hard versus soft solder

Hi, Mike. Looks like you have all the correct answers, already.

The rosin core solder is really meant for electrical/electronic assembly. Electronic components normally are coated with a thin solder coat during manufacture, so when the user solders, the flux doesn't have much work to do in cleaning the work.

I think you are wanting to solder brass that does not have a solder coating. In this case, the flux has a really hard job of cleaning all the surface of the brass. Oil from your hands, dust in the air, cooking fumes and who knows what else, have put a very thin layer of contanimation on your brass. The flux you use will have to dissolve this contanimation and move it away from the solder, as you apply heat. Solder will not adhere to the brass where any contanimation is living.

I think you need to find some acid core solder. When this is heated, the flux decomposes into an acid that eats away the contanimation layer and lets the solder make contact with the freshly exposed brass surface. This type of solder used to be available in hardware plumbing sections. Plumbing now is forced to use lead-free solder, so I don't know if the flux is still acid or not. The lead-free solder will also work for your "hard solder" needs.

In all cases, be prepared to wash your project with hot soap and water and then rinse will. Any acid flux left on the brass will still be active and will eventually turn the brass to a green color.

Are you using a soldering iron to make the joints for your project? The hard solder will require a higher temperature than lead/tin solder. Perhaps 40-50 degrees hotter. Depends on the solder. Your iron may not be up to the job if it is designed for lead/tin solder.

Good luck > I'm doing some brass model building and the book that I am using as a

[Both the types Paul mentions in his reply below are actually variants of soft solder, although one melts slightly above the other. While these can work on brass to some extent, the joints will be weaker than those made with hard solder. The melting points of these soft solders are all well under 800F, although there are intermediate types that will require hotter temperatures. True hard solder is much different; it's also called silver solder, (not to be confused with "silver bearing" solder which contains a small amount of silver) and melts at temperatures ranging from ~1240 - 1365F although the flow points are somewhat higher. Real silver solder is mostly silver, and it's used by jewelers to make invisible joints in silver rings, etc. (They also use gold solder, which is similar but based on gold instead). Silver solder will work with brass, steel, copper and some (but not all) other metals. It's too hot to melt with a soldering iron; you need a torch to use it effectively. It's also important to have everything clean, and to make the joints fit closely without any gaps, which this type of solder won't fill. Use white paste flux (a different type than for soft soldering) Handi-flux is one popular brand; your local welding store will usually have some flux that will work - ask for "silver brazing" flux. To get silver solder, look for a jeweler's supply company like Rio Grande, Indian Jeweler's Supply, Alpha supply, etc.]

Andrew Werby

Hi Paul, I should have mentioned the tools...

For the most part, I am using a butane soldering torch. This one from Micromark is pretty close to mine:

I also have a mini torch that fits on the end of a propane bottle. I don't use that one much because the butane one is a lot handier with the auto light feature.

For whatever it is worth, I am using flux with the rosin core solder.

So..if I am reading this right, the solder that plumbers use for soldering copper pipe is a "hard" solder, correct? Interesting. I more pictured those sticks of silver solder as a hard solder.

Once I solder something with a "hard" solder, can I go back and add a part by "soft" soldering it without the previous part coming loose since I should use less heat with soft solder?

Take a look at my website for what I have gotten done so far on my first model. Click on the pic of the mini-lathe on the homepage and then the trailer on the next page:

Mike

Hi Andrew, I know what you are talking about for the silver solder. I used to get this stuff for my dad at his radiator repair shop (many years ago). It came in strips something like 6" long, 1/8" wide and maybe 1/16" or so thick. Will my little butane torch melt this stuff? What about my propane mini-torch? Or is this something for an O-X setup?

I am building the hitch for my model trailer. It is going to be about

10 pieces in the area of the size of a quarter. I tried milling this out of a solid chunk of brass, but my experience level is not up to that task. Too many cuts and angles. I am now going to try to mill the main pieces out of flat brass and then silver solder the main pieces together (four pieces). I will then use a soft solder as mentioned for the detail pieces. If I get some time tonite, I'll post a picture of the hitch on my website.

Strength is not an issue as this will be a static display model.

Thanks for all the advice so far!

Mike

The jewelers are the kings of solder, and that is where I have heard a lot of references to hard and soft solder. They will use different temperature solder to assemble complex pieces. They start with the higher temperature solder, and finish with the lower temperature solder. This reduces the risk that soldering one piece unsolders a piece soldered earlier. In the extreme case they might weld some parts, which is even higher temperature.

Hard and soft refer to melting temperature, as I understand it. The various alloys have different melting points. The references below seem to equate soft soldering to tin-lead, and hard soldering to silver soldering.

Note the the difference between soldering and brazing is the temperature. The American Welding Society considers anything over 850 F to be brazing, but not everyone adheres to that definition.

Richard

mj wrote:

WOW Richard! Thanks for all the links! I browsed through them and I got most of everything answered. It appears that my butane torch is not going to work for hard solder. My propane torch MIGHT work, otherwise I will have to look at switching over to MAPP or to a small Ox/Acet setup. Thanks everyone! Mike

In article , mj writes

I don't know much about MAPP, but I would think that Oxy/Acetylene would be much too aggressive for brass (especially in the small sizes you're discussing). You're likely to see your pride and joy disappear into a puddle. Also remember that brass is "hot-short", that is to say that it is extremely weak when very hot.

I use a propane torch for brass soldering and find it completely acceptable.

According to mj :

How big is the mini-torch? The usual propane torch is a bit on the low side for the silver soldering which I have tried, but replacing the tank with a tank of MAAP gas makes a big difference.

You may also wish to build a structure of fire brick under and around the workpiece, so your heat concentrates better.

Hmm ... that is small. See my suggestion below.

Hmm ... I understand that silver solders are available in various melting points, and that the standard practice is to use the highest melting point for the first joint, then a lower one for the next, and so on until complete, so you don't have problems with the previous joint slipping when you are soldering the next one.

Good Luck, DoN.

I've always called soft solder the alloy that is used for electrical and plumbing work, it has a melting range of 400 degrees F or so depending on the ratio of the alloys components. Hard soldering uses silver solder (or other alloys) with a melting range much higher, like 1250 degrees F or so, again depending on the alloys component metals.

I recommend the book 'Soldering and Brazing' by Tubal Cain. It really does a fine job explaining the why's and how's of what you are interested in. The best help I got from the book was how to prepare the joints to be soldered. He shows how to make an incredibly complex model, a boiler, using

13 different heats and several melting ranges of the silver solder.

Rosin core solder is intended for electrical work. You ought to get some rosin flux (Radio Shack has this) and use this with your rosin core solder - make sure that the parts are clean before you solder them. The 60/40 means

60%Tin and 40% Lead.

Roger

Right.

No: 60 tin, 40 lead.

Higher silver content will wet and flow better. In a cadmium-free alloy I'd go with at least 45% silver and preferably 56%. I like and use cadmium-bearing alloys because they work better, and I'm careful about fumes. My go-to for nearly all silverbrazing is Harman Handy Easyflo 45 or something very similar. A lot of framebuilders (bicycles) use that material.

For fine work, Brownells offers some .030 wire and thin shimstock in a cad-free 56% silversolder that works well but it won't color match brass well.

A middle ground is a tin-silver solder like Harris Staybrite. 96 tin

4 silver. It's technically a soft solder, melts a bit higher than tin/lead, but it's much stronger and wets brass beautifully. It's not as strong as a "hard" silversolder, but strong enough for many purposes. Also easier to use. You'll have more cleanup with a hard solder because of the higher heat (1250 to 1400 deg F) and flux.

Jewellers use silversolders varying in melting temp from "hard" to "easy" so they can make progressive joints. They start with hard, then go to medium so they don't melt the previous joint, and so on. A jeweller's supply place will have those materials.

Oops! That says oxy/acetylene and Smith Lil' Torch in big red letters. It is capable of pinhead-size flames. You need very localized heat to silverbraze (or even soft-solder) stuff that close together so you can get in, make the joint, get out and quench before the neighboring joints even knew you were there.

Butane and propane can do silversoldering, but they're so slow they heat everything in the region at about the same rate.

I'd use silversolder shimstock. Cut out a preform with sissors, put it between the (fluxed) pieces to be joined. Heat quickly, rapidly playing the tiny but hot flame over the joint, until the solder melts, then get outta there and squirt it with a spraybottle of water. Joints like this can be nearly invisible.

Forgive the pitch, but I happen to have a Little Torch for sale, that I never got around to putting up on eBay. It is set up for O/A with hoses and regulators. It has only three or four of the standard tips, but it also has a very interesting double-ended tip, (seen at

which allows very quick heating of the joint by surrounding it with flame from two opposite points. $195 plus shipping from Austin. I'll throw in the rest of the roll of silver solder and the flux that I purchased for brazing stainless rod. (I ended up with a TIG welder which was more suited for what I was trying to do.)

The temp at which brass gets hot-short is way far too hot for silverbrazing. If you get it that hot yer screwed anyway because you'll have long since "burned" the flux.

O/A works very well *especially* in the small sizes being discussed. The key is to use a small enough torch and keep the flame constantly in motion. Propane is OK for larger jobs, but a Lil' Torch affords the pinpoint control required for silverbrazing small stuff close together. That's why jewellers use them.

Forgive the pitch, but I happen to have a "Little Torch" outfit for sale, that I just haven't gotten around to posting on eBay. It is their 23-2003 kit set up for O/A, including the hoses and regulators for the small "MC" acetylene cylinder. Mine includes only three or four of the standard tips, but also a twin flame tip, which allows for very quick heating of the joint by surrounding it with flame from two directions. (see

I am asking $195 plus shipping from Austin, TX, and I will throw in the rest of the roll of silver solder and flux that I purchased to braze stainless rod. (I ended up with a TIG welder more suited for my purposes.)

email me if interested - emmo at austin.rr.com

I apologize for the double posting - especially given that it was a sales pitch...

Another trick I forgot to mention: Heat Fence. This is some putty-like goop that comes in a plastic jar. I found it at a welding store. You put dabs of that on previous joints you want to protect while making subsequent joints. It shields them from flame and does some quenching of conducted heat if you go in, get it done and get out quickly enough.

Wet rags would probably work as well but the goop is easier to place.

If you plan to do more of this sort of modelbuilding, I strongly encourage you to consider getting a Little Torch O/A setup. The smallest tanks you can get (MC acet, R oxy) are ample because the Little Torch uses so little gas.

The kit with tips #2 thru #6 would do everything you want. The #2 is too small for all but the finest work, the #6 can silverbraze 3/8" brass rod.

These little torches can silverbraze (or weld) ant antlers. Everyone I know that has one is delighted with it.

They can also run with oxy-propane and oxy-MAPP. I've tried that, didn't like it. I get better precision control with a smaller hotter pinpoint O/A flame. Go in, get it done, get out and quench.

Say something, Bob Swinney!

That includes regulators and tanks, right?

Right. By definition, a hard solder is a solder with a melting point above 450°C. Wellknown hard solders are silver alloys and copper alloys.

Right. And it is a soft solder.

Nick

Hi Emmo, No problem...I've double posted too.

The Little Torch setup looks pretty cool. It is a little more money than I want to throw at my hobby right now (especially after buying the mill and tools). I am going to try my butane torch and propane torch first. I am also attempting to build a resistance soldering unit (see my other post just before this one) that centralizes the heat even better.

Mike