Can someone explain to this old dinosaur just what TIG welding is? I've heard it can be used to fill pits on the exterior of barrels, frames, etc. Doesn't the heat required cause metal distortion? I've heard the term bandied about but really have no idea of what is involved in the process. Thanks loads! Chopperlump
TIG means tungston inert gas, you hand feed the filler metal into the arc which is under a shield of argon gas. The arc comes from a sharpened tungston electrode A real picky welder will mix 5% hydrogen with his argon so it will burn any oxygen leaking into the shielded area. In industry parts are often simply fused together without filler. The heat affected area can be quite small.
bill
What are the bluing properties/characteristics of the welded areas?
I'll show my ignorance here as well concerning the tig welding of pitted barrels and actions! Does the size of the pit matter? Is a small bead put in each individual pit, or is a bead layed on over the exterior of the pitted area and then filed down to match the contour of the barrel?
I just can't visualize in my mind's eye!
Thanks
Cam,
Generally, each pit is welded up individually. The surface should be clean and free of rust or any guck. Chemical cleaning and/or mechanical is used to either etch rust/corrosion or grinding with a rotary burr to remove any potential contaminants. Once welded up a barrel, I normalize the weld and the adjacent area by heating with a welding torch since I've encountered hard spots directly adjacent to the welding on some barrels. Then filing can be done without any difficulty.
Any clue as to the blue aspect? I've heard that rust blue will show the tig(ed) areas... Anyone tried rust blue after weld build-up?
The bluing properties would depend on a careful match of base metal (barrel, action, etc.) and filler rod. Hard spots would depend on how the base metal alloy reacted to the heat of the welding. Since pits are generally small (both size and volume), the amount of heat and hot metal is small relative to the size, shape, and volume of the base piece. So, this work can be generally done without warpage. The "smallness" of what can be done is pretty amazing. BTW, I predict a pretty good market for the first guys that do good barrel bore pit filling.
sometimes hot blue shows the different metal, but rust blue is usualy the same color across the board.
TIG allows you to do very precise welding and not use an obscene amount of heat on the part. You have more finesse with a TIG rig than any other kind of welding, so you can do things such as weld individual pits, weld 2 razor blades together, and other very detailed work.
I use pure argon, as does every other custom maker with whom I have spoken. Also use 1/16" 2% thorinated tungsten and 1/16" filler rod of various alloy. I also use a foot control rheostat for the amperage. You can weld with as little as about 5amps of current. This allows you to add just enough heat to the part to get the puddle and fusion you need, but no more.
Another benefit is that welds are very "clean," assuming you haev done everything correctly. This is critical when doing highly finished custom work.
TIG has replaced oxy/acetalene welding in gun work just as forge welding was replaced many, many years ago.
On the barrels I welded, apparently they had enough carbon to harden when the weld 'self-quenched', a characteristic of TIG welding.
Chuck is correct that the small welds generally "self-quench" due to the "heat-sink" nature of the large mass of surrounding steel. I find it much better to stone the weld down to final dimensions as the weld is often so hard that files almost skate on it.
I am going to be welding up some barrel pitting for a member of this board. I will post some pictures of the process and some before and after pictures next week.
Bill G.
BTW,
A weld on most things will have very high stresses after cooling. Best to normalize with a torch to also stress relieve the weld.
I have done a fair amount of gun welding with TIG and can comment on the bluing aspects. I have found that rust blue will cover very well on 4140 and similar chrome-moly parts welded with Brownells 3% nickel rods. Occasionally, if held up to the light just right, you might see a slight tonal variation. A thin oil film usually make it invisible.
On mild steel like a Win '92 or Mod 61 receiver, the welds will show when hot blued and it doesn't matter what you use for filler rod. If you rust blue the same guns, the welds are truly invisible.
I can't comment on Carbonia blue coverage, but I wish someone would. Turnbull couldn't or wouldn't offer any assurnaces.
OB
Preheating your weld area is good. I don't remember my metalurgy lessons that well please let me know if I have this wrong. If you water quench your parts after the weld your steel will remain the same hardness as it was prior to welding. If you air cool or just let the part cool on its own you weaken the metal around the weld. The problem is in the Filler. Unless matched to each gun it will almost never be exactley the same hardness.
Interesting information guys!
Thanks Chuck for the description on how its done.
Bill G. I look forward to viewing pictures of the process.
I have been doing some restoration work on some old guns of mine that have needed it for years. Their finish is too far gone to worry about their collector's value, but they function well, are accurate and do the job. So I've been restocking them and plan to send them to my gunsmith for metal finishing. Some of the guns have minor metal flaws and minor pitting, as most of them are approaching 100 years in age. I have recently discovered a gem of a technician who does microwelding for the manufacturing industry. He has both TIG and laser welders. For the really fine jobs, his laser welder can add as little as two thousanths of an inch of metal to fill in a pit or correct a flaw. There is no issue of overheating the metal, as the heat is so localized. He actually welds in an inert gas (argon) glovebox with a built in binocular microscope. His rods are so tiny they remind me of music wire. One job he did for me was to build up the metal on a stripped-out 6-48 screw hole so that it could be retapped. He actually welded additional metal on the threads inside the hole! He is using low carbon steel rod for my gun jobs, so I anticipate no issue color changes using rust bluing. Microwelders are a rare breed, but if you can find one who will work on guns, he can do wonderful things.
The metal properties after welding depend on the alloy AND the quenching process, if any. Remember, the only difference between annealing and quenching is the alloy and the cooling process. It is quite easy to greatly LOWER the strength of the entire structure by employing seat of the pants "normalizing".
Welding and heat treatment are a science, WHEN DONE CORRECTLY. What Bill said about hydrogen is spot on, and I haven't heard anyone mention that in at least three years.
Unless you are willing to invest enough time and effort to get well beyond the "bit of knowledge is a dangerous thing" phase, I would strongly advise utilizing the services of a proven professional for this type of service.
Also, remember that metal alloys have changed over time, not because the specs have changed, but because steelmakers can more closely match specified minimum alloy content(s), and thus reduce their costs, while incurring small risk of producing off-quality steel that is out of spec. They used to have to be much more generous to make sure they ended up well within spec.
Virginian,
You are right. The only "correct" way to weld something like this is to weld, stress relieve in a heat treat oven and re-HT. But that's impractical. So, it's a choice of two bads; whether to leave a weld with obvious high stresses and hardness or 'seat of the pants' normalize it. You may recall, this assembly of barrels is silver brazed at the chamber end. I'm guessing it was done with a torch in 1900. Also, barrels on the vintage guns I've worked on were of very low hardness and heating them wouldn't likely lower strength significantly. It's common to stamp maker names and engrave scroll and gold inlays into the outside of a barrel chamber, which is probably as an bad a thing to do as welding this area.
One additonal thing, I TIG'd a sleeving job on a LC and had hard welds/adjacent areas and had to torch normalize it or figure out how to cut the chambers with something better than HS steel reamers. From personal experience, I can tell you the barrels will have spots hard enough to take the edge off a Clymer HS steel reamer if you don't normalize. In that bottom pic, I'm about to remove the edge on that $180 Clymer reamer. Fortunately, I have a friend in the cutter manufacturing biz and he had another friend specifically in the reamer biz fix the forcing cone portion that got dulled.
BTW, metal specs were nearly non-existant, proprietary formulas in 1900. You won't find 4000 series chromolly (todays common barrel material) until the War years, WWII if I recall. Serious efforts to standarize metals in the US happened in the period just before and during WWII.
