Loctite?

Over the last 30 years or so, I have had a lot of different mechanical engineers that I have helped. I am an electrical engineer, and we don't get super bright MEs in electronics, because there are no moving parts, but we get a lot of MEs and we deal with shock and vibration.

The big problems with vibration are falling apart and breaking apart.
At a couple of companies, I will dig this book out of the ME's book shelf and explain it to them:
http://www.amazon.com/Vibration-Analysis-Electronic-Equipment-Steinberg/dp/047137685X

There are lots of applications with high vibration that will not shake loose, and there are lots of applications that will.

When I take a Rem700 barrel off, and find all that goop that the Remington factory left there, I know my calculations say it could shake loose, and they must have had a problem, but darned if I have ever been able to get a Rem700 barrel to shake loose. Vaughn offers a design change to fix this in the Rem700:
http://www.amazon.com/Rifle-Accuracy-Facts-Harold-Vaughn/dp/1931220077

Guns have lots of screws and pins.
The only thing that I have seen again and again and again that came loose are the screws that attach the scope mount to the receiver.

An indicator is two holes touching on the target, followed by two holes touching way over there on the target.

I am not sure why those screws are coming loose.

I have calculated how much torque that scope mount screws should have.
I have tested the yield point of similar steel that is not part of the gun, and my calculations are right on for the various lubricants; 1) clean and dry, 2) oil or grease, and 3) wax.
 
I like many others here am a mechanical engineer. My opinion is that loctite has many good applications in guns.

I generally use low strength. I use thread locker for threads and sleeve retainer type for dovetails, etc.

This said, be sure to prep your surfaces with some light sanding and cleaning with alcohol.

When you apply it, you still need to keep bolts in there elastic range and have parts which fit together.

Loctite's place in design is when design, mfg and use came close to design specs, but something just missed. Instead of redesigning, add some loctite. It is a good designer band aid.
 
My take:I generally put something on threads so its not dry,unlubricated steel on steel.(unless the instructions say so)

These days,I usually put never-seize on barrel threads,but,accepting I will have created a monster if I want to take it apart,I have locktighted some barrels .I am careful with my thread forms and fit to minimal clearances on barrels I thread,etc.I generally true all faces,too.I torqiue a barrel tight enough it wont unscrew,but I do not get crazy about it.Many benchresters use minimal torque on their barrels.

My theory,I wanted to fill in all the clearance and make it a dead joint.Agreed,with fresh,precision threads its probably not necessary,but on a 80 or 100 year old milsurp set of threads,they won't be perfect.

I think that is why Rem loc-tites the bbls in.Its to take out any flex room in the joint...Its not about the barrel unscrewing.

On screws,no need to make more trouble than necessary,many screws don't need it,but on scope mounting,I'll put a touch of sleeve retainer between the base and the receiver as a bedding compound. There are few mechanical fits that are perfect.I use blue on the base screws.

Scope base screws are small for the job they do.They do not engage a lot of depth of thread length.There must be some thread clearance.You hang a big heavy scope on those screws and shock them with recoil,I think of loosening a fence post by working it back and forth.
That is also hard on the female threads in the receiver.So,for me,the loctite is not so much about the screw rotating to unscrew,it stabilizes the joint,removes wiggle room.

Oh,if I ever do need to pull one of those barrels back out,I'm thinking a soak in a pan of hot peanut oil should get it up to temp ,

To the original question,There are few applications for loc-tite on an AR.

Yes,there are marginally designed aftermarket parts,but as the OP pointed out,there are alternate parts with better designs.
 
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I use a thin coat of grease on the receiver threads when torquing an AR barrel nut, the correct torque spec for which is from 36 lbs/ft to 80 lbs/ft. I usually torque to around 50 lbs/ft.

I don't use Loctite on scope rings; I use Torx head scope ring screws, and, per Leupold, use a tiny drop of oil before tightening up the screws.
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Here is a guy doing it right. You cant properly torque a screw/bolt without lubrication. The torque stretches the screw and put proper tension on the head to keap it from slipping and thus loosening. Without lube your torque settings are incorrect because your torquing against the friction of the threads -vs- the stretch of the screw/bolt.
There are extreme cases for non hardening locktite. IE: the engineer designed the part incorrectly or there simply wasnt room for the proper type/size of screw/bolt. When most people are using loctite I use never seize. If i want to sell a new part I use loctite so the customer cant tale it apart.
 
The torque stretches the screw and put proper tension on the head to keap it from slipping and thus loosening.
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And there are probably far more applications that cannot tolerate locking torque than ones that can.

There are also applications that using locking torque is simply inadequate for the environment.
 
The only place I use Loctite (blue) on weapons are scope mounts, scope rings, and action screws torqued to the proper values.
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And the rear sight elevation screw of the Beretta NEOS. :rolleyes:
 
For scope base screws I lubricate, torque to spec, loosen, torque to spec again, remove screws, degrease, blue Loctite and finally torque to spec. Best of both worlds.
 
Threads don't lock that way, anyhow. There are many clearance variations between the male and female minor/major diameters of the fastener and the threaded hole. The thin leading taper edge of the male thread contacts only a portion of the insert thread wall. That leaves the head of the fastener and the spacer or cap washer holding most of the torque anyway. Then, here comes your Loctite...

:eek:

-7-
 
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