Silver Soldering 101 - Soldering in General

Discussion in 'Gunsmithing and Repairs' started by Johnm1, Jan 15, 2022 at 1:53 AM.

  1. Johnm1

    Johnm1 Member

    Feb 24, 2008
    Mesa, AZ
    In a thread in the black powder forum I mentioned that I need to learn how to silver solder. I managed to accomplish it once a couple months ago but it took me 8 tries and I really don't know why that attempt worked and the other 7 attempts failed. I'm hoping @SC45-70 will chime in. First things first. I did manage to silver solder 2 pieces of 0.062" brass plates together to make a 0.124" replacement front sight for an 1860 Army I've been working on for a couple of years.


    That was uneventful. Cleaned both pieces in acetone and put flux between the plates. Heated the plates until the solder melted due to the heat of the brass.


    Filed the plate to clean up the surfaces and fit into the slot on the end of the barrel and soft soldered it in place (I need to remove it for the final polish). But the soft solder didn't go as smoothly. I didn't pull the flame away from the work when I tested the solder to see if it was hot enough and must have gotten the flame too close and I melted the solder with the flame. I had a mess to clean up.

    The gun shot wildly high with the nub of a front sight that was on the firearm when I bought it. I'm going to file it down to shoot point of aim at 25 yards with a 20 grain powder charge for round ball and see where 18 grains with a conical ends up.



    Enough about the specific task, this thread is about learning how to silver solder.

    At SC45-70's suggestion I purchased Harris Safety Silv 45. I was unable to locate the recommended Aircosil flux but bought a combination of the Harris Safety Silv 45 and the Sta-Silv flux that came in the package. I have other silver solder I bought at the hardware store but it doesn't disclose the silver content. I also have soft solder if learning is easier with it. I have lots of old steel gun parts and varying thicknesses of brass plate to practice on. I have a standard propane torch as well as an Oxy/MAPP gas torch.

    What are some good exercises to practice/learn on?

    Also, the flux that came with the Harris Safety Silv 45 is dry and not 'paste like' as I expected. It can't be applied with a brush. Is it suppossd to be thin enough to apply with a brush? If so, can I thin it and with what?

    I'm hoping @BBBBill , @Michael Tinker Pearce , @Jim Watson and anybody else who can solder will chime in.
    Last edited: Jan 15, 2022 at 1:59 AM
    SC45-70 likes this.
  2. SC45-70

    SC45-70 Member

    Aug 24, 2013
    The first thing I do when soldering is to clean the metal on a belt sander, then use acetone. The metal must be clean!
    On something small like a sight I use silver solder ribbon. If you don't have ribbon silver solder you can pound your solder flat on an anvil.
    Pound it as flat as possible as the thinner it is the easier it will melt.
    I use past flux and flux the metal generously. The flux I use is water solvable, if it dries out I just add water. Try a small amount of your flux and see if it will mix with water. If not you may have to melt the flux on the metal before adding the solder.
    On Small items, use the smallest hottest flame that you can get with your torch. A trick I use when using a small flame is to light a small propane torch and keep it burning so that I can use it to quickly relight my brazing torch in the event the flame goes out.

    On small objects sometimes it helps to cut a small piece of solder and lay it on the fluxed metal and heat from the opposite side. If soldering 2 pieces of flat thin metal together place a piece of ribbon solder between the pieces before clamping together.

    Use the smallest clamps possible and keep them as far as possible form the joint as they act as heat sinks.

    Clean the metal!
    Use flux and don,t burn the flux.
    Practice, Practice Practice.
    Silver soldering is a learned skill.
    I hope this helps, you can message me with questions.

    Last edited: Jan 15, 2022 at 9:53 AM
    Johnm1, usaral63 and Armored farmer like this.
  3. Blue68f100

    Blue68f100 Member

    May 25, 2011
    Piney Woods of East Texas
    Remember the solder will be drawn to the heat. Like in plumbing, you only need to heat on 1 side and apply the solder on the opposite side. Learning how much heat is required is the hardest part to learn. There are many alloys used in silver solder, some melt at real low temp while others very hot.
    Johnm1 likes this.
  4. Kp321

    Kp321 Member

    Jul 12, 2012
    West Texas
    One of the big problems with high temperature silver soldering (silver brazing) is not using enough heat. A propane torch is marginal for thin metal but not enough heat for thicker sections. A small torch will eventually get the metal up to temperature but the flux is burning away and the metal is oxidizing all the while. An oxy-acetylene torch will bring the metal up to temperature quickly and can be set to produce a slightly reducing flame which will reduce oxidizing. Clean metal, good fluxing, and sufficient heat are the secrets.
  5. BBBBill

    BBBBill Member

    Mar 7, 2005
    Alabama and Florida
    I'm a hack at soldering. I've had some limited success with Brownell's Hi Force 44 which is a low-mid temp silver solder. I've used that to solder sights on revolvers several time and none have come off and also did a shim on a worn break open, but it's been a very long time since I did any. Got called away to active duty immediately after 9-11 and finally retired in 2014. Had a bunch of surgeries just proir to retirement and it took a long time to recover, so I'm wading back in slowly. I went around to local pawn shops recently looking for old cheap shotguns specifically to practice repairs on including soldering. I had worked on mostly 1911s, S&W and Ruger revolvers, and FN/Browning Hi Powers previously, so not abunch of experience with shotguns where soldering skills would come into use more often.
    Johnm1 likes this.
  6. .38 Special

    .38 Special Member

    Sep 15, 2006
    The Safety-silv is good stuff. The flux that comes with it isn't great, but works. I really like Gasflux type "U". Regardless, it should be a paste. Add hot water and pulverize it with something blunt like a screwdriver handle. If you have the time, let it sit for a day, and then stir it into a paste. Otherwise it will be lumpy, which still works but isn't perfect. As an aside, there really is no such thing as too much flux, and I suggest liberally coating all surfaces, outside and in.

    Heat is actually your enemy, when silver brazing. The underlying metal needs to be ridiculously clean, and too much heat causes oxidation, which ruins the joint. You'll want to watch the flux: it will turn "glassy" when the temperature is right, and that's when you want to feed in the silver. If everything is perfect, the silver will "zoom" through the joint, and you are done. Continuing to add heat just makes things worse, and especially with small workpieces, propane and oxy/Mapp are plenty.

    The single most important factor is cleanliness. The metal has to be completely free of oil, oxidation, and any other contaminants. I like to soak the workpiece in a hydrochloric acid solution (conveniently sold as toilet cleaners like "The Works") then rinse with water and immediately coat with flux. Then bring the piece up to temperature so that the flux turns glassy, add in the silver, let it cool naturally, and then soak off the flux in hot water. Easy, after the first hundred tries!

    <edit> Brazing together two bits of brass shouldn't be a huge trick. Brazing together two bits of silver brazed brass onto a gun barrel is actually pretty hard. The trouble, as the OP has found, is that by the time the big piece of steel is hot enough, the little bits of brass are glowing orange and smoking. I personally would coat the barrel in flux, heat it until the flux is glassy, and then introduce the brass blade. This should allow the blade to quickly come up to temperature, and then some of the extra silver on the blade should flow onto the barrel. If there is not enough silver on the blade, the barrel can be "tinned" beforehand. The whole process still requires three or four hands, of course...
    Last edited: Jan 16, 2022 at 1:41 AM
    beag_nut and Johnm1 like this.
  7. Johnm1

    Johnm1 Member

    Feb 24, 2008
    Mesa, AZ
    This is great information. Thank you all for taking the time to relay your experiences.

    As far as practice goes, it looks like I'll be practicing using low temperature non silver solder and propane for a little while. I ran out of MAPP gas but there appears to be a run on it and the oxygen bottles as well. Heck, even propane was sold out. At least I have some propane.
    .38 Special likes this.
  8. doubleh

    doubleh Member

    Feb 14, 2007
    NM-south of I-40
    Don't feel bad about your experience. I made my living as an ASME Code 9-G6 certified welder for many years. Soft soldering is easy, brazing with an A/O torch is easy. For some reason I never managed to get the hang of silver soldering down very well. Oh. I made it work but the job always needed a lot of cleanup to look alright. I can remember only one decent silver solder job. I made a ramp front sight for a shotgun with a piece of 14 ga. plate and a BB and it worked great. Other than that one, not so hot.
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