AK Front Trunnion Riveting

[ar15barrels]

The cross-sectional area of an AK rivet is no larger than 0.024 inch

Can you dumb this down for me and show me where you come up with 0.024 inch cross section?
The rivet is around 0.155" diameter BEFORE you set it and it gets larger after it's been set.

[Builder]

Can you dumb this down for me and show me where you come up with 0.024 inch cross section?
The rivet is around 0.155" diameter BEFORE you set it and it gets larger after it's been set.

Oops, sorry about skipping across a few math steps.
On the K-Var website, they have 3 types of rivets. 0.155" diameter, chamfer 0.172" diameter, and the rear trunnion rivet of 0.175" diameter.
Since these are diameters and we need area, we use the area of a circle formula of A = pi x r^2.
So let's take the largest diameter rear trunnion as there are only 2 of them (with 4 shear locations).
0.175" diameter divided by 2 to get radius of 0.0875", then square it is 0.00765". Take this r^2 times pi (3.14) and we get and area of 0.024 sq. inches.
Now that we have the shear area of the largest rivet, we multiply it times the yield strength of mild steel rivets (45,000 psi) and we get 1,081 lbs. The rear trunnion rivets should take 4,324 pounds before it shears.
So even if the smaller 0.155" diameter rivets were set to 0.175" diameter, we still have a maximum shear load that we can obtain. Any smaller diameter rivet will simply carry less load before shearing. I didn't calculate the smaller ones.
0.155" diameter divided by 2 gives us a radius of 0.0775". Squaring radius gives us 0.0060" then times pi (3.14) results in 0.0188 sq. inches of area for a 0.155" diameter rivet. Area times shear load gives us 0.0188 sq. inches x 45,000 pounds per sq. inch yield strength results in 848.6 pounds across the rivet to shear it.
And the chamfer rivet falls in between.
Hope this helps,
Builder

[big103]

Excuse my ignorance, I have never built an AK but I'm planning on building one and have watched the AGI video "Building the AK Semi-Auto Rifle". In the video they instruct you to rivet the front trunnion and receiver together by installing the trunnion which already has the barrel installed, into the receiver. They then tell you to cut a slit in the rivet, inset the rivet into the receiver and trunnion hole, with the slit parallel to the barrel. Then you are to hammer on the rivet head which causes the rivet to mushroom on the barrel.

Has anyone riveted their receiver and trunnion using this method? What are your thoughts on using this method?

Yup it can be riveted with the barrel installed seen it done.

[kcstott]

Yup it can be riveted with the barrel installed seen it done.

here's another dip dunk post.

And no, No you can't and expect good results.

Builder

I was not referring to the shear calculations of the rivet but your weld calculations.
I theoretical engineering a plug weld is calculated off of just shear area alone and yield strength of material. When you step up to structural applications a few more variables are taken into consideration. and you are ignoring at least three variables that I can count off the top of my head.

Also your calculations on the rivets disregard two fundamental elements that apply only to a riveted joint.
The slip limit of the joint and the elastic limit of the joint. This is why I mentioned the note about "Not all things mechanical benefit from rigid mount"

It's apples and oranges comparison and like I said before do what you like to your weapons. If you are an accomplished welder go right ahead.

Most guys here looking to build are not that skilled and are looking for help. Telling a novice he can weld his trunnion to his receiver is just a bad idea. The point you completely missed. You were so concerned about expressing that your technique "would" work you never stopped to think whom might use your advice and if they "Should" do it.

Stack all the cards in your favor and sure a welded trunnion will hold and work just fine for many thousands of rounds and many years. The problem is guys build stuff with welders from Harbor Fright, Tig is not the process of choice, and weld prep?? well that leaves a lot to be desired.

Riveting is the single best way to attach the trunnion to the receiver for one very important reason, Nearly anyone can look at a rivet on an AK and see if it's bad or good. Corrections can be made right there and then. Not everyone is capable of making the same decision on a plug weld.

So all that being said

[valley82]

All arguments aside most of us are restoring these rifles to the original condition to the extent possible. At some point during the last few years I got lucky and lost the desire to be right about anything.

This...I fail to see the point of skipping the very simple step of pressing the barrel out, or skipping the rivots altogether and welding up an abortion...at this point I would not bother to build at all, but that is just me...

[big103]

Just a quick count how many say I`m wrong and this can`t be done?

I`ll hold nothing against you. Can say I`m the biggest idiot on the forums. And some days you might be right.

Mods please don`t delete post if they call me biggest moron in the world I asked for it.

[ar15barrels]

Just a quick count how many say I`m wrong and this can`t be done?

I won't say YOU are wrong and that riveting against the barrel can't be done, because it IS done.
I WILL say that riveting against the barrel without removing the barrel from the trunion is the WRONG way to set those rivets.

There's the BEST way to do things, and there are usually many other ways.
Some of the other ways will work and some others won't.

I only like to do things the BEST way, but you can do what you like...

Cheap, Easy and Right.
Pick any two.

[kcstott]

Just a quick count how many say I`m wrong and this can`t be done?

I`ll hold nothing against you. Can say I`m the biggest idiot on the forums. And some days you might be right.

Mods please don`t delete post if they call me biggest moron in the world I asked for it.

I said you can't and expect good results.

[big103]

I won't say YOU are wrong and that riveting against the barrel can't be done, because it IS done.
I WILL say that riveting against the barrel without removing the barrel from the trunion is the WRONG way to set those rivets.

There's the BEST way to do things, and there are usually many other ways.
Some of the other ways will work and some others won't.

I only like to do things the BEST way, but you can do what you like...

Cheap, Easy and Right.
Pick any two.

I said you can't and expect good results.

So you guys are basically saying you get this. It works for a little while.
But

BOOM

[kcstott]

So you guys are basically saying you get this. It works for a little while.
But

BOOM

No it ain't that.

I know there is high demand and extremely low supply right now for 80% help. So people are trying to get their stuff built any way they can. understandable My first build was a screw build and it has since then been converted back to proper rivets.

The thing is once I learned what was going on and developed a high degree of respect for the AK and got that "it's just an AK" out of my vocabulary I wanted to do things properly Not to mention the first build party I went to drop a truck load of crap on me about doing a screw build and told my why it was a bad idea. Then being the toolmaker I am did some research and figured out these boys are correct. Screws and welds do not belong on a AK trunnion mount.

I still owe a huge debt of thanks to our SD county host, Enthusiast, Tajungatoes, 858Casper858, Mr.Lonewolf, Nicoroshi, Apex22, Mad river arms, Ar15 Barrels, and I know I'm leaving people out but if you were at a Build party that I attended Thank you.

[valley82]

No that was probably either an underpowered round or a spiked round that stuck in the barrel and the next rounds pressure had no where to go but back and out. And shooting full auto he did not have time to realize that the previous round did not leave the barrel.

The worst case scenario I can think of is the rivots loosen up and your trunnion and barrel flop around and then fall on the ground.

[Builder]

Thanks to post #34 for pointing out that there are more than one failure mode of rivets and welds. Rivets can FAIL in multiple ways. So can welds.
Rivets fail with: a)shearing the rivet, b)the plate margin fails reducing the load carrying capacity of the joint, c)crushing of the plate and rivet, d)tearing of plate weakened by oversized plate holes. This last one also applies to when wear of a moving rivet causes the holes to enlarge.
These failures can occur as a result of shear, torsion, or eccentric loading (one rivet taking more load than adjacent rivets). Rivets have an advantage over welding because rivets don't need stress relieving for optimum results.

When welds fail, they fail in the weld because of inclusions or porosity, in the HAZ because of brittleness (reduced ductility) that usually requires stress relieving to solve, weld design, over heating of weld (hot crack), poor surface prep, inappropriate base & filler materials, and insufficient penetration or material in weld. These problems can be solved by proper choice of filler rod, proper preparation, joint design & fit-up, preheating & postheating, stress relieving, and proper training.

All these failures must have loads that exceed the yield strength of the material.

A structural rivet is supposed to prevent movement. A structural rivet joint that permits the slightest motion must be considered faulty. In the late 1800's, it was known that rivet joint movement preceded the action of shearing of the rivet shaft. Thus, rivet joint movement eventually leads to failure from friction. Unless the joint is designed for movement as in a hinge application, but then it isn't intended to prevent motion like the trunnion rivets. Relying upon rivets or welds for shock absorption is a poor design. Both are intended to prevent motion.

Both techniques need proper installation to do their structural job.

Just remember that radial riveting is superior to single pressing of a rivet. The bolt cutter rivet press is not as good as a radial compression of the head.

All this discussion is predicated on the "If I was a PSI, how would I get out of here." Thus the pealing of a weld or the popping off (shearing) of a rivet head are not the load path in this discussion. This would be like prying the weld or rivet off the trunnion.

The elasticity of a material is typically below 30%, beyond which the yield strength begins the failure mode. Mismatching elastic coefficients of different materials can lead to premature failure when the lower elastic material loads up first and then yields.

If the people are not that experienced or skillful enough to build an AK all by themselves, then where do they turn to? Us, who have more of both. Is holding back information advantageous to them?

Actually TIG IS the process of choice. MIG, stick, and Ox/Ac are not as controlled and repeatable as TIG. Like almost anything in life, a skill is something that needs to be learned. Good TIG welding is not that difficult to learn. From other welders who have used the HF TIG machines, they may not be so horrible for light duty use. Miller, Lincoln, Robart, and maybe one or two of the imported inverter machines are the better choice for many years of service.

Just because someone did something one way 65 years ago, doesn't mean that we have to keep doing it.
Thanks,
Builder

[bigbob76]

No that was probably either an underpowered round or a spiked round that stuck in the barrel and the next rounds pressure had no where to go but back and out. And shooting full auto he did not have time to realize that the previous round did not leave the barrel.

The worst case scenario I can think of is the rivots loosen up and your trunnion and barrel flop around and then fall on the ground.

My guess was it was a rifle built in one of the little dirt floor shops where they can replicate any firearm appearance wise. Metallurgy, etc. or the laws of physics for that matter do not come into the picture in those shops. But I understand there are shops/factories where they do build real rifles with good materials.

[kcstott]

My guess was it was a rifle built in one of the little dirt floor shops where they can replicate any firearm appearance wise. Metallurgy, etc. or the laws of physics for that matter do not come into the picture in those shops. But I understand there are shops/factories where they do build real rifles with good materials.

Yeah I was thinking at least really bad head space and a kabluey

[kcstott]

Just because someone did something one way 65 years ago, doesn't mean that we have to keep doing it.
Thanks,
Builder

Tell that to Carrol Shelby
Russel Meredith of Northrop Aircraft perfected the process in 1941.[4] Meredith named the process Heliarc because it used a tungsten electrode arc and helium as a shielding gas, but it is often referred to as tungsten inert gas welding (TIG);

the Bridgeport J2 head being introduced in 1953 and the V ram in 1956 has set the standard by which all other machine tools are judged

The AR15 devepoped in 1957 being a lighter design of the AR -10, ArmaLite sold its rights to the AR-10 and AR-15 to Colt in 1959. After a tour by Colt of the Far East, the first sale of AR-15s was made to Malaya on September 30, 1959, with Colt's manufacture of their first 300 AR-15s in December 1959.

So tell me again how something that is 65 years old is out dated???