Soft solder and flux for steel

[HighUintas]

I've got some 60/40 rosin core solder on my bench. From what I can find on the forum through searching, it sounds like this should work fine and be plenty strong for underlugs, sights, and ribs and tinning both parts prior seems to work best.

For flux, I've seen a lot of guys mention acid flux, but there is the issue of the need to thoroughly clean to prevent bad rust.

Would would regular paste flux work just as well instead? I do not know what kind of flux that is or what brand. I haven't been to the hardware store to look through the options yet.

Also, I have Solder-It paste, which is the low melt point, high strength silver solder that initially melts around 400 and remelts at 650ish. Would this solder be problematic for using to attach a sight base on the barrel if I want to remove it later? I only have a hand held propane torch with the currently available yellow "map" gas bottle. I don't know if I could actually get the barrel hot enough to remelt that solder paste.

[Daryl]

Certainly the Mapp Gas will and the Mapp Gas nozzle on a propane bottle will also work as the temp is increased radically with the addition of the extra oxygen the Mapp Gas nozzle sucks in.

[rich pierce]

For underlugs almost any solder will work. It’s just holding thin wood up to the barrel. I wash the area with soap and don’t get after-rust. If I forget and just wipe it down, it will definitely rust with acid flux. Every time.

[P.W.Berkuta]

You state that you have "60/40 rosin core solder" and want to use it for soldering barrel tenons on to a steel barrel. Well - rosin core solder is for soldering brass and copper not steel. The flux will not "wet out" and prep the surface properly to join the steel surfaces for that you need an acid flux and yes you MUST neutralize the flux to prevent rusting. I use Stay-Brite solder, and its flux Stay-Brite paste flux - the liquid flows all over and is not as controllable as the paste.

[B.Habermehl]

I use lead free plumbing solder, and regular paste flux from the plumbing isle in the local hardware store. Absolute cleanliness is imperative. Freshly sanded steel surface or filed. No fingerprints etc. I usually flux one part and tin the part with solder. Then flux the other part and clamp together. Heat just till the solder flows. It will flow twards the heat. If you overheat you will burn the flux, then it’s start over time. Not difficult. BJH

[Scota4570]

My procedure goes like this.  Clean the area to bright clean steel.  This is vitally important.  I use lead tin solder for electrical soldering.  The exact percentages do not matter.  I tin both areas with acid paste they sell for plumbing.  The metal is heated and the solder applied with a little ball of steel wool held in pliers.  The steel wool has the flux and solder on it.  The solder will rub on the metal like paint.  Do not heat the metal more than necessary to melt the solder.  IF you get heat colors start over.   After tinning the whole surface will be bright silver.  Then wash off all the flux. I then paint on liquid rosin flux marketed for electrical work.  Rosin is not corrosive.   Then jig it up as needed.  Gently heat both parts.  When the solder melts I feed in rosin core solder to fully fill the joint.  Let cool, clean up, done.

I the majority of the trouble I read about is from over heating and expecting to be able to make a good joint without tinning it first.  IT is a two step procedure to make sure it is 100%.  Miracle pastes and gimmicks have not worked for me. Jigging the parts and feeding in flux and solder may or may not work.

[HighUintas]

You state that you have "60/40 rosin core solder" and want to use it for soldering barrel tenons on to a steel barrel. Well - rosin core solder is for soldering brass and copper not steel. The flux will not "wet out" and prep the surface properly to join the steel surfaces for that you need an acid flux and yes you MUST neutralize the flux to prevent rusting. I use Stay-Brite solder, and its flux Stay-Brite paste flux - the liquid flows all over and is not as controllable as the paste.

This is is interesting. So even if I use acid flux or a paste flux on the surface after prepping it, will I not be able to properly tin the surface with the rosin core solder even if I use Scotas steel wool ball method?

Is there something about the rosin that interferes with it? Or are you saying that using the rosin core solder alone, without using additional flux, wouldn't work? The latter makes sense because there is so little flux in there.

[Scota4570]

You state that you have "60/40 rosin core solder" and want to use it for soldering barrel tenons on to a steel barrel. Well - rosin core solder is for soldering brass and copper not steel. The flux will not "wet out" and prep the surface properly to join the steel surfaces for that you need an acid flux and yes you MUST neutralize the flux to prevent rusting. I use Stay-Brite solder, and its flux Stay-Brite paste flux - the liquid flows all over and is not as controllable as the paste.

This is is interesting. So even if I use acid flux or a paste flux on the surface after prepping it, will I not be able to properly tin the surface with the rosin core solder even if I use Scotas steel wool ball method?

Is there something about the rosin that interferes with it? Or are you saying that using the rosin core solder alone, without using additional flux, wouldn't work? The latter makes sense because there is so little flux in there.

It is fully tinned using what I described.  In my experience the rosin will be plenty to keep the solder from oxidizing and if flows nicely. Rosin is used and was historically used as solder flux.  I have also used it with the steel wool method.  It is a little more fickle.   

I have read about joining double barrel shotgun barrels.  I am pretty sure I described that way above.  You would not want acid flux between the barrels and under the rib.  It will rust over time and that would ruin the job.

 ........found an example: 

https://www.vintageguns.co.uk/magazine/soldering-on

[sdilts]

I've been using Solder-It paste for a long time. I just soldered on a rib and thimbles today with it. A propane torch is all you need. It will get hot enough to remelt if need be.

[HighUintas]

I've been using Solder-It paste for a long time. I just soldered on a rib and thimbles today with it. A propane torch is all you need. It will get hot enough to remelt if need be.

A whole rib? That is impressive given the small tube. How much of the tube did it use?

[Stoner creek]

Another vote for the paste solder!

[sdilts]

A whole rib? That is impressive given the small tube. How much of the tube did it use?
[/quote]

It doesn't take as much as you think, maybe a quarter of the tube, never really paid much attention.

[P.W.Berkuta]

You state that you have "60/40 rosin core solder" and want to use it for soldering barrel tenons on to a steel barrel. Well - rosin core solder is for soldering brass and copper not steel. The flux will not "wet out" and prep the surface properly to join the steel surfaces for that you need an acid flux and yes you MUST neutralize the flux to prevent rusting. I use Stay-Brite solder, and its flux Stay-Brite paste flux - the liquid flows all over and is not as controllable as the paste.

This is is interesting. So even if I use acid flux or a paste flux on the surface after prepping it, will I not be able to properly tin the surface with the rosin core solder even if I use Scotas steel wool ball method?
I have never used rosin core solder on steel only brass or copper so I can't give you an honest answer - sounds like Scota 45-70 has done this so go with his method and see how it does? The steel wool keeps the surface clean along with the flux so that the solder can "bite" and clean the metals surface. The tinning prevents oxidation so that the solder can join the two parts together.

Is there something about the rosin that interferes with it? Or are you saying that using the rosin core solder alone, without using additional flux, wouldn't work? The latter makes sense because there is so little flux in there.

[Steeltrap]

Yup....the entire length of the underbid with soft solder, along with the RR pipes. This pic is the initial "finish". I re-applied soft solder to the gaps, then cleaned that up for the finish. It's all holding up very well. To my surprise.....but I did follow the advice given here. The soft stuff works great for this. I couldn't imagine the heat needed for SS to work.

[Daryl]

Seems to me  the rib should be one with the bottom flat, not raised on solder clumps. Perhaps it's just the picture when I enlarge it.

[Steeltrap]

Seems to me  the rib should be one with the bottom flat, not raised on solder clumps. Perhaps it's just the picture when I enlarge it.

Yes. Initially it was. Since this was my first attempt at an under rib, the first attempt looked like that. Then, using spaced apart C clamps I applied heat (and solder where needed) and compressed the rib into the barrel.

I found another pic that shows "a better" job of soldering it on. Now, is it  perfect? No. Could I have done better? Likely if I kept at it. But I got it to "acceptable for me" and that's how it stayed.

When I initially planed on doing a half stock, I read several post on the forum. IIRC, the majority stated they would rather do a full stock than a half stock. I thought....Nah...that can't be right. Well....it is. I'd rather build a full stock than a half stock after this experience.

[Leatherbark]

For a regular octagon rifle barrel, I find it much easier to use screws to attach a rib. The solder the thimbles on with regular plumber's solder.  I have found that round barrels seem easier to solder the rib on than an octagon flat.

Bob

[smylee grouch]

When soldering ribs on I have found it helpful once the metal , rib and barrel are preped, clean and tinned to heat up a 3\8 inch brass rod and place in the bore. Seems like it takes less time to heat up the barrel rib unit when that time comes.

[Scota4570]

I solder all my ribs.  Once tinned, jigged, wired, clamped, etc. it is easy to work my way along heating it as I go and flowing in solder a little extra solder.  There is no need to heat it all at once.  I also solder the thimbles at the same time.  Normally I have no visible solder after clean up. 

[kutter]

Acid soldering flux is Zinc Chloride.
It's acidic on the PH scale, but not really an acid
But it will rust very aggressively if not cleared completely from the surfaces after the soldering job is done.

You can make your own by disolving Zinc in Muriatic Acid (Hydrochloric)
Keep adding Zinc till it won't disolve any more of it. Let it set and settle then strain it off into a bottle.

Zinc from (old fashioned?) flashlite batterys, the cup that the batter case is made of is Zinc.
The black powder inside is Manganese Dioxide. That's usefull to add to Nitre Salts to lower the melting point.

Or just splurge and buy some Acid Flux. It does work great, but that after rust issue must be dealt with.

The Paste Flux often has Zinc Chloride in it. So wash the surfaces clear of that as well or they may rust on you

Easy on the heat, don't over heat. Tin at least one surface,,both of you can.
Then flux the mating surfaces again, clamp together and reheat till the solder flows. Tweak the clamp tighter at that point just a little.

The 'Silver Solder' around is still 'soft solder' It's just a Tin/Silver alloy usually 95/5.
But there are variations of that. It's strong, solders easily as lead/tin solder in my experience.
But I stillprefer the50/50 or 60/40 Lead-Tin soft solder as any of it that shows as a soldering joint line will Oxidize pretty quickly and turn a dark grey color.
The Tin/Silver soft solder stays Brite White . A fine silver bright line running up and down a soldered rib to bbl doesn't look very nice no matter how thin it is.

I've done a lot of relaying ribs on SxS's and use Lead/Tin solder.
Plenty strong if you have a good fit betw parts. Don't ask it or any solder to be a crack filler. No strength in that capacity.

Once you have clamped the tinned and fluxed parts together and before heating them, take a soft 'lead' pencil and scribble the metal around the parts. Cover the surfaces with pencil marking. That will be a graphite coating and any excess solder will not attach itself to those surfaces.
Easy cleanup

[P.W.Berkuta]

I silver braze on the ram rod tubes then I tin the rib's underside. I will tin the barrel also and then lay the rib in place. Hold it down with baling /fencing wire flux the first 4 " and start to heat and apply solder if needed. I move back another 4"and keep doing this until all of the rib is soldered down in place. when cooled I clean up any excess solder with a cheap plastic handled wood chisel and file. This will leave a very faint soldered line that is barely noticeable.

[HighUintas]

I tried Oatey solder paste last night because the hardware store didn't have Solder-It and I'm out. I also got some regular ZnCl flux to use with the 60/40 solder I have, but wanted to try the Oatey solder paste.

The SDS for it says Tn (40-70%), Cu (1-5%), and Bi (0.5-1.5%) and it uses ZnCl as the flux. Melt temp is the 450F range. I'd assume it may not be quite as strong as soft solder with a bit of Ag in it, but I would think it would work fine for most uses like underlugs.

I made an underlug and it seemed to work fine but left a very uneven, bubbled and cratered looking surface. I still need to clean up the bottom of this lug to thin the base to 0.032.

I do not know how to test the strength of this paste solder.

https://ibb.co/jk0XQPP8

https://ibb.co/HpdYkgwT

[Daryl]

The bubbly is probably due to the "amount /quantity" of ACTUAL solder in the volume of paste used.
I recall this from using it back in the 70's. It appears to be quite similar to what I attempted to use. I
went back to using (high temp) silver solder as well as silver bearing low temp and 50/50 solders.