Tell me about "Sweat-soldering"...?

[AJMD429]

I have a one-piece scope-base that is radiused to match the .45 Colt magazine tube on my Rossi, and rather than do the 'conduit mount' like on my Marlin 'Night Scout', on this one, I'd just like to solder the durned thing right on there. I figure they do it with front sights, so I don't see why it shouldn't work. I assume I'll have to do some re-bluing after.

However, I have a few questions:

• 1. How is 'sweat' soldering any different than 'regular' soldering (like you'd do with copper plumbing pipe)...?
  
  2. (Unimportant, but curious - ) Why do they call it 'sweating' anyway...?
  
  3. Can one sweat aluminum to steel...?
  
  4. What kind of solder should be used; I've accumulated several kinds over the years:
  
  • a) plain
    b) lead-free
    c) 60/40
    d) rosin-core
    e) acid-core
  5. What kind of 'flux' should be used...?
  
  6. How thoroughly does the bluing have to be removed before soldering...?
  
  7. Would it be all that 'inferior' to just use JB-Weld...?

[J Miller]

I'll be watching this thread. I've asked most of those questions myself.

Joe

[Washita]

I've never done it, but I'm pretty sure "sweating" is silver-soldering, and the resulting joint is much stronger than any soft soldered one. I think it's done just like brazing, except the solder is silver. Beyond that, anything I said would be guesswork.

[Ben_Rumson]

JB weld or some good epoxy would be the way to go..
“Sweating” is when capillary attraction draws the solder into the joint.. Say you have a lap joint ... Heat is applied along the joint until the solder flows... If you were to direct the heat back farther on the work piece away from the lap, but the joint was still at soldering temp, then the solder being applied at the joint would "sweat" back farther between the two pieces being joined...
Traditional lead based solders and silver solders wont join aluminum to iron based metals...Last I checked any of the fluxes and rosin or acid core solders will remove or ruin bluing practically instantly, so you really need to mask or contaminate the area or build dams near the work zone so the solder flux doesn’t run out on to areas you don’t want the bluing ruined on ... Pencil lead rubbed on the area will help keep the solder from running out where you don’t want it. Commercial masking agents are available to prevent this. So, mechanically remove the bluing where you want the solder .. Mask the area you don’t want it..

[claybob86]

I would not trust JB or epoxy for such an application due to the shock and vibration, as well as oil and solvent contamination.

[gundownunder]

Sounds to me like a good way to damage a barrel if you aren't really careful about how much heat you apply.

[AJMD429]

Sounds to me like a good way to damage a barrel if you aren't really careful about how much heat you apply.

Yep. Aluminum (the scope mount) also melts pretty fast, too, something in the 500-700 degree range.

I think I'll just use JB-Weld...

[milton]

I don't know if you want to go to the expense but a Methacrylate glue- MA920 is very good for what you are doing. The dispenser is the expensive part and the glue has a relatively short shelf life.I have used it to widen the front sight on a single action and to mount the flash hider on a No. 5 Enfield and the stuff is TOUGH !.The stuff is used in industry to "spot weld " fuel tanks in cars.Just Google MA920 and take a look at the characteristics of the set glue.

[Cliff]

Sweat Soldering is a learned craft. Someone who can do it will do great job. But don't try steel to aluminum and such. Go with the epoxies or glues. Heck the space shuttle and high tech. fighter aircraft are pretty much glued together. I have glued sights on several bubbaed up surplus military rifles people brought to me using epoxies. Couldn't breat the sight off using a big hammer, also I know of several still going strong 30 years later. The new stuff today is really great if you follow their directions to the letter, clean up is easy and in some cases it isn't to hard to undo. Good Luck.

[Leverdude]

Sweating is just like someone already said. Once brought up to temp the solder will suck in thru capilary action. It can be done with any type of solder. Usually things on guns are silver soldered. I think honestly (though I'v never soldered a gun part on) you would be better off to tin both parts ahead of time. Tinning is applying solder to the pieces to be joined on the mateing surfaces. You would want to clamp the mount in position so you could scribe a line around it. Then degrease & remove the finish from the are to be tinned. Once the parts are tinned you put them together and bring it back up to temperature & if everything is right in the world it'll stick. Aluminum melts at much higher than 700 degrees and can be soldered, though I'v never been sucessful at it the book says you can do it. I'v got solder to stick to it but never got a decent solder joint. I'm a coppersmith by trade (or was before the economy crapped out) and do an aweful lot of soldering sheet stock, mostly copper but also galvanized or stainless on occasion.
Aluminum I'v tried because they say you can & sometimes the architect specs it. But its easier to have a friend weld it if I cant talk the builder out of it entirely. From what I understand the issue with aluminum is it oxidizes very fast leaving almost no window after fluxing to get a nice flow. The solder mostly just beads up on it.

Anyway I'd let my smith do it, theres just too much can go wrong.

[Chuck 100 yd]

You can not soft solder aluminum to steel or to anything. Use steel to steel if you want it to work out. Brownells force 44 solder is a silver bearing solder that melts at low temp and has a strength of around 30,000 lb. sq.in. Brownells also sells a silver solder that is ground up silver solder mixed with the flux. You just clean the joint,paint the solution on the surface of one part,clamp and heat. the parts will fuse together and is the strongest joint possible short of welding.

You can use chalk to keep the solder from running onto areas that you don't want the solder to go. A very thin line around the joint to almost no bluing will need to be disrupted if done right.

Call and ask Brownells for the instruction sheets for Force 44 and for their silver solders and read. They will; send them for free, just for the asking.

[AJMD429]

I just decided to use J-B Weld - I'll post pics when it's done...