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Ed's Excellent Soldering Thread

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  • Ed's Excellent Soldering Thread

    Soldering is a very basic skill. Fortunately it is easy to learn. You need:
    - Metal parts that CAN be soldered, primarily copper, carbon steel and brass
    - A means to clean same -- a chemical 'flux'
    - A suitable solder -- usually electronic grade
    - A way to hold the parts together -- fixturing
    - HEAT -- from a soldering iron, gun, or a small torch

    I ignore all advice concerning rosin fluxes. I only use acid fluxes -- either liquid or paste. You can count on them to clean and activate the metal surfaces. Rosin fluxes, in my highly qualified opinion, are frustrating and useless.

    Acid fluxes are not all that acid. They do boil, smoke and spray droplets during the soldering process. You want to protect your eyes from the spray. Breathing the smoke isn't recommended. And it may be wise to clean any excess flux off your finished part. But as industrial chemicals go acid soldering flux isn't going to eat your face off. Not for a while.

    I also 'tin' the end of my soldering iron or gun -- I often need to start by filing the tip to bare metal to remove any grunge, then I'll dip the hot tip in acid paste flux, and then apply solder to coat the hot tip of the tool. Once tinned, I will often dip the hot tip of my soldering tool in acid paste flux to clean it again. When the tip gets grungy I'll file it clean and start over.

    I will apply a bit of solder to the tip of my soldering tool to help conduct heat to the metal I am soldering. Just so a drop of solder clings to the tip of the soldering tool, so it can form a bridge to the 'work' when the tip of the tool touches it. For light soldering jobs that little bit of solder may be enough to make the joint.

    Often it helps to 'tin' both parts you want to join. This is especially helpful when wiring or making fine, precision joints. Apply flux and solder to each of the parts independently, so their surfaces get a bright solder coating. Then when you go to join the parts it will be easy to get the added solder to 'wet' the tinned parts and form a joint. On some small assemblies the solder on the two tinned parts will be enough to form the joint. Just a quick touch with the soldering tool will be all that is needed to form the joint. This is especially useful when soldering metal parts -- such as brush tubes -- that are in contact with plastic. If you keep the heat quick and local you can often avoid damage to the plastic.

    Applying enough heat to the metal to be joined is critical. That, and adequate flux. If the joint is properly heated and fluxed the solder will flow into the joint. If that isn't happening, the metal is not properly cleaned or heated.

    Small parts, especially wiring, should be heated with a low wattage (25 to 35 watts) soldering iron. Larger parts may require a soldering gun (100 to 200 watts) or a small propane torch. I will jump up to a torch for some chassis soldering. It will do the job quickly when other tools won't.

    The operative word there is 'quickly'. Don't use any more heat than needed to get the solder to flow. Also be aware you can SET FIRE to things if you aren't careful! BE CAREFUL! Really, be careful!

    Good fixturing is a terrific help. Sometimes it takes ingenuity to figure out how to hold the parts in place, but that is worthy effort. Good fixturing can make a precision soldering job easy. Especially if you are going to make more than one such joint.

    Am I an expert on soldering? I am NOT! There are real, bona fide soldering experts in the world. I'm just telling you what has worked for me. It should help you get off to a decent start and help you develop your own skills.

    Ed Bianchi

  • #2
    Re: Soldering--

    I am not as good at it as the big boys here, but the lead-filled solder smoke always seemed to invariably make it up my nostrils (which may account for a lot...).

    I now use an old (and larger) computer fan that I sit right next to my work to suck the fumes away.


    • #3
      The iron is not a spatula!

      Sweating solder is pretty easy. I've been burning all manner of stuff for years and years. I'll use my latest drop spindle module for some visual

      The biggest failure point in soldering is lack of heat across the entire joint. Technically the solder should not touch the iron, unless you happen to be tinning the tip or small wires. Once applied to the project, it should always remain in contact, save for a few exceptions. If the solder doesnt blow off the tip, yer not hot enough.

      Note: See the first burn? I cleaned and inspected the frame rail, axle beam joint. It was isolated with a heat sink and the backing plate was soldered on the spindle. This way I can immediately see if I compromised the first joint and so on as I progress. I always clean up after every step, so I dont solder myself into a corner and have to back up to correct a fatal flaw....dont ask! LOL

      The backing plate shown above in the first frame was re-fired. It had a cosmetic pock in it, so I heated it right back up and let the old solder slough through and out the bottom. Then I rapidlly wicked in a fair amount of excess solder and let it run right through. With that excess, comes excess flux as well; that scrubbed out the offending particulate or "greazy what have you" while resoldering the joint.

      All that crustified sauce is just spent/oxidized flux. What is significant is that what lies beneath it is all squeaky. It just blows off with a wire wheel in the dremel. Obviously a huge nono/failure, were it an electrical connection; but there's more than one kind of soldering. Reworking electrical joints is quite another matter/skill set entirely. Reworking mechanical joints is no great shakes, so I included the theme with the thought that it is just as important to know what to do when "doing it" in the first place goes awry! It just coincidentally happened 2 weeks ago. LOL!

      Note: No globs or hangers! If the solder doesnt run cleanly out the bottom as shown, yer still a might cold.

      Typically you like to plan your joints so that they can be heated from below because heat rises, but life isnt always optimum. Soldering takes a matter of seconds. Staging the job is what takes the time. Clamps, gator clips, forceps and a good hobby stand are not optional. You cant heat a joint correctly thats wandering around or wigglen'. The top of the joint will start smoken a bit when its close to ready, tease the solder on top and when correct temperature is attained it will freely wick down through the joint .... POOF! I cant over emphasize that you have to wait patiently for the joint to heat up, BUT you must have the iron in good contact for that to EVER happen. Steady!

      Mechanically captured joints work better than free wheeling butt joints or other ill conceived imagineering situations .... LOL. Typically, I like an index hole, a slot, a cradle, a sleeve to support my joints.

      Aside from "heat rising" and isolating your previous work, allowing an escape for excess is not a bad idea. It not being a perfect world, I like to have an exit for any liquid solder to escape or free fall from the project, should things become less than optimum.

      Gators and forceps arent just for clamping. Heatsink theory is "soldering 101", when you get beyond the single hits and blips, and start laying out more complex assemblies. Here Im backing the the horizonatal frame connector (behind) from the axle beam frame rail joint. Otherwise the whole shebang butters up and goes buh-bye.

      Welding is quite another matter, and has no practical application in slotcars. It requires a fair amount of commitment. Best to take the introduction at the local JC or Voc-tech, unless you have someone qualified to teach you. It requires steady nerves, and a fair amount of control over your instincts and automatic reflexes. Some people just dont respond well in proximity to molten metal, plasma arc, and all the fun and games associated with "dancing with fire".

      Some guys can't handle the claustrophobia of being chapped and hooded up, let alone upside down, backwards, or out of position. They always make it look pretty and glamorous on the tube when they are stacking dimes with a TIG on a perfectly staged joint. Unless you're in high end production its NEVER gonna be like that. LOL!

      Seriously though Nick, I whole heartedly encourage learning how to burn.
      Last edited by Wet Coast Racer; 01-12-2018, 06:56 PM. Reason: Removing extraneous content


      • #4
        A few advanced soldering tricks...

        Using heat sinks to protect existing soldering work from the next bit of soldering -- as described above -- is a very useful technique for advanced soldering.

        Something else I have used -- masking areas with rubber cement. Rubber cement -- once dried -- stands up beautifully against acid fluxes and the heat of soldering. Easy to apply with a toothpick and easy to remove. I have used it to keep solder off of gear teeth when I'm soldering a gear to a hub. Also to keep solder out of the threaded hole when soldering a nut into an assembly.

        And a Gerry Cullan specialty -- using solders with different melting temperatures. Again, so solder joints you have already made aren't melted when you make the next one nearby.

        Then there is solder wicking braid. Very fine braid pre-treated with a solid flux. Used to remove solder from a part. You heat up the part and touch the braid to it. The braid sucks up the liquid solder. Can be very helpful in removing excess solder from a joint.

        Received wisdom is that a strong mechanical joint makes for a strong solder joint. See if you can make your joint a mechanical assembly before you solder it. Can be done by press-fitting, folding sheet metal, crimping, or wrapping the joint with thin bare wire. I have also used purchased 'hairpin' spring clips to hold brass tubing together to form a 'T'.

        I cut off most of the wiggly stuff so I just have the straight bit, to fit down the center of one tube, plus that nice tight circle to hold a larger brass tube in place as the top of the 'T'. Great for axle bushings.

        Whatever works!

        Ed Bianchi


        • #5
          Between welding and soldering there is brazing -- something like soldering, except you use a brass or silver alloy in place of solder. Brazed joints are much stronger than soldered joints, and are almost as strong as welded joints.

          Brazing does not melt the parts being joined, like welding does, but the parts do get hot enough to glow. Only the brass or silver actually melts, and flows into the joint much like solder does.

          Brazing takes much higher temperatures than soldering -- around 1,000 degrees Fahrenheit. You need a torch to get those temperatures -- either oxy/acetylene or MAPP gas. Propane just won't cut it.

          MAPP gas is bottled like propane, and does not need an oxygen supply other than ambient air. It burns hot enough to do brazing, and is a whole lot cheaper to set up and use than oxy/acetylene.

          I have used brass brazing to repair motorcycle accessories. It is way easier to braze than to weld, and a brazed joint can be tougher than a welded joint. That is, a brazed joint can deform more under load without breaking.

          I have never used true brazing to build a slotcar chassis, but there is a near cousin that I've used extensively. The product is called 'Stay Brite', and is purported to be a silver solder. It comes with its own liquid acid flux, called 'Stay Clean'. You can use Stay Brite with ordinary soldering tools -- it does not require the high temperatures of true brazing. But it still makes stronger joints than ordinary solder.

          Stay Brite will also solder materials that ordinary solder won't. I have used it extensively to solder stainless steel. The Rattler Mark 2 uses Stay Brite solder to make joints between brass and stainless steel.

          Ed Bianchi


          • #6
            To begin with...

            Get the parts stabilized. Sometimes I weight them with pliers and whatnot.

            Get the tip hot, clean it off with a paper towel, "tin" it with solder.

            Put a tick of flux on the parts.

            Heat with tip of iron, touch the tip with solder (yeah, I know yer not supposed to), when it melts, move over to the part & see if it will melt there. If so, let it flow into the area to be soldered. When the joint is shiny, you are done.


            • #7
              There is another option when it comes to high-strength solder. It is brand-named 'Tix' and is available from Micro-Mark.


              I haven't used Tix for any of my slotcar chassis. It seems to be harder to work with than the other solders I use. Your best bet is to use it with the Tix-specific flux.


              Tix also sells a rather unique product called Anti-Flux. You brush this stuff onto surfaces you want to keep solder off of.


              My own preference is to use rubber cement for the same purpose. But there may be instances where Anti-Flux is a better option.

              I haven't had much experience with Tix products, but I mention them all here just to make you aware they exist.

              Ed Bianchi


              • #8
                Thanks, this is a great article. Both of you are really skilled. Thank you for sharing your knowledge and experience. This is very helpful.


                • #9
                  I like to use acid core silver solder for chassis work, it makes for stronger joints than you get with electrical solder. That may not be as important with HO cars however. When you use acid flux it is a good idea to rinse your work with water that has some bicarbonate of soda in it or anything made of steel will eventually rust badly.


                  • #10
                    I use 3 soldering products:

                    Tix - excellent for brass and nickel - low temperature melting

                    Sta Brite + Stay Clean flux - a little higher melting than Tix, a bit stronger and very good for stainless steel

                    Silver solder (brazing) much stronger than solder but needs a higher temp. Some torches will do it but I prefer resistance soldering. My small set up can generate the equivalent of a 900 watt iron in a small area.

                    Auto Union front axle assy.

                    The stub axles silver soldered - the rest of the work with Tix



                    • #11
                      I've heard about resistance soldering, but have no experience with it. Can someone contribute a post on it?

                      Ed Bianchi


                      • #12
                        Originally posted by HO RacePro View Post
                        I've heard about resistance soldering, but have no experience with it. Can someone contribute a post on it?

                        Ed Bianchi
                        A quick answer then I'll look for more info. It's rather like arc welding lite. The basis is a transformer with very low voltage high current secondary. There are two leads - often one ending in a clamp and the other a carbon electrode. The ground clamp is attached to the work and the electrode applied at the joint - a short circuit is created with intense heating at the point of application. It is very fast. Other tools are insulated tweezers with electrodes at the tip or pliers with a similar configuration.

                        There are several advantages - very high temperatures are available - silver brazing is easily done. Because the area heats so quickly, the process can be completed before the heat has spread far from the joint - the heating is very precise. I use a carbon electrode and a foot switch to control power.



                        • #13
                          EM, I'm a curious critter and am intrigued by your application of resistance soldering. Is the gear you use a commercial setup in a domestic environment or is it something that can be made with commonly available parts? Is there any chance of some photos of your setup please. Thanks for any additional info.



                          • #14
                            The one source I know for resistance soldering equipment is Micro-Mark:


                            From their website:

                            Cheapest Set:

                            Value Set:

                            Most Expensive Set:

                            Again, I have no experience with these tools. But I have had episodes of lust concerning them. I've been off-put by the investment required, but I strongly suspect, if I ever take the plunge, I'll regret not having done so sooner.

                            With luck we'll have more input from folks who have experience with tools like these.

                            Ed Bianchi


                            • #15
                              In my experience, Micro Mark is a very expensive vendor. (their typical trick is to raise the listed prices just before a "sale") I use them when I cannot source my needs anywhere else.

                              My set up was an eBay buy - used:



                              The 3 binding posts provide different levels of maximum power when connected 1-2, 1-3, 2-3 and the rotary switch offers further adjustment. It does take some experimentation to determine the best power level


                              A joint in heavy (0.0625") brass:

                              The electrode was applied to and drawn along the inside of the joint and solder applied to the outside. You can see that, in addition to forming a solder fillet on the outside, the solder was drawn through the joint to the inside.