wrong in the real world. Certainly some Loctite products change K factor significantly. We use some for motor housings, etc. But for bolts, and for the products most people use, the K factor matches closely enough that Henkel doesn't recommend changing torque to achieve proper bolt preload.

I would not be surprised if some divisions of Loctite recommend reduced torque for specific formulas, depending on the engineer in charge. But for most uses and most common Loctite types that we shooters use, no need to change torque.

Loctite definitely changes the K factor, but also reduces the preload uncertainty as compared to a dry joint. So it can turn out to be a wash.

 

[fwafwow]

There are tons of opinions that make sense, but are wrong in the real world. Certainly some Loctite products change K factor significantly. We use some for motor housings, etc. But for bolts, and for the products most people use, the K factor matches closely enough that Henkel doesn't recommend changing torque to achieve proper bolt preload.

I would not be surprised if some divisions of Loctite recommend reduced torque for specific formulas, depending on the engineer in charge. But for most uses and most common Loctite types that we shooters use, no need to change torque.

I know others have recommended specific Loctites for mounting, but I’d love to know what you and @Fowl Play use. (Apologies if either of you have given that specificity above.)

 

[Mike Islander]

I may be mis-remembering if loctite documentation says to do it, or if it’s my companies internal documentation. Either way, it should be applied to both male and female threads.

Link to one of the lessons learned on this:

Llis

Henkel's recommended practice depends on the configuration. Blind shallow hole, Loctite in the hole only. Through bolts, Loctite on the bolt tip only. Etc., etc. Download some of the many guides from Henkel if you want to really follow their advice. Certainly NASA put some thought into that article, so it probably works as well as, or better than, Henkel's recommendation for those applications.

Whatever you do, if you get Loctite on the threads, it will work "plenty good enough" for most applications.

 

[Mike Islander]

I know others have recommended specific Loctites for mounting, but I’d love to know what you and @Fowl Play use. (Apologies if either of you have given that specificity above.)

I use 222 or 243, whatever is handy (I have a bunch of bottles scattered around m,y 12,000 SF warehouse). As with so many things, either is "plenty good enough".