AK Front Trunnion Riveting

[nothinghere2c]

while it may not be the correct way, the ak builder rivets work pretty well with the AGI method. i've built a few AKs that way with thousands of rounds through them and its still solid.

hate away, but its fast and easy.

[ar15barrels]

while it may not be the correct way, the ak builder rivets work pretty well with the AGI method. i've built a few AKs that way with thousands of rounds through them and its still solid.

Fast, Easy & Good.
Sounds like you picked your two.

[Builder]

For a little TIG welding stress calculations, let's look at the loads of each button (rosette) weld.
A 0.25 inch wide by 0.125 inch deep weld has an area of 0.03125 sq. inches.
0.03125 sq. inches times 65,000 psi 4130 yield strength results in each weld capable of holding 2051 pounds.
But if the weld is too hot and the weld's Heat Affected Zone is weaker, say 25,000 psi, then each weld of 0.03125 sq. inches could carry 750 lbs.
With 3 welds on each side of the forward trunnion, these welds can carry between 4,500 pounds to 12,306 pounds.
Is that NOT strong enough?
Thanks,
Builder
Info on welding 4130 at: http://www.netwelding.com/Welding%204130.htm

[kcstott]

For a little TIG welding stress calculations, let's look at the loads of each button (rosette) weld.
A 0.25 inch wide by 0.125 inch deep weld has an area of 0.03125 sq. inches.
0.03125 sq. inches times 65,000 psi 4130 yield strength results in each weld capable of holding 2051 pounds.
But if the weld is too hot and the weld's Heat Affected Zone is weaker, say 25,000 psi, then each weld of 0.03125 sq. inches could carry 750 lbs.
With 3 welds on each side of the forward trunnion, these welds can carry between 4,500 pounds to 12,306 pounds.
Is that NOT strong enough?
Thanks,
Builder
Info on welding 4130 at: http://www.netwelding.com/Welding%204130.htm

You mistake weld strength for superiority in joint construction.
Yes a tig weld is strong but it is too rigid for the application. The riveted joint is a flexible joint allowing the parts to move under stress and return to original position post stress. All I see here is an analyses of the weld itself and no mind is paid the the joint construction. Now you sight Aircraft frames as a example of tig welding and 4130. Well again I call out joint construction, Frames are welded up using butt, lap, and fillet type welds, Go read your FAA spec book on welding and airframe it will state that and I quote "Rosette welds SHALL NOT be considered when determining the strength of the weld form" It's not that tig welding is bad it's that the joint construction is bad and is better suited to a riveted joint.
Like I said if the receiver was thinker sure I'd be all in favor of a welded rifle. I just don't feel that .03937" is strong enough after welding with no pre and post heat treatment to do the job as well as a properly riveted joint.

As for all the data you posted Go back and read your WPS in any structural application it will specify pre and post weld heating which is not being done on any home build weld thats for sure. You quoted 4130 specs in an annealed condition which is not what it will be after welding.
http://weldingdesign.com/archive/pos...etal-selection read that and tell me about pre and post heat.
Your HK reference is apples and oranges HK designed the weapon around welding in the trunnions and welding the seam of the receiver Better quality metals make a difference here.

The trunnion on an AK is made form god knows what and is very hard. I've had customers bring over trunnions that a repair was attempted by someone else and the weld chipped out and took based metal with it. So that tells me this stuff doesn't respond well to welding and special techniques need to be applied.

It does respond to welding if preheated and post weld controlled cooling is used

Now as to your post on stresses involved It's kind of moot, all this Pissing about welding VS rivets Yes there is very little stress AFAICT on the riveted or welded area. (I need to find that guy the PMed me about stress analyses and have him run this) In any event you'll notice I never said "dangerous" I just said a bad idea and I still feel it is. But if you wanted to use a reinforcement plate kind of like the back of a PSL receiver that would be much better then a supper thing chunk or sheet metal welded to a thick section and hoping for the best.

[Builder]

You mistake weld strength for superiority in joint construction.
Yes a tig weld is strong but it is too rigid for the application. The riveted joint is a flexible joint allowing the parts to move under stress and return to original position post stress. All I see here is an analyses of the weld itself and no mind is paid the the joint construction.

The joint construction of a rosette weld is an excellent way to join 2 parts if the loads (stress) are properly accounted for. Please understand that motion leads to wear. Proof of that is when a rivet or screw are not properly seated.

Now as to your post on stresses involved It's kind of moot, all this Pissing about welding VS rivets Yes there is very little stress AFAICT on the riveted or welded area. (I need to find that guy the PMed me about stress analyses and have him run this) In any event you'll notice I never said "dangerous" I just said a bad idea and I still feel it is. But if you wanted to use a reinforcement plate kind of like the back of a PSL receiver that would be much better then a supper thing chunk or sheet metal welded to a thick section and hoping for the best.

In the above analysis, the weld and HAZ stresses are initially fully able to handle the stresses placed upon them. That is not a bad idea.

The phrase that you might be looking for is work hardening. Repeated stress through a metal can work harden it. This actually strengthens the metal. Yield strength increase, tensile strength increases, but ductility decreases. Forging, rolling, extrusion, and drawing increase a metals strength. Reduced ductility can lead to embrittlement and cracking. Obviously, cracking reduces the load carrying capacity. Most cracking / post-weld brittleness occurs in the HAZ area, not the weld itself. But that is the reason for annealing post weld or by preheating to slow the cooling rate. Sometimes post-heating the weld to slow cooling further may be necessary. Rapid cooling is the worst. Each metal has a different work hardening progression.
http://academic.uprm.edu/pcaceres/Co...Met/MET-6A.pdf , see page 12.
In the case of the G3 using TIG welds to hold the trunnion into the receiver, it is neither dangerous nor a bad idea. A G3 recoil is greater than an AK.
As long as the initial stresses are accounted for and the reduction in ductility are accounted for, then a weld is more than adequate.
The reason a PSL has the reinforcement plate is that the receiver is not able to able to carry the loads, not the rivets nor any welds. 6 welds/rivets on the forward trunnion are adequate for both rifles. 4 welds in the AK are adequate for the AK recoil, while the PSL needs a thicker receiver to carry the loads of a higher recoil load while still using 4 welds. The rivets of both the AK and PSL are the same size so they are not the limiting factor. Same with the welds.
Thanks,
Builder
ps. Improper filler rod could be the cause of the poor welds you mentioned. http://www.weldingtipsandtricks.com/welding-4130.html We use ER70S-2 filler rod on mild steel.

[ar15barrels]

Here is one I built today with rivets:

[kcstott]

The joint construction of a rosette weld is an excellent way to join 2 parts if the loads (stress) are properly accounted for. Please understand that motion leads to wear. Proof of that is when a rivet or screw are not properly seated.



In the above analysis, the weld and HAZ stresses are initially fully able to handle the stresses placed upon them. That is not a bad idea.

The phrase that you might be looking for is work hardening. Repeated stress through a metal can work harden it. This actually strengthens the metal. Yield strength increase, tensile strength increases, but ductility decreases. Forging, rolling, extrusion, and drawing increase a metals strength. Reduced ductility can lead to embrittlement and cracking. Obviously, cracking reduces the load carrying capacity. Most cracking / post-weld brittleness occurs in the HAZ area, not the weld itself. But that is the reason for annealing post weld or by preheating to slow the cooling rate. Sometimes post-heating the weld to slow cooling further may be necessary. Rapid cooling is the worst. Each metal has a different work hardening progression.
http://academic.uprm.edu/pcaceres/Co...Met/MET-6A.pdf , see page 12.
In the case of the G3 using TIG welds to hold the trunnion into the receiver, it is neither dangerous nor a bad idea. A G3 recoil is greater than an AK.
As long as the initial stresses are accounted for and the reduction in ductility are accounted for, then a weld is more than adequate.
The reason a PSL has the reinforcement plate is that the receiver is not able to able to carry the loads, not the rivets nor any welds. 6 welds/rivets on the forward trunnion are adequate for both rifles. 4 welds in the AK are adequate for the AK recoil, while the PSL needs a thicker receiver to carry the loads of a higher recoil load while still using 4 welds. The rivets of both the AK and PSL are the same size so they are not the limiting factor. Same with the welds.
Thanks,
Builder
ps. Improper filler rod could be the cause of the poor welds you mentioned. http://www.weldingtipsandtricks.com/welding-4130.html We use ER70S-2 filler rod on mild steel.

You didn't read my post at did you??

[Builder]

You didn't read my post at did you??

Ok, I'll play along.
What part of a moving bond (rivet) do you find acceptable?
Thanks,
Builder

[kcstott]

Ok, I'll play along.
What part of a moving bond (rivet) do you find acceptable?
Thanks,
Builder

I'm not going to waste my time an energy trying to explain under what circumstances a rivet is not only appropriate but far superior to a weldment.

Do some research and you will soon figure it out. Not everything in mechanics benefits from a rigid mount

[valley82]

Maybe call Boeing and find out why they don't spot weld jets together instead of riveting...I don't know for sure but I would guess that it has something to do with the constant flexing during flight and the fact that welds would crack with the repeated flexing over time...

[Builder]

The assumption is a weld is TIG, not MIG, stick, or Ox/Ac.
Posts #24 and #25 both seem to confuse assembly technique with load carrying capacity (force).

The whole point of a rivet, weld, screw, or glue is to carry loads across a joint. If the bond moves, then this introduces friction. Friction leads to wear. Wear leads to failure. Failure is not acceptable.

Just so everyone knows, a weld and HAZ can be made as strong as the base metal. It requires annealing and heat treating. A weld builds up stresses in the metal and these stresses reduce ductility. When flexed (stressed) repeatedly, this leads to cracking and eventually failure. Assume an untreated HAZ has around 50% of the strength of the base metal.

A simple method to calculate the shear strength of a rivet is :
Cross-sectional area times shear strength.
Shear strength is 75-80 % of tensile strength for steels.
Since we must deform the rivet, we have mild steel rivets, so a 60,000 tensile number is ok.
Therefore the rivet will shear at 45,000 psi.
The cross-sectional area of an AK rivet is no larger than 0.024 inch http://www.k-var.com/shop/Rivets-sp-34
(Area = Radius Squared x Pie or)=.00765 x 3.14 = .024 sq. in., then .024 sq. in. x 45,000 = 1,080 pounds of force to shear.
3/16" stainless pop-rivets can almost do that!

So if we compare this to the weld calculations that were done in post #18, a proper weld is an acceptable replacement for a rivet. Improper welds are equivalent to improper rivets. As a foot note, more than 6 rosette welds can be done on the trunnion thereby reducing the loads through each weld. Is that possible with the rivet technique?

A medium caliber rifle's recoil energy is below 50 ft-lb.
Thanks,
Builder

[kcstott]

Yes but your weld calculations are incorrect

[Builder]

Thank you for finding the typos. It should be 2031 lbs., not 2051. It should be 781 lbs., rather than 750.
Principle still stands regardless of the typos.
Thanks for reemphasizing the point that rosette welds are strong enough,
Builder

[bigbob76]

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.

[kcstott]

Thank you for finding the typos. It should be 2031 lbs., not 2051. It should be 781 lbs., rather than 750.
Principle still stands regardless of the typos.
Thanks for reemphasizing the point that rosette welds are strong enough,
Builder

Thats not what I was getting at. Your fundamental calculation is incorrect.

But Like I said if you want to weld up your trunnions you go right ahead. I'm going to stick this rivets and period correct construction methods