Soldering steel

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Main Question or Discussion Point

... Shotgun top rib back on to barrels. I’ve sanded it bright, degreased and fluxed with RMA flux. The 50/50 tin/lead solder just won’t run into the joint, no matter how hot I get the steel.

Any tips before I spot weld it?
 

Answers and Replies

  • #2
berkeman
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Do you think the barrel will still be straight after all of that?
 
  • #3
Bystander
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Do you think the barrel will still be straight after all of that?
*Barrels - this is not a rifle. According to my research, this is how the ribs are traditionally soldered in place.
 
  • #5
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Don't spot weld. Before joining the pieces together their surfaces ought to be tinned. Haven't watched any but this one, but Jack Rowe seems to know what he's talking about.

 
  • #6
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Don't spot weld. Before joining the pieces together their surfaces ought to be tinned. Haven't watched any but this one, but Jack Rowe seems to know what he's talking about.

I’ve seen that one - even Jack Rowe, my fellow countryman, sends them off to be re-soldered. Concensus on another forum is to use 5% silver 95% tin and acid flux. Spot welding always on the horizon, but this is a nice old hammer gun from the early 20th century - it would break my heart to use such an ugly (but effective) method.
 
  • #7
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I'd experiment around with pieces of steel scrap with different solder compositions and fluxes. I don't know what RMA flux is (an organic rosin, perhaps) but for the few steel things I've soldered acid flux was my choice.
 
  • #8
Tom.G
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Acid flux is key here. RMA stands for Rosin Mildly Activated and is used in electronic assembly, etc. where corrosion is to be avoided and thorough washing/cleaning is not applicable. Be sure to clean off all flux residue after soldering, it is rather corrosive.

Silver Solder is recommended as it is harder than ordinary Tin/Lead (Sn/Pb) and make a stronger bond; it does have a somewhat higher melting point though, and it is a little more viscous, which makes for a bit of a learning curve if you are used to Sn/Pb soldering.

One of the biggest problems to soldering to a massive piece of metal is to get and keep the work area hot enough to melt the solder. I've seen people trying to use a 35 Watt solder iron on a large part and wonder why they can't solder. At the other extreme I've seen people trying to use a Propane torch and wondering why the solder won't stick (they heat the work OK but then decompose the solder by applying the solder into the torch flame.)

Often the whole workpiece is pre-heated in an oven to minimize the heatsink effect tending to cool the work area.

To get solder to bond to ferrous metals especially, frequently some mechanical scrubbing of the solder iron is needed to scrub any remaining oxide from the metal surface. If the solder melts but beads up rather than flows on the work, use a little abrasion to get the solder thru the remaining oxide film.

Tinning the work first makes soldering easier, however for your usage you need straight/flat surfaces so some extra work is needed. After the surface is tinned you will need to re-melt the solder and wipe off the excess to get a smooth surface so the parts mate well. A piece of Burlap seems to work, fiberglass mat could be a cleaner alternative but I haven't tried it.

As usual when soldering, make sure there is no movement of the parts until the solder has solidified. A mechanical disturbance causes the solder to flash solidify to a chrystalline phase that is very weak.

After all of that, I realized that gun ribs are typically brazed these days rather than soldered. Brazing is similiar to soldering but at higher temperatures and usually uses a copper-based filler instead of Sn/Pb.
See: https://www.google.com/search?&q=brazing+vs+soldering

Have Fun!
Sounds like an interesting project.

Cheers,
Tom
 
  • #9
Averagesupernova
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I have never had trouble soldering mild steel. The steel that is in a gun barrel might be different though. Have you tried muriatic acid as a cleaner first?
 
  • #10
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Many thanks for the replies, particularly @Tom.G ‘s detailed response. They’ve given me a few things to try:
1. Acid cleaner - the blueing may be interfering with the bond.
2. Acid flux - since the barrels will be together after the job, I didn’t want anything too corrosive to be left between them, as it can’t be flushed out. But if that’s what’s needed...
3. Silver solder.

I do my own plumbing, and have never had a problem with copper joints - clean, flux, heat the solder with the metal, not the torch. I’ll update if I crack the problem :wink:
 
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  • #12
jrmichler
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Shotgun top rib back on to barrels.
The book Gunsmithing by Roy Dunlap has a whole chapter on soldering and brazing. It's still in print and available from Amazon. Highly recommended. Bob Brownell's Gunsmith Kinks (1969 edition) has a couple of pages about soldering and silver soldering. That book is also still in print and available from Amazon. I'm sure there are other books that cover the subject, these are just the ones that I have.
 
  • #13
jim hardy
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I've soldered steel before with 60/40. As with copper cleanliness is key. Absolutely you have to remove the blueing down to shiny steel.
I find Mapp gas doesn't work well it does something to the solder and it won't stick. I prefer propane.

I've had good luck with this silly little trick -
place a single grain of copper sulfate in the center of the area you've cleaned.
Add a drop of distilled water.
After a few minutes a tiny amount of copper will plate out onto the steel if it's clean. All you see is a hint of copper color.
Rinse, flux and solder. The few atoms of copper help immensely. i even get away with rosin flux. .

Copper sulfate is a blue crystal that comes in a one pound pail at my local farm supply store. That's a lifetime supply for me and several generations of descendants. A jeweler might be able to provide you with a few individual crystals.

old jim
 
  • #14
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I've soldered steel before with 60/40. As with copper cleanliness is key. Absolutely you have to remove the blueing down to shiny steel.
I find Mapp gas doesn't work well it does something to the solder and it won't stick. I prefer propane.

I've had good luck with this silly little trick -
place a single grain of copper sulfate in the center of the area you've cleaned.
Add a drop of distilled water.
After a few minutes a tiny amount of copper will plate out onto the steel if it's clean. All you see is a hint of copper color.
Rinse, flux and solder. The few atoms of copper help immensely. i even get away with rosin flux. .

Copper sulfate is a blue crystal that comes in a one pound pail at my local farm supply store. That's a lifetime supply for me and several generations of descendants. A jeweler might be able to provide you with a few individual crystals.

old jim
Thanks Jim - what an interesting trick!
 
  • #15
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Tom G hints at one of the most common issues I see. Solder will flow from a place of low temperature to a place of high temp. It will not however flow when it is not liquid. To get an effective solder joint make sure the base metal is fully up to temp. When one accepts the temptation to melt the solder with the flame it will not flow. The base metal is what cools it below the creep point where it enters the joint. Make sure your joint is up to temp first and bias the heat to the highest sink side. Rest the solder on the base, in the flux, away from the flame. When the temp is right it should flow in. Your flame should be away from the solder at the time it is applied. The solder will flow from the cold side (Where it is just barely warm enough to melt it) towards the warmer side of the joint.
Oh and +1 on the blueing. Make sure you are stripped clean to base metal at the joint and surrounding area.
 

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