Soldering Brass-What Am I Doing Wrong?

[86TA355SR]

I’ve had difficulty soldering brass parts on several projects. Can’t get parts to “stick” or hold. Sometimes a part will, most often it doesn’t.

I’ve done the basics, at least I think I did-clean bare brass parts with steel wool, flux, heat, solder. I use the pen torch mostly.

Here’s what I have for equipment:
Oatey #5 paste flux
Micromark liquid flux
Rosin core 63\37 solder
Oatey solder paste (It’s my understanding paste is small particles of solder mixed with flux?).
Resistance solder unit
Solder iron station
Micromark Pen torch

1. Am I using the wrong flux? If so, what do you recommend & where do I buy it?
2. Do I have the wrong solder for this purpose? If so, what do you recommend?
3. Do you “tin” both parts separately prior to applying heat? When I try that, it’s very difficult to get the solder to melt the second time.
4. When soldering a large part, such as an air pump, to a thin bracket, Heat the large part first, correct ?
5. I heat until the solder melts, as soon as it does, I pull heat away. Is it possible I’m not getting parts hot enough for the solder to “flow” and make a good bond?

I’ve watched several YT videos showing techniques but no matter what I do, I can’t get stuff to stick.

Appreciate any help/recommendations.

[bob turner]

First off, I am officially jealous! I cannot buy Oatey's solder-filled paste, and I loved it.

Which is the first hint: go to the hardware store and buy fresh acid flux. Paste is ok - currently using "Nokorrode."

Martin can help here, but my contention is that old flux loses its abilities (just like us).

Second hint: is your soldering iron bright and shiny when hot? If not, try to get the tip shiny (a file, flux, and solder). Keep it shiny with a damp sponge.

I do handrails with a torch. Clean, flux, a tiny flattened chip of 60/40, and a propane pencil tip, short flame. Do not heat the wire; only the body. Solder will jump in there with a beautiful fillet, then get the flame outta there.

New flux!

[Rufus T. Firefly]

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[sarge]

If I'm honest, it sounds like you are tool-heavy and practice-light.

We all have different techniques and different preferences. Bob uses a torch on handrails. I use a pencil iron. Some swear by soldering paste, I detest it. I swear by TIX liquid for flux and believe paste-flux is for plumbers. Yet we both get results we're happy with whilst using wildly diverging materials and techniques, so the materials and tools are actually quite forgiving. One concludes the answer to your problem must lie elsewhere.

I would suggest you get brass scrap and practice. You'll get it, I'm sure; if I can solder things together anyone can.

Start with wire and a pencil iron. Easiest case; a little Tix on both, tin both, fixture (get used to fixturing) them together, heat them not until the solder melts but until it flows. Learn to see flow. Let it cool. Nice and shiny? Good joint. Grey or frosty? Cold joint so reheat and do it again watching for flow. Master just this with just those tools.

Take a pencil torch, a couple sheet bits, fixture them together at a 90 degree angle. Flux and tin both, then start at one end and pull a joint. Not at all difficult, was it.

You need cleanliness of parts and irons, you need heat, you need fixturing. Above all, you need practice

Your fixtures can be heat sinks, so hard wood cloths pegs carved to shape are lovely. Alligators and forceps are nice because they don't have much contact area. It sounds like you might be soldering in a vice which rarely works since the clamped piece can be near dead-cold when the other is hot.

Solder bits of junk together, scraps, wire, sheet, castings, old crap brass HO bodies you can get for near nothing at train shows so you learn how to manage heat and solder without disassembling what's already there. Learning to solder on something you actually want is a great way to get scared of it.

In soldering, the solder is pretty forgiving, the flux is pretty forgiving, the tools just need to make heat and heat-transfer. There are no mysteries, just practice practice and more practice. You will succeed and you'll discover what materials you like and what techniques work for you. (BTW, you're correct; heat from the big piece.)

So, clean, hot, fixtured, and watch for flow not melt. Practice. You can do it, and you can do it well with practice.

[up148]

If I'm honest, it sounds like you are tool-heavy and practice-light.

Boy, does that statement fit me.

[Rufus T. Firefly]

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[E7]

Back in the day when I worked in the Telco industry I had soldering iron tips that did NOT require tinning. I don't know if they have a trade name, but they are WELL worth searching out and buying.

Put your iron tip on one side of the work/part and the solder on the opposite side.
The solder (given enough heat) should flow toward the heat of the iron tip. When it flows like that you know you have a good joint as opposed to a cold solder joint where the solder will generally appear dull.

A coarse example of this is soldering copper pipe with a torch. Clean and flux the parts. Apply the solder to one side and 180 degrees opposite apply the torch flame. When heated properly the solder will flow around the joint toward the torch flame. You DO NOT have to move the solder, it flows around the joint toward the flame!

The key thing is, the solder will flow toward the heat. Remove the heat immediately when the solder has flowed.

Get some parts that don't matter and PRACTICE PRACTICE PRACTICE.

MY 2 cents!

[steamaheadstephen59]

I found for me at first, that I didn't do well with irons ( have improved since then) so I mostly use a propain torch. I have to concur with whats been said so far. If you don't have enough heat in the right places or something is bleeding the heat away from the part being soldered, your in trouble.Its been mentioned but there's a difference between the solder melting and solder flowing into the joint, maybe hold the heat a bit longer. It's frustrating at first getting this all right, but a joy once you crack it. Persist, we are with you.

[86TA355SR]

Update-I’m in business!

I bought some new flux today as recommended and concentrated on getting the solder to flow. I’m certain I wasn’t getting parts hot enough and the old flux was an issue. After it cooled, I’m glad to report parts are “sticking” and I’m a happy camper!

Soldered several projects I’ve struggled with, all with great results, now I’m making progress!

Thanks for the help/recommendations! Should have a finished model by end of week.

Aaron

[sarge]

Way hey! Well done that man.

Once its together, show it off. Then, gather some bits and practise some more. Soldering becomes no more daunting than sticking bits with glue once you've truly mastered it, and mastering it means (all together, now) "Practise".

[steamaheadstephen59]

So glad to hear its all happening, happy soldering on.

[86TA355SR]

Thanks guys, I’m happy to be making progress on many projects. Owe a big thanks to all!

For example, tonight I knocked a part loose while getting ready to paint. No big deal, soldered it back in a few minutes.

I also got the Mikado painted!

[GreggL]

Like others, I am tool heavy and practice short. And Aaron, thanks for bringing up this topic - a great one!

Two areas I have trouble with are...
Resoldering a piece on a painted/finished car. Obviously a joint needs to be clean without paint. How do you deal with these small areas, then how oto deal with the surrounding paint damage from application of heat?

Secondly, my latest toy, errrhhh, I mean tool, is a Little Torch (propane & oxygen). I certainly have learned how to melt wire and am bordering on expert level. However, lesser applications of heat are elusive. Do you wave the torch back and forth letting heat come on gradually?? Also, how do you keep brass from turning black form soot?

Thanks...gregg

[bob turner]

You might try straight propane or map gas with a pencil tip burner. Sounds like you do not have enough oxygen in the mix.
Also, usually oxygen is piped in to give a much hotter flame, as in welding or silver soldering.

George Wilson used oxy-acetylene, and was good at it, but you could see his brass went soft.

Re-soldering already painted models might be possible with a resistance setup. I just clean the paint off, then retouch.

[sarge]

Using the right tool for the right circumstances really helps here; soldering is not the place for heavy-handedness.

If you're melting stuff, its too much local heat; back off and use a pencil iron. I usually go in order from pencils to larger irons, only then on to resistance, and finally torches.

I don't silver-solder so an oxy-mix torch is just not in my arsenal; far too brutal for brass in my experience.

I suggest using the right tool (Yeah, I know. Borrrrring!) rather than the coolest tool, tempting as it is, to get the results you want.

Painted stuff. If you can get localised heat in a joint quickly, you often can minimise the paint damage to the local area. Here is where a pretty snotty resistance rig shines. I personally loathe the tweezers most seem to like, especially for repairs like this. I use copper clad carbon probes and will sharpen them to a point in a pencil sharpener for repairs on painted models. There is no other recourse but to take off the crunchy bits afterwards, blend, and touch up, but a small surface area whacked with enthusiasm minimises the damage.