Gas Welding Screwholes in Barrel
I have a botched scope mounting hole in a .257 rifle barrel (broke the tap and then it got worse....). Can I weld it up using a hobby oxy-propane torch with nickel steel rod? If the weld is good, will the barrel be affected in any way (ie the heat treatment). I know that TIG is the standard answer but I don't do TIG. And does anyone know how to get around those miserable $8 bottles of oxygen that come with bernzomatic torches? Either an adapter to something that lasts more than five mins, or a way to refill? mailto:russ@canby.com
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I don't do TIG or MIG either, and have often wished I did; but I can try to help a little. I'm going to assume, unless you correct me in a subsequent post, that the holes you were drilling are in the receiver--the receiver ring and the bridge at the rear of the receiver. I haven't seen too many drilled and tapped barrel-mounted scope set-ups. Welding on a barrel will usually cause the barrel to warp or distort--so I'll hope that's not the case. If it is, I have a different approach for your consideration. Going with the assumption, have you heard of Brownell's Heat Stop Paste? Great stuff. It comes in a plastic jar and looks like grey mud. Apply a ring of it around the barrel just forward of the receiver ring, and you can heat the receiver ring red hot (not a good idea!) and hold the barrel 4-6 inches on the other side of the heat paste ring with your bare hands. Very effective. As far as getting the broken tap out, they make tap removal tools that consist of small metal fingers that go into the flutes inside the hole. Sometimes you can turn them out, and sometimes not. You can also sometimes turn them out by tapping against the flute in a counter-clockwise direction with a hammer and small punch. Sometimes (after the first two have failed) you can use a sharp, pointed punch and shatter the tap stub a piece at a time with sharp blows. Sometimes heating the surrounding metal and expanding it away from the tap helps. A good application of a penetrating oil helps before trying to mechanically turn one out. They can also be burned out with an electrode, but that's beyond the hobbiest (and me too). In any event, it would be best to remove the tap before doing any hole filling by welding; especially if it is your intention to drill a new hole in the same location. Yes, nickel steel rod is the best way to go. Use a small torch and get the edge of the hole hunter orange red. Stick the end of the rod into the hole and melt it and use a continuous circular swirling wrist/torch motion. The hole will fill; and be sure to fill it a little above the level of the surrounding metal, because sometimes the filling metal will subside into the hole a little as it cools and contracts. File the excess off. Use the heat stop paste liberally to avoid the heat spreading beyond the immediate work area and altering your heat treatment. Some clues for next time: Always use a brand new tap for each job. The temptation to re-use them over and over will get you into trouble. The cost of a new tap is cheap insurance. Use plenty of tap fluid, and be sure the can says that it's for steel and not aluminum (unless you are tapping aluminum--in which case the fluid is a different formula). As you turn the tap in and begin to feel resistance, stop and turn the tap back the other way a couple of turns. This breaks the chip that is being formed in the flutes as a result of the cutting action. Squirt in more fluid and resume cutting until the resistance again becomes stiff. Sometimes it's prudent to completely back the tap out of the hole and remove the chips from the hole with the magnetized tip of a machinist's scribe or other sharp pointed tool. Clean the tap off with a toothbrush before going back into the hole. Taps break easily if the tap isn't held perfectly vertical to the hole, and tap guides are available to assist in keeping the tap vertical. I can't help you with the hobby sized oxygen bottle part of your question, as I use regular sized welding tanks. Good luck--we've all broken a tap or two before! 0 -
Hello, can you post a picture?
Michael
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Another tip...I have learned that some receivers are hardened to the point they either won't drill, or if they drill, they're too hard to tap...without the danger of breaking the tap....Apply heat to cherry red...with a very small tip... right down the hole. Then let cool slowly.. the hardness disappears (annealing) and tapping is a lot easier... To fill a threaded hole, drilled out of line,plug it with a threaded plug.. all the way to the bottom of the bad hole.. leave the top of the plug below the surface, about 1/16 to 1/32"and then tig weld the remaining shallow hole, fusing the plug to the sidewalls. Recontour the surface..layout and re-drill . The weld will hold the threaded plug in place, it will allow recontouring of the surface, and the shallow hole to be welded will assist in minimizing heat applied.. You don't want to anneal the entire receiver... Good luck...... 0 -
Best way is to have the tap EDM'd out. Take your rifle to any good machine shop. If they don't do EDM, they know of somebody that does.
It'll probably cost you $25-30.0 -
Some very good advice above. I would add a couple items. If can get the broken tap out you can just plug the hole and make an almost invisible repair. If needed to get a clean surface, you may want to start a tap the next larger size just enough to get a thread into the hole. Then screw in a screw till it binds tight against the tapered bottom of the new thread. Cut off the screw about 1/32" above the surface and carefully tap it so as to spread it into the hole and fill it out. If unable to get the tap out, I recco taking the job to a gunsmith who has MIG or TIG ability and have him weld over the area. Either way then finish it off down to the surface. Carefully done the job can be spot refinished without doing the entire barrel or receiver, whatever. Hope this helps. 0
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