bolt carrier damage....

[netpackrat 566]

Regarding the Gas welding, I've looked into it more, and yes you can gas weld chrome alloys, but the problem with this is generally on aircraft welding, bike frames and such, where it is traditional to do so, filler being used does not have a equal chrome content. The process relies on the filler metal to draw some chrome from the base metal to normalize Base and Filler material into a near equal strength.

 

This being said while great in many applications, you are taking a step closer to a mild steel or carbon steel by drawing out chrome from the parent material.

 

Tig welding has the benefit of carrying over additional chrome in the filler metal, and more localized heat.

 

Due to the lower temps used in gas welding and the wider spread of the heat Gas welding would not require heat treating following the weld, where TIG often calls for it.(though I believe on something so small you might be able to get away with wrapping it in a fire blanket to hold the heat in and slow the cooling process)

 

I wouldn't feel comfortable Gas welding it, If you do, Its your gun. Post up results and a follow up after a few hundred rounds.

 

 

TIG or gas won't make any difference in terms of affecting the chrome content of the metal. The torch just provides a source of heat, whether that is an electric arc in the case of the TIG torch, or a chemical reaction in the case of the oxy-acetylene torch. In aircraft welding we do use a mild steel filler rod on 4130 tube frames, but we use a mild steel filler whether welding with TIG or the gas torch. Anytime a weld calls for 4130 filler rod, it will also call for the entire part to be heat treated following welding, regardless of the method used to make the weld. Tube frames are usually too big to go into a heat treat oven, so we use mild steel filler to avoid cracking in service due to too much hardness in the joints. The size of the joint reinforcement (weld beads) generally makes up for any dilution of alloy in the joint (this is why super tiny, pretty TIG welds are not necessarily your friend).

 

As you noted, the more localized nature of TIG heat can be either a blessing or a curse... In the case of a highly stressed joint, it can be a detriment because the heat affected zone is left closer to the highly stressed area, which can lead to premature joint failure. In other applications, the more localized the better, because it keeps the heat from affecting other areas of the part. As a practical matter, on many smaller parts it matters very little, because when you finish welding, you'll find the entire part glowing no matter which method you use. I would expect that to be in play here, because while obviously the main part of the carrier isn't going to be affected, due to the small size and mass of the part that the operating rod threads into, with either method the heat affected zone will most likely be moved down out of the most highly stressed area where it cracked in the first place.

 

As an aside, you mentioned the term normalizing. In welding, that term doesn't refer to the alloy content of the joint (i.e. mixing of base and filler metals), but to the state of heat treatment. Normalizing is what you get, when a piece of steel is heated to welding temperature, and then allowed to cool in still air. The result is less hard than hardened steel, but harder than annealed. For example, the chrome moly steel used in aircraft construction is generally supplied from the mill in a normalized state. The reason for this, is so that it has more or less the same strength after fabrication and welding, as it started with. That helps to ensure that the designer's stress calculations are reliable.

[Nailbomb 10,221]

 

 

TIG or gas won't make any difference in terms of affecting the chrome content of the metal. The torch just provides a source of heat, whether that is an electric arc in the case of the TIG torch, or a chemical reaction in the case of the oxy-acetylene torch. In aircraft welding we do use a mild steel filler rod on 4130 tube frames, but we use a mild steel filler whether welding with TIG or the gas torch. Anytime a weld calls for 4130 filler rod, it will also call for the entire part to be heat treated following welding, regardless of the method used to make the weld. Tube frames are usually too big to go into a heat treat oven, so we use mild steel filler to avoid cracking in service due to too much hardness in the joints. The size of the joint reinforcement (weld beads) generally makes up for any dilution of alloy in the joint (this is why super tiny, pretty TIG welds are not necessarily your friend).

 

As you noted, the more localized nature of TIG heat can be either a blessing or a curse... In the case of a highly stressed joint, it can be a detriment because the heat affected zone is left closer to the highly stressed area, which can lead to premature joint failure. In other applications, the more localized the better, because it keeps the heat from affecting other areas of the part. As a practical matter, on many smaller parts it matters very little, because when you finish welding, you'll find the entire part glowing no matter which method you use. I would expect that to be in play here, because while obviously the main part of the carrier isn't going to be affected, due to the small size and mass of the part that the operating rod threads into, with either method the heat affected zone will most likely be moved down out of the most highly stressed area where it cracked in the first place.

 

As an aside, you mentioned the term normalizing. In welding, that term doesn't refer to the alloy content of the joint (i.e. mixing of base and filler metals), but to the state of heat treatment. Normalizing is what you get, when a piece of steel is heated to welding temperature, and then allowed to cool in still air. The result is less hard than hardened steel, but harder than annealed. For example, the chrome moly steel used in aircraft construction is generally supplied from the mill in a normalized state. The reason for this, is so that it has more or less the same strength after fabrication and welding, as it started with. That helps to ensure that the designer's stress calculations are reliable.

 

Why wouldn't something as expensive as aircraft take advantage of ceramic heating pads for pre and post heat treating on chrome like I've often used in my work? No need to drag the whole frame into a oven...

 

 

Or on a smaller scale(more time lest equipment cost) a rosebud and temp sticks can be used to do it the old fashioned way.

 

As a aside, if your actually mixing the metals and not just laying one over the other unbonded, when using a different alloy filler you always change the content of the base metal at the joint. Even just heating chrome can effect the content, this can be seen as sugaring in overheated metals. While this is more predominant with stainless I have seen high chrome content welds call for a backing gas for this reason.

[Paulyski 2,227]

With regards to torch welding a carrier, the steel has both chromium and magnesium, both of which are there to prevent oxidation.
It's not quite as resistant as a full on stainless such as 308 or 316, but still, it resists being torch welded because of this.

I've tested the theory with a decent torch, if a Victor J-100 with #1 Victor tip is decent in people's eyes...I always heard Victor was about as good as one gets. My tip makes a very sharp point, but regardless of heat, it just doesn't make a good puddle.
Sure, heat something up enough and the steel will melt, but it just doesn't make for a controllable puddle, so it's just not the most ideal way to go about it for proper fusion.

If it were mine, I'd stick weld it using 3/32" e309L @ 80 amps with a threaded brass rod screwed in WAY before gas welding it if one lacks tig.

 

But there's always multiple ways to skin a cat.

[MegamanX 65]

This thread has me concerned for the integrity of my carrier now.

[netpackrat 566]

Why wouldn't something as expensive as aircraft take advantage of ceramic heating pads for pre and post heat treating on chrome like I've often used in my work? No need to drag the whole frame into a oven...

 

Or on a smaller scale(more time lest equipment cost) a rosebud and temp sticks can be used to do it the old fashioned way.

 

As a aside, if your actually mixing the metals and not just laying one over the other unbonded, when using a different alloy filler you always change the content of the base metal at the joint. Even just heating chrome can effect the content, this can be seen as sugaring in overheated metals. While this is more predominant with stainless I have seen high chrome content welds call for a backing gas for this reason.

 

 

Cost. Contrary to popular belief, most of the people who own airplanes are not wealthy, and tend to be guys like us who have set being able to fly as a priority in their life. Chances are they drive an older car, and gave up having the nice gun collection in order to afford that airplane. Also, aircraft that are built with tube frame structure tend to occupy the lower end of the cost spectrum.

 

The 4130 alloy that is most commonly used to build airplanes was designed to be welded using a gas torch, decades prior to the advent of TIG. As I said, it is delivered from the mill in a condition designed to assure that it is mostly the same after welding as it was before. There is little point to using a rosebud when O/A welding a tube frame (unless working a big cluster joint and you need the extra heat), because the less localized heat naturally moves the affected zone away from the most highly stressed areas. There's actually a lot of controversy regarding TIG on 4130 tube frame structure, because it can leave the affected zone in the stressed area, which has sometimes led to cracking in service. So actually it is not uncommon to post-heat joints with a rosebud after they are welded with TIG.

 

It's a lot less high tech than most people outside of the industry (or hobby) tend to assume. You can literally build a fuselage in your garage that is as good as one built in a factory, and I have flown in some of those airplanes. What's more, is the structure needs to be repairable in the field, and few (read: no) shops are going to have a heating setup like the one pictured, and no aircraft owner is going to agree to re-doing an entire fabric job to make a localized repair. Particularly up here, it is not uncommon to have to make repairs in remote locations, where you have to fly tanks and a torch in to an incident/accident site. While TIG machines now are probably small enough to do this, they still haven't invented a long enough extension cord to run them.

 

Furthermore as far as chrome content preventing oxidation, I have not observed that 4130 is any less prone to rust than regular mild steel.

 

Back to a Saiga carrier, I will of course have to defer to Pauly's knowledge of the specific alloy the Russians used, but I will maintain that the method of heating won't have much effect on the chrome content of the base metal (assuming a properly adjusted neutral flame). That will be determined by the specific filler used, and I wouldn't doubt that it has a different requirement than the aircraft tubing I am used to working with. It would definitely be harder to do with the gas torch just based on the geometry of the part, and TIG would still be my first choice. But I wouldn't despair of making the repair if all I had was a torch setup.

I've tested the theory with a decent torch, if a Victor J-100 with #1 Victor tip is decent in people's eyes...I always heard Victor was about as good as one gets. My tip makes a very sharp point, but regardless of heat, it just doesn't make a good puddle.

Sure, heat something up enough and the steel will melt, but it just doesn't make for a controllable puddle, so it's just not the most ideal way to go about it for proper fusion.

 

Victor makes a decent torch as far as general metalworking goes, but for precise work it's hard to beat a Meco Midget with the ultralight hoses. I took a course a few years ago where we gas welded (and brazed) aluminum sheet with oxy-acetylene, and that was what the instructor brought for us to use. I know a number of people who have used them to build their airplanes.

Edited June 14, 2013 by Netpackrat

[alistar 13]

Fascinating technical stuff, but way beyond my abilities. Tom as always stands behind his work and sent back a repaired carrier that looks very good. The R and R works perfectly for at least the first 160 rounds of birdshot and 5 of 00 buck. I don't know how its steel differs from Izhmash but suspect that it does.

 

As for the design, I don't know why the end tapers down around the piston attachment, there is no need to have the area so thin.

 

Bottom line imo and experience is that if the S12 fills an important home defense or business niche, then having a second bolt carrier/piston rod makes sense.