Repair of Deep Pitting

PhilOhio · 07-09-2009, 01:42 PM

Gentlemen,

Thanks for the responses. As Ed suggests, repair of major pitting is never likely to be a cost effective undertaking. I do it (rarely) because I enjoy it and can, if I have the time and really want to. My primitive method has been to bead blast and then overlap a series of weld beads using 1/16" rod at about 50 to 55 amps with a conventional arc welder. All "hits" are less than one second, so good visibility and an instant auto-darkening helmet lense are essential; can't be done any other way. But this is very demanding and difficult. And then you have to do some delicate machining and/or grinding to get back to a level surface. TIG would be much better, but I don't have that gear.

On rounded surfaces, it's tough, unless you can mount the weld-filled piece in a metal lathe and turn it back down. So it can be done with barrels. I did it with one of my Thompson barrels years ago...a barrel which a professional gunsmith had badly carved up with a hacksaw, besides the pitting, because that was the easiest thing to do when removing it, and he didn't think the barrel was worth much; "then", that is.

The easiest part of the whole job is putting on the blue or parkerizing; so far, I've always gotten a perfectly blended match, as long as there is no nickel or chromium in the original gun alloy or the welding rod used for filler. If you use the wrong rod, no way will you match it, although you can cover it over nicely with one of the modern spray-on finishes...but not on a Luger.

Guys, have I learned a lot after a few hours of Internet research yesterday. There is a much better and easier way to do all this if you have access to certain modern technology, which is rather widely distributed.

There is a process called "arc thermal spraying", and there are about three other closely related processes. All involve using clean dry air, or an inert gas, to blow liquified droplets of metal onto your pitted surface, which has been sand or bead blasted and made very clean.

Before solidifying, the droplets flatten and overlap. You have perfectly fused new metal, much like welding, if you did it right.

One of the best part is that the substrate, your gun or gun parts, get barely any heat. They are not warped or distorted. And because of the lack of a heat threat, you can use certain masking tapes to mask off your pitted area, as though you were spray painting; which is exactly what is being done.

Some versions of the equipment dispense powdered metal and others use two wire-feed electrodes which arc, to produce the droplets. All versions do the same thing, build up your surface with newly fused metal droplets.

Much of the equipment consists of small, very portable components; it's intended for field use on damaged equipment or parts. I think most of it looks too expensive for basement hobbyist use, but quite a number of small repair companies have it and advertise that you can send them your gear for repair, at reasonable cost. I would imagine that could include gun parts. I expect that in most urban areas somebody has this stuff.

Almost any metal works. It is being done with steel, brass, aluminum, and a variety of alloys including monel and even carbide, for restoring large cutting tools and such things as scraper blades and industrial teeth of various types.

Sounds to me like some miraculous fun technology, and I thought some of you might like to know. People are offering these services all over the net. Do a search on "arc thermal spraying".

Oh, yes, sorry I did not save the url, but the U.S. Navy is into this in a big way, for repair of everything under the sun on ships, from small stuff to hulls. On the net, I found publication of the Navy's wonderful overview training manual for explaining to new maintenance trainees what main technologies are out there (four, I believe), how they work, and very precisely how you do it yourself...and what to avoid.

For those of you who are incurable restorers, as I am, I hope you enjoy looking into this on the net. It's something to keep in mind, next time you have a worthwhile collector firearm which may be in pretty good general condition, except for a very localized area of deep pitting damage; send it out for a minor skin graft.

What would be really neat is if there were a version of this sprayer small enough to use like an air brush. Maybe there is. The ones I saw were about the size of a gun you would use for spray painting a car.

07-09-2009, 01:42 PM	#4
PhilOhio User Join Date: Apr 2009 Location: Ohio Posts: 145 Thanks: 5 Thanked 17 Times in 14 Posts	Gentlemen, Thanks for the responses. As Ed suggests, repair of major pitting is never likely to be a cost effective undertaking. I do it (rarely) because I enjoy it and can, if I have the time and really want to. My primitive method has been to bead blast and then overlap a series of weld beads using 1/16" rod at about 50 to 55 amps with a conventional arc welder. All "hits" are less than one second, so good visibility and an instant auto-darkening helmet lense are essential; can't be done any other way. But this is very demanding and difficult. And then you have to do some delicate machining and/or grinding to get back to a level surface. TIG would be much better, but I don't have that gear. On rounded surfaces, it's tough, unless you can mount the weld-filled piece in a metal lathe and turn it back down. So it can be done with barrels. I did it with one of my Thompson barrels years ago...a barrel which a professional gunsmith had badly carved up with a hacksaw, besides the pitting, because that was the easiest thing to do when removing it, and he didn't think the barrel was worth much; "then", that is. The easiest part of the whole job is putting on the blue or parkerizing; so far, I've always gotten a perfectly blended match, as long as there is no nickel or chromium in the original gun alloy or the welding rod used for filler. If you use the wrong rod, no way will you match it, although you can cover it over nicely with one of the modern spray-on finishes...but not on a Luger. Guys, have I learned a lot after a few hours of Internet research yesterday. There is a much better and easier way to do all this if you have access to certain modern technology, which is rather widely distributed. There is a process called "arc thermal spraying", and there are about three other closely related processes. All involve using clean dry air, or an inert gas, to blow liquified droplets of metal onto your pitted surface, which has been sand or bead blasted and made very clean. Before solidifying, the droplets flatten and overlap. You have perfectly fused new metal, much like welding, if you did it right. One of the best part is that the substrate, your gun or gun parts, get barely any heat. They are not warped or distorted. And because of the lack of a heat threat, you can use certain masking tapes to mask off your pitted area, as though you were spray painting; which is exactly what is being done. Some versions of the equipment dispense powdered metal and others use two wire-feed electrodes which arc, to produce the droplets. All versions do the same thing, build up your surface with newly fused metal droplets. Much of the equipment consists of small, very portable components; it's intended for field use on damaged equipment or parts. I think most of it looks too expensive for basement hobbyist use, but quite a number of small repair companies have it and advertise that you can send them your gear for repair, at reasonable cost. I would imagine that could include gun parts. I expect that in most urban areas somebody has this stuff. Almost any metal works. It is being done with steel, brass, aluminum, and a variety of alloys including monel and even carbide, for restoring large cutting tools and such things as scraper blades and industrial teeth of various types. Sounds to me like some miraculous fun technology, and I thought some of you might like to know. People are offering these services all over the net. Do a search on "arc thermal spraying". Oh, yes, sorry I did not save the url, but the U.S. Navy is into this in a big way, for repair of everything under the sun on ships, from small stuff to hulls. On the net, I found publication of the Navy's wonderful overview training manual for explaining to new maintenance trainees what main technologies are out there (four, I believe), how they work, and very precisely how you do it yourself...and what to avoid. For those of you who are incurable restorers, as I am, I hope you enjoy looking into this on the net. It's something to keep in mind, next time you have a worthwhile collector firearm which may be in pretty good general condition, except for a very localized area of deep pitting damage; send it out for a minor skin graft. What would be really neat is if there were a version of this sprayer small enough to use like an air brush. Maybe there is. The ones I saw were about the size of a gun you would use for spray painting a car.