Author Topic: Silver soldering  (Read 664 times)


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Silver soldering
« on: January 12, 2018, 10:53:23 PM »
Silver soldering is easy once You get familiar with the concept. There are a lot of videos, theory and how-to's in the WWW. Probably the best I've seen are made by Keith Appleton, who is building and renovating steam engines. He is silver soldering yellow metals which are the easiest to do.

Some metals are really reluctant on silver soldering. I have pieces of tool-steel which do not want to co-operate no matter what I do. On the other hand, the cheap steel without any fancy additives behaves really nicely. All yellow metals like brass, copper and bronze seem to behave really well. The only thing with these are that they may melt if You are not careful with Your torch. I have not tried aluminium but it is my suspicion that it is a no-go. Generally it is very hard to silver solder any materials whose melting point is below 800 degrees celcius.

In order to achieve the needed temperature (650 - 750 degrees celcius) You will need a butane torch or some other means to heat up the object. Oxy-acetylene is perfect but it is much more expensive. It is also possible to use induction heating.

The object will get hot and there must be some means of keeping it stationery while heating and operating with the silver solder. I have made a very robust set up from quadratic steel tube. This will concentrate the heat around the object and the needed temperature is much easier to achieve. The tube surronds the object with hot exhaust from the torch which is low in oxygen. This will at some degree protect the object from oxidation when heating it up. Further more the hot exhaust has a known direction. Keeping the object in mid-air is not the way to go as then You may accidentally point the torch flame into something that will get ruined or worse, catch fire.

In order to silver solder You will need silver solder. Here is an example of that stuff. There exists a lot of diverse materials to be used but I think it is better to stick with one and learn that one well. The amount that is needed is usually so small that it is easy to buy a lifetime supply of silver solder. In case You want to know more about the available materials then the Wikipedia is probably the place.

You will also need flux. I bought some borax and then I mixed it with denaturated alcohol. I also throw in a few M10 nuts. After rolling with a suitable speed for several hours in my lathe the borax particles are now small enough to create borax milk. The thing is that You do NOT want to have too much flux on the object. It is nasty stuff to clean up after soldering. Having the flux in "liquid" form makes it easy to have ONLY in the places where it is needed. The amount that is needed is really small but that small amount must be everywhere and preferably evenly where it is needed. Places without flux will not wet.

Dirt is Your enemy number one. The object must be clean. Make sure that the silver solder sticks are also clean. I usually wipe them with steel-wool to be absolutely sure that there are no contaminants around.

I have no images from the silver soldering process itself. The reason is that the process is so fast paced at times that it is next to impossible to take pictures AND do the actual soldering. Another reason is that men like me are totally lacking multiprocessing capabilities.

Usually the purpose of silver soldering is to attach two or more objects with each other. It is essential to make the arrangement in such a way that You do not need to adjust the positions of the objects while soldering. For example if You are soldering a carbide bit on a iron rod then it is not a good idea to place the bit on top of the steel rod and assume it stays there while soldering. What will happen is that the carbide bit will start wandering around as it is floating on top of molten silver solder. You will never get it accurately in place. In my example I made a slot which is tight enough to keep the carbide bit in place while soldering.

After You have cleaned the object and have applied flux to all places where it is needed then it is time to do the actual soldering. Simply warm the object above melting point of silver solder. When suitable temperature is reached, apply a VERY SMALL amount of silver solder over some joint. If all is well the solder will vanish into the joint. Do NOT put too much solder - it will only make clean up a miserable process.

After the solder has vanished into the joint You can stop applying heat to the object. Do NOT quench it especially if it was a carbide bit that was soldered - quenching will crack the carbide. Let the object cool down naturally.

This is the tool I soldered the carbide bit into. It was hardened after soldering. I made it so that the business end stayed cool enough to not to brake the joint or crack the carbide when quenching in rapeseed oil. The hardening is not really needed but the finish is nice and there will be less tool marks. When hardening silver soldered items, be sure NOT to warm the joint above the melting point of silver solder - this might ruin Your work.

Offline SwarfnStuff

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Re: Silver soldering
« Reply #1 on: January 13, 2018, 12:21:26 AM »
Thanks for posting. I knew this stuff but there may be others to which it is all new info and that is what this forum is great at.
John B
Converting good metal into swarf sometimes ending up with something useful. ;-)