First off, my apologies to my high school and college physics teachers for a question that I’m pretty sure I should know the question to.

This week I installed a new muzzle break on one of my ARs. While doing so I used one of those cheap NcStar “do it all” AR wrenches to act as a bridge between the muzzle device and a 3/8” drive torque wrench to tighten it down. The thing that I’m struggling to make peace with mentally is does the drive of the torque wrench being ~6” away from the muzzle device mean that I’m not tightening the muzzle device to the 25 ft/lb that I have the torque wrench set to?

One inch or one foot extension, the torque should stay the same. There may be a minor loss, but not enough to make a difference in what you’re application is.

If you add an extension and the line from the center of the torque wrench drive is straight through (no offset) then you are still at a "zero" of any change in moment.

If you have something like a crows foot or offset at a 90 from the beam/handle then you are still at "zero" of any change in moment.

When the offset of any where other then centered on the wrench's drive, then you need to calculate degrees and length of offset.

There are many torque tables that can help you figure the calculations.

https://www.engineersedge.com/.../torque_wrench_1.htm

^^^^^^^^^^^^^
.Yes.

Yes, what happens when using adapters your changing the length of the handle and leverage. And if your adapter is anywhere but straight in line with handle the value changes again. A little math.

https://www.utilityproducts.co...e%20wrench%20setting.

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https://www.protorquetools.com...-to-a-torque-wrench/

I agree with all of the above. But I agree most with Beancooker because I won't require "math exercises" as sigmonkey & Greymann suggested.

Crush washer???

Call out in the US Army Technical Manual 9-1005-319-23&P is for an anti seize, Loctite C5A. Don't use a torque wrench to install a muzzle device with crush washer. The crush washer is engineered to stay at a consistent torque as it is crushed. Just don't go much more than a turn from hand tight. Simply crank the flash hider on until it's timed correctly

The slow kid has officially caught up with the rest of the class. Thanks for the links to the equations. Seeing it in that format made it click in my brain. I’m a few pounds over the maximum recommended torque but nothing broke so it’s going to stay like that.

quote:

Originally posted by Jelly:
Crush washer???

Call out in the US Army Technical Manual 9-1005-319-23&P is for an anti seize, Loctite C5A. Don't use a torque wrench to install a muzzle device with crush washer. The crush washer is engineered to stay at a consistent torque as it is crushed. Just don't go much more than a turn from hand tight. Simply crank the flash hider on until it's timed correctly

Thanks for this, I learned something new amd useful!

quote:

Originally posted by CEShooter:
I’m not tightening the muzzle device to the 25 ft/lb that I have the torque wrench set to?

It partly depends on your torque wrench range. Torque wrenches have accuracy specs, but those are typically good for 20% -> 100% of the range, so you need a torque wrench where 25 lbs/ft is not at the lowest 20% end of the range.

I think what he was originally asking is, does the torsion bar (extension) change the actual number at the fastener.
The answer is no as long as it's a straight extension. The bar/extension may twist slightly if enough torque is applied but once it reaches the elastic limit for that amount of torque, the number on the other end is the same as at the wrench.
When you torque something to a much higher torque, that deflection is the springy feeling you feel.

Simply stated, torque is force x distance.

Changing the distance changes the torque so any extension added to a traditional square drive torque wrench changes the applied torque. We minimize this by positioning the extension at 90 degrees relative to the wrench. But that assumes the length of the extension is much smaller than the length of the lever arm. In most cases this is "close enough" given the measurement error of the torque wrench. In reality, the lever arm length is the hypotenuse of the right angle...

quote:

Originally posted by 220-9er:
I think what he was originally asking is, does the torsion bar (extension) change the actual number at the fastener.
The answer is no as long as it's a straight extension. The bar/extension may twist slightly if enough torque is applied but once it reaches the elastic limit for that amount of torque, the number on the other end is the same as at the wrench.
When you torque something to a much higher torque, that deflection is the springy feeling you feel.

Incorrect. The extension increase the torque applied to the joint. A torque wrench is only accurate when the applied torque is at the square drive.

220-9er I don't read OP as using torsion bar extension. But rather a AR/M16 Armorer's Barrel Wrench type setup. Correct me if I'm wrong here.

He would have to be at 90 deg from the handle on the torque wrench to the Armorer's Wrench for the numbers not to change.

quote:

Originally posted by Jelly:
220-9er I don't read OP as using torsion bar extension. But rather a AR/M16 Armorer's Barrel Wrench type setup. Correct me if I'm wrong here.

He would have to be at 90 deg from the handle on the torque wrench to the Armorer's Wrench for the numbers not to change.

I think some are overthinking this.
Anything that changes the length of the lever arm will change the torque value.
A straight shot down from the center of the square drive to the center of a socket will have no effect on the torque value. If he has a crowsfoot or something else at the bottom end that offsets the centerline of the extension on the fastener, then the torque value at the wrench will be slightly different.
The truth is, probably not enough to matter in the real world.

I think there is some confusion between what an Extension is and an Extension Lever. To be specific an Extension is a something to attach to a ratchet to allow your socket to reach into a deep opening or to provide clearance for the ratchet swing. A Extension Lever is a short lever that is used to offset a ratchet to the side of the centerline where torque is being applied. One very common Extension Lever is a Crows Foot.

With an Extension Lever there are two forces that are applied when using a ratchet or other rotating lever. That is the linear force applied to the free end of the Extension Lever and the other is the torque being applied to the free end of the Extension Lever. In that diagram showing the torque wrench in line with the extension lever and the center line of the applied torque there will be a multiplication effect on the reading from the torque wrench. to do the math requires that you determine the applied linear force at the handle of the torque wrench. Once that linear force is known you then apply that force to the free end of the Extension Lever to determine the torque produced by the Extension Lever.

So here is all this works. Suppose you have a torque wrench 1 foot long and you apply 10 lbs. at the handle. The torque produced is 10 ft.lbs. Now take that 10 lbs of force and apply it to the free end of your 6 inch long Extension Lever. There you get 5 ft.lbs. So in this case you add 10 plus five to get a produced torque of 15 ft.lbs. when the torque wrench is reading 10 ft.lbs.

BTW then there is an angle other than 90 degrees involved then you have to start doing trigonometry and that can get more complex that I want to go into. There is a real easy way to avoid having to do all this math. That is to place the Lever Extension to that it is in line with the direction of the linear force applied to the handle torque wrench. To put it simply place your Extension Lever so that it is 90 degrees to the line of the Torque wrench.

BTW, this exact "problem" was one of the tasks we had assigned in Statics when I was working towards my degree in Mechanical Engineering.

^^^ Good point on extension vs. extension lever. In this context I used extension to mean a typical AR multi-tool with a square drive hole for a torque wrench. I use the Magpul one, but also have the mil spec one.

In manufacturing we usually call the normal kind of inline square drive extension a "drive extension" and we never say "lever extension" just "crowe's foot" when that's what it is, sometimes adding "open end" or "closed end".

Of course, all manner of strange things are fabricated for hard to reach fasteners, including hacked up hand tools that are cut, bent, and welded into whatever is needed. Since these are almost always attached to preset non-adjustable click wrenches without ratchet heads, we get around the problem by setting the torque using an external calibration unit so all the "math" is eliminated and you set the wrench to the applied torque at the fastener.

It is good to see people being serious about using torque wrenches on AR's, and not just "gudentight" everything, but I always remind myself that torque on dry fasteners is 90% friction when we really want axial clamping load. Using lubricants significantly changes the friction and increases load for a given torque. This can be good, but it can lead to stripped threads and other damage especially on aluminum parts. Not using lube when it is required results in lower loads than intended. Liquid Loctite acts as a lube, but pre-applied patches like the awful yellow ones on Magpul stuff increase friction a LOT. I usually put them in a vise and run the screws in and out to break that stuff in to avoid mangling M-lok slots. Key is to always use the specified lube (or not) with the specified torque.

Ideally we would have specs to tighten to a lower threshold torque, then turn a specified number of degrees that get the desired load, because angle has a much better correlation to load. Not sure if it's worth the bother. Standard AR barrel nuts are sorta like this - tighten to torque then index to next cutout.

Anyone curious about this stuff feel free to ask here or privately. I joke around with design guys in product design reviews that "I just tighten the bolts" but there's a ton of technical stuff and very expensive servo controlled tools you need to use when you havbe to do it right every time on things that you really don't want to come apart in operation. And I've flow halfway around the world on short notice to help fix the process when they do...

This message has been edited. Last edited by: Lefty Sig,

I've always been told that an extension changes the torque value as the torque wrench will lose some force because the extension allows some of the force to be pushed over (instead of straight down) instead of rotational to the socket. How much, who knows and depends on the length of the extension.

quote:

Originally posted by CEShooter:
First off, my apologies to my high school and college physics teachers for a question that I’m pretty sure I should know the question to.

You forgot your English teacher.

Good question though. The crow's foot inline with the wrench vs at 90 degrees has always bothered me, so it's good to finally have an understanding of the math behind it.

As far as extensions go, I've always assumed that by going slowly and smoothly any torsional flex of the extension would have a minimal effect on final torque. Of course I'm only torquing lug nuts, not building engines.