Conflicting torque specs

[12Bravo20]

When it comes to looking up torque values online, you need to look at all of the specs to include what material the parts being assembles are made of. Steel can take a higher torque value than aluminum can.

I had several arguments about the torque value of #12-32 machine screws like what Savage uses for their rimfire rifle action screws. Guys kept quoting the torque value for steel at 60 inch pounds. Aluminum will not take that high of torque without damaging the threads. Savage only recommends 15 inch pounds. And at 60 inch pound, you would crush the stock unless you have an aluminum chassis and pillars installed.

Like I stated in my earlier post, most manufacturers will recommend 18 inch pounds for scope rings and 25 to 30 inch pounds for the mounts (mount to rifle). Most of the different brands of AR one piece scope mounts I have all say to use 28 inch pounds.

 

[entropy]

Do not torque scope rings screws down on any Vortex scope past 18 in/lb. Sticking with the numbers 12Bravo20 mentions above will hold well and not cause damage. Hawke actually recommends 16 in/lb., and I stick to that strictly with them.

 

[Kaldor]

I have plenty of rings and scopes that list at 18 lbs. And for those rings, I just go 18 in lbs. But....
Want to see something crazy?

M-BRACE SCOPE RINGS

americanrifle.odoo.com

I have a couple of sets of these rings. They go 55 in lbs on the scope and rail. Never had an issue.

 

[Gun-Reck]

Earlier this year, I picked up a Vortex Venom 3-15x44 first focal plane scope on sale. Didn't come with a mount and waited a while to pick one up. Ordered a 34mm cantilever mount from Midwest Industries. However the scope says do not torque beyond 18in/lbs. But the mount says torque to 20-25in/lbs.

So do I follow the torque spec from Vortex or do I use the one from Midwest Industries?

Two things tighten screws - Friction and Thread Deflection.

Friction - is variable, it can resist torque and then vibrate loose.
Thread Deflection - is asymptotic, and spring-loads the threads, so that vibration is not an issue.
Grease - at the film level, acts like rubber.

So:
1. Grease the threads and head contact surfaces to mitigate friction.
2. Torque until it resists, and a little more torque doesn't result in any additional rotation.
3. Re-torque after a period, to account for grease displacement to film.

Torque gauge not required or desired.

 

[RetiredUSNChief]

Two things tighten screws - Friction and Thread Deflection.

Friction - is variable, it can resist torque and then vibrate loose.
Thread Deflection - is asymptotic, and spring-loads the threads, so that vibration is not an issue.
Grease - at the film level, acts like rubber.

So:
1. Grease the threads and head contact surfaces to mitigate friction.
2. Torque until it resists, and a little more torque doesn't result in any additional rotation.
3. Re-torque after a period, to account for grease displacement to film.

Torque gauge not required or desired.

Wet torquing should only be done when called for by the specs.

 

[Hunter 08]

Wet torquing should only be done when called for by the specs.

I presume that would also include adding blue loctite to any fastener?

 

[entropy]

Vortex says never use loctite, my boss says always use loctite. Vortex doesn't sign my paychecks.

 

[12Bravo20]

Just don't ever use the red loctite!!!!!!!!!

I usually use a tiny drop of blue loctite on my scope rings. It doesn't take much. I'm a retired machinist/tool and die maker, I would get so aggravated when someone would use red loctite on small screws break things trying to get parts apart. Of course they would expect me to fix their mistakes.

 

[Hunter 08]

Just don't ever use the red permanent loctite!!!!!!!!!

I usually use a tiny drop of blue loctite on my scope rings. It doesn't take much. I'm a retired machinist/tool and die maker, I would get so aggravated when someone would use red loctite on small screws break things trying to get parts apart. Of course they would expect me to fix their mistakes.

Red isn't 100% permanent, it requires heat to break it down to loosen.

 

[Hunter 08]

Vortex says never use loctite, my boss says always use loctite. Vortex doesn't sign my paychecks.

Good to know. Hadn't read the whole thing yet. Just wanted to at least go over some of the stuff.

 

[12Bravo20]

Red isn't 100% permanent, it requires heat to break it down to loosen.

You are correct. But I still won't recommend anyone use it for any screw that is 1/4" diameter or smaller. I've seen too much damage caused by people using red loctite on such small screws.

 

[Walkalong]

I have plenty of rings and scopes that list at 18 lbs. And for those rings, I just go 18 in lbs. But....
Want to see something crazy?

M-BRACE SCOPE RINGS

americanrifle.odoo.com

I have a couple of sets of these rings. They go 55 in lbs on the scope and rail. Never had an issue.

Same here.

 

[Walkalong]

Red isn't 100% permanent, it requires heat to break it down to loosen.

No, it's not "permanent", as heat will make it let loose, but you still don't want it on the screws for your rings etc. A little dab of blue will do just fine.

You are correct. But I still won't recommend anyone use it for any screw that is 1/4" diameter or smaller. I've seen too much damage caused by people using red loctite on such small screws.

Yep.

I usually use a tiny drop of blue loctite on my scope rings

Yep.

 

[Kaldor]

You are correct. But I still won't recommend anyone use it for any screw that is 1/4" diameter or smaller. I've seen too much damage caused by people using red loctite on such small screws.

One thing I have found to help with stubborn screws is to use heat, but not an open flame. I have a 75w soldering iron that will hit about 900 degrees, and I have been able to successfully remove loctited fasteners just by heating the screw up with that by sticking the end in the screw for a bit.

 

[12Bravo20]

One thing I have found to help with stubborn screws is to use heat, but not an open flame. I have a 75w soldering iron that will hit about 900 degrees, and I have been able to successfully remove loctited fasteners just by heating the screw up with that by sticking the end in the screw for a bit.

Good information for those that are unfamiliar with the different types of loctite. It is way too easy to mess the threads up or break screws/bolts off.

And yes I use a good soldering iron for small screws. Now a good propane torch is what's needed when taking 3/8" - 16 UNC or bigger bolts out. Yes I am use to working with metal stamping dies, heavy equipment, and industrial machines.

AS mentioned, a little drop of blue loctite is all one needs and don't over torque scope ring screws or you could damage your scope. 18 inch pounds is the industry standard while some say only 16 inch pounds. And when mounting your rings/scope mount to your rifle, stick with the manufacturer's recommend actions which will be between 25 to 30 inch pounds.

 

[RetiredUSNChief]

I presume that would also include adding blue loctite to any fastener?

Mmmm...maybe, if we're being 100% correct!



If you wet torque something that was supposed to be dry-torqued, then you run the risk of over-torquing the hardware. This is because wet-torquing reduces the friction between the threaded components.

I think the general rule of thumb (unless specified otherwise in a technical reference) is to reduce the torque by 20% if you're going to wet-torque something that's supposed to be dry-torqued.

 

[12Bravo20]

Mmmm...maybe, if we're being 100% correct!



If you wet torque something that was supposed to be dry-torqued, then you run the risk of over-torquing the hardware. This is because wet-torquing reduces the friction between the threaded components.

I think the general rule of thumb (unless specified otherwise in a technical reference) is to reduce the torque by 20% if you're going to wet-torque something that's supposed to be dry-torqued.

I have seen where it is said to reduce the torque value from 20 to 30 percent. Some of that will depend on if you are using some type of lube or anti-seize. using more than just a small drop of thread locker will be the same as using lube or anti-seize. We can dive deep on this subject and get into using formulas and such. But all that is irrelevant to the subject since it only takes a very small drop of thread locker for small machine screws like found on scope rings.

 

[Walkalong]

I agree, I use a touch of blue on cap screws and torque to spec, I don't worry about it. Heck, at 18 inch pounds the accepted level of +/- on your torque wrench is another variable we don't even know.

 

[RetiredUSNChief]

I concur.

As for threadlocker, I'm all about using the minimum strength required. Purple would probably work fine, but I most certainly wouldn't recommend going over blue.

There are a TON of different threadlockers out there, all designed for a variety of materials and uses. Red, blue, and purple are just the common ones most people are familiar with.

And then there's the fact that the vast majority of people outside certain professions who simply don't have their torque wrenches calibrated.

MOST of the work requiring torquing for the average layman probably isn't going to be sensitive enough to bother with such differences as, say, wet or dry torque or running torque.

 

[Gun-Reck]

Wet torquing should only be done when called for by the specs.

Have Never had a greased bolt come loose.

Not on a scope, not on a diesel engine.

Thread deflection - is what holds screw threads.

 

[General Geoff]

Thread deflection - is what holds screw threads.

Never heard of thread deflection, that might be a side effect of bolt stretch (a direct indicator of tensile stress) which is the goal of ideal torque values. Measuring the applied torque of threaded fasteners is just a more convenient way of estimating achieved bolt stretch without the difficult and sometimes impossible procedure of measuring actual overall length of the bolt pre- and post- install.

So:
1. Grease the threads and head contact surfaces to mitigate friction.
2. Torque until it resists, and a little more torque doesn't result in any additional rotation.
3. Re-torque after a period, to account for grease displacement to film.

Torque gauge not required or desired.

Without a torque wrench, step 2 is a shot in the dark in regards to how far you're stretching the fastener. Grease doesn't eliminate friction, it just reduces it, changing the required torque value before elastic deformation by anything from 25 to 50% depending on the type of grease.

And the ideal torque value to achieve elastic deformation (or, in the case of torque-to-yield fasteners, permanent plastic deformation), will change depending on diameter, pitch, and material type of the fastener and what it's being threaded into. See the attached PDF, courtesy of Fastenal.

Thread locker can be used in place of bolt stretch for securing fasteners that are screwed into materials which are not as strong as the fastener itself, such as a small diameter grade 8 steel screw threading into a shallow aluminum part. In these cases, you can easily strip out the threads of the part you're threading into before any actual bolt stretch occurs.

For purposes of scope ring mounting, the weak point may not be the rings themselves but the allowable compression on the scope tube itself, which necessitates limiting the torque value (and resulting tension) applied to the ring screws, again possibly below the point of elastic deformation which would be ideal for holding the screws in place on their own.

 

[RetiredUSNChief]

Have Never had a greased bolt come loose.

Not on a scope, not on a diesel engine.

Thread deflection - is what holds screw threads.

It's not a matter of "coming loose". It's a matter of over torquing.

When you wet torque a fastener that was intended to be dry torqued, the bolt will stretch MORE than it would for a dry torque of the same amount of force. This is because you have less friction, so the fasteners will continue turning longer as you approach the specified torque value on the wrench.

This could cause the fastener being torqued to be damaged if the stretching exceeds its elastic limit.

There are other things to consider as well. You may actually cause damage by exceeding clamping forces, for example. Or the lubricant being used to wet torque may be incompatible with the material being bolted up, leading to corrosion.

Again...the average layman may not have any issues with this for a variety of reasons, most having to do with the fact that they may not be working with equipment where these specifications actually make that much of a difference. I happen to work in a field where these things often do matter and I'm absolutely sure that you would not want me to deviate from torquing procedures without a valid technical justification.

Now...the lug nuts on my car are another matter. But if I were rebuilding an engine, I'd torque exactly the way the source documents specify, because this is an area where it matters quite a bit more.

 

[Walkalong]

Not over torquing is about not damaging threads as much as not coming loose. You can over torque and not have something come loose over time, but we want to be able to take it apart and use it again someday, which means not damaging threads. We may never take it apart, but then again many times we do.

 

[Show Me]

Moral of the story is , tighten the mount to manufacturer spec. Tighten the scope to manufacturer spec. If I'm captian obvious please disregard.

 

[Skylerbone]

Not over torquing is about not damaging threads as much as not coming loose. You can over torque and not have something come loose over time, but we want to be able to take it apart and use it again someday, which means not damaging threads. We may never take it apart, but then again many times we do.

On that note, threads are stretched, as they should be once set to torque value, and they’re meant to be replaced if removed. I doubt most guys are writing the ring manufacturers to request new fasteners if they’ve removed a scope and re-mounted.

This makes an excellent case for using LocTite and a common rail system if you intend to change out optics. Think of it as gluing the screws in place rather than stretching the screw threads.