Gas system unitization via TIG weld ?

Murray 3-D

Murray 3-D

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Bought a M305 with various GI parts, noticed the front ferrel and gas cylinder need re welded (it was once unitized), one of the welds was cracked when i bought the rifle. Fortunately for me i have a welder at work willing to help me with this.

For what ive read on here, TIG welding seems to be the go to for this procedure since it offers the best bond between the 2 parts ? Vs 3 simple tacks with a MIG ?

I also read that its a great benefit to create a jig that holds the 2 parts uniformly together for the welding process, anybody have any pointers I should incorporate into the design for the jig?

And finally, i read for TIG rod, somebody suggested 416 stainless, is there any other rod recommendations ? Is rod selection really critical for this task ?

Thanks for any insight.
 
I would just use an ER70S mild steel rod. i have one gun with lots of rounds through it, and no sign of cracking. I don't think the rod needs to be anything special. Grind off the old cracked weld. Wipe it down with acetone. Might need to use a Dremel with a mini cutting disk. Preheat the whole thing with a bit of heat from a propane torch to minimize distortion as the weld cools. Not sure about the jig. I just weld them right on the rifle, but that's probably not the best procedure.
 
+1 for pre and post heat. It definite is a must. I also would try and match the filler wire you're using to the base metal. Im pretty sure the original m14s used 8620 steel, which I imagine china used as well. So a 416 stainless isnt appropriate here. TIG is a good option for this as well It will allow you to control the amount of heat you're putting into the weldment easier than a few tacks with mig(even though this may work too)
 
Uhh, unless what you're welding is made of stainless, don't use stainless filler. You want the composition of the filler rod to be as close to the base material as possible. TIG will definitely give you better control if you're trying to weld small intricate sh!t, but your guy has to know what he's doing. Blobbing MIG welds on there might be easier, but you really have no way of knowing if you're getting decent penetration or not. With the right settings and thin enough wire, MIG could work. But TIG is likely your best bet.
 
no preheat in this situation
yes build a jig... very important. Jig must act as a barrel holding the components in place and also must have a feature to evenly clamp the gas band plate to the cylinder.
Yes you should dress the weld locations on both sides with a small file to remove Parkerizing.
Yes you should thoroughly clean the parts with brake cleaner before welding.
Use a chromoly filler rod on Norinco cylinders and 416 stainless on USGI cylinders
the welds are 3/16 fillets at 10, 2 and 6 oclock.
After welding leave cylinder in jig and wrap with leathers to afford a slow cooling process.

We've done easily over a hundred , maybe close to 200 gas system unitizations with the TIG method in my shop when it was open and at the many clinics I put on over the years so take my advice for what it is worth.
I was also a steel fabricator/fitter/welder for Magnum Custom Steel Fab in a previous life and my TIG welder is a 30+ years in the trade , pipefitter/gas fitter and specialized in stainless process piping his entire career.

an no.... MIG and stick welding these parts is a big no no.
TIG only.
 
Your results speak for themselves, 45acpking, but why no preheat? There should be less distortion and stress at the weld with preheat. Its the temperature differential between the puddle and the surrounding metal that produces differential in shrinkage as the weld cools vs the base metal.
 
Grizzlypeg said:
Your results speak for themselves, 45acpking, but why no preheat? There should be less distortion and stress at the weld with preheat. Its the temperature differential between the puddle and the surrounding metal that produces differential in shrinkage as the weld cools vs the base metal.
Click to expand...

preheat allows more heat transfer or build up and this is not desireable.
In the beginning when we were experimenting , prior to subjecting customers parts to modifications, preheat was what we though was a no brainer. What we found though was that things just ended up too hot and we got subtle undesirable affects, the worst of which was mild chrome flaking in the Chinese cyclinder tube near the bottom weld and it also appeared to warp the cylinders slightly out of true.... causing piston wear that would otherwise never happen.
When we dropped the preheat and also allowed a slow cooling under the pressure of the jig, these undesireable results never appeared again.
With USGI cylinders there is no chrome lining in the cylinder itself so perhaps not an issue but still the risk of warping the tube remains.
I am not a TIG welder, I'll say that right now, so I deferred to my expert Tig welder to find and apply the best process for professional results my customers at the time would be happy with. Folks seem pretty happy with the end result and I can't recall any complaints.

Another method of unitizing is the screw and glue method and some folks prefer it but it is difficult.
 
Thanks for sharing the experience that led you to that opinion. I note that my book, The Duff and Miller, says nothing about preheat either. The do mention using a copper rod in the cylinder as a heat sink, along with a heat transfer paste.
 
back in 2008 I think..... when I lived in Langely and was doing clinics out of the house, a cgn member who's name I have long forgotten, gave me a unitizing jig he made up.
That jig is an amazing tool and I'll try and describe it

A brass rod approx. 5" long and 3/4" diameter, at one end it was squared off so it could be clamped in a vice.
The body of the rod was turned in steps. The first step was the same diameter as the gas system port buttress so the cylinder fit as it would on the barrel and the gas band plate held tight against the brass rod at the shoulder. Then the rod was turned with another 90degree shoulder to a diameter that "just" clears the splines in the 2nd ring of the gas system. The end face was turned to match cylinder OAL and bored and threaded for a washer and bolt.
The second part of the jig consists of a 3/4" copper tube and copper end cap. These are soldered together and trimmed to the length of the cylinder body, from end to gas band location. The copper end cap is drilled to accept a 1/4" bolt that is longer than the gas cylinder. The bolt has washers on each end.
The copper tube is placed over the rear of the gas cylinder tube and the bolt carefully passed thru the end cap and cylinder. Apply a sturdy washer of appropriate size and gently bring to snug. The brass rod and copper tube fasteners be should tightened evenly and firmly but not "gorilla tight" if you get what I mean. You don't want to put so much pressure that you put any thing under stress.
adjustments to the band are made before final tightening of course.

I'll dig around for pics but I passed that Jig on a few years ago when I stopped working on rifles
 
45ACPKING said:
no preheat in this situation
yes build a jig... very important. Jig must act as a barrel holding the components in place and also must have a feature to evenly clamp the gas band plate to the cylinder.
Yes you should dress the weld locations on both sides with a small file to remove Parkerizing.
Yes you should thoroughly clean the parts with brake cleaner before welding.
Use a chromoly filler rod on Norinco cylinders and 416 stainless on USGI cylinders
the welds are 3/16 fillets at 10, 2 and 6 oclock.
After welding leave cylinder in jig and wrap with leathers to afford a slow cooling process.

We've done easily over a hundred , maybe close to 200 gas system unitizations with the TIG method in my shop when it was open and at the many clinics I put on over the years so take my advice for what it is worth.
I was also a steel fabricator/fitter/welder for Magnum Custom Steel Fab in a previous life and my TIG welder is a 30+ years in the trade , pipefitter/gas fitter and specialized in stainless process piping his entire career.

an no.... MIG and stick welding these parts is a big no no.
TIG only.
Click to expand...

So probably listen to this dude. Lol.
 
I turned out a nice jig on the lathe last night, it may not serve as a very good heat sink, but it does certainly do the job of keeping the two pieces clamped in perfect alignment.

Hopefully ill have it tig welded within the week. I want to have the rifle built in time to attempt Riflechairs Cabin Fever Challenge.
 
WOW

The gas cylinder is of 400 series stainless steel.
The front stock ferrule is of tempered chrome moly.

Any pre heat as mentioned in previous posts will remove temper in both parts & as would any post heat treatment.

TIG fixture-
My fixture fits inside the front ferrule & is clamped into place w/ a 1/4-28tpi allen head cap screw w/ aluminum washers to sandwich the parts for perfect alignment.
Another aluminum collar is slipped onto the gas cylinder to back up the opposite side of the front stock ferrule.
A piece to 360 brass is inserted w/ purge holes into the gas cylinder w/ 10 cubes of purge flow while welding.
The gas spindle valve/spring/roll pin is removed & plugged w/ a piece of turned 360 brass.

Any parkerizing has to be removed from the parts prior to TIG welding.
Fillet TIG welds are located at 6 & 12 oclock position of the assembly.

Match the filler to the largest parent material (cyl) or you're wasting time & money chasing cracks.
.030"308 stainless mig wire as a TIG filler rod/wire will not rust or crack accomplishing this simple task.

Hundreds & hundreds & hundreds unitized to date in the last 30+ years w/o issues.
 
DANS40X said:
WOW

The gas cylinder is of 400 series stainless steel.
The front stock ferrule is of tempered chrome moly.

Any pre heat as mentioned in previous posts will remove temper in both parts & as would any post heat treatment.

TIG fixture-
My fixture fits inside the front ferrule & is clamped into place w/ a 1/4-28tpi allen head cap screw w/ aluminum washers to sandwich the parts for perfect alignment.
Another aluminum collar is slipped onto the gas cylinder to back up the opposite side of the front stock ferrule.
A piece to 360 brass is inserted w/ purge holes into the gas cylinder w/ 10 cubes of purge flow while welding.
The gas spindle valve/spring/roll pin is removed & plugged w/ a piece of turned 360 brass.

Any parkerizing has to be removed from the parts prior to TIG welding.
Fillet TIG welds are located at 6 & 12 oclock position of the assembly.

Match the filler to the largest parent material (cyl) or you're wasting time & money chasing cracks.
.030"308 stainless mig wire as a TIG filler rod/wire will not rust or crack accomplishing this simple task.

Hundreds & hundreds & hundreds unitized to date in the last 30+ years w/o issues.
Click to expand...

Dan, you realize most of ours are Norincos, (Polytechnics to you Americans). Do you have experience on them?
 
This is and old post. These are now banned in Canada so I wouldnt take them anywhere to get the welding done. So unless you can do this in your house your screwed
 
Last edited:
Komodo said:
This is and old post. These are now banned in Canada so I wouldnt take them anywhere to get the welding done. So unless you can do this in your house your screwed
Click to expand...

Could I would think take barrel and gas system to someone for welding. Probably should leave receiver at home
 
OK yep you could take the receiver off . This would have to be done at home . I dont have the tools or technology at home to do that
 
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