The best way to glue two small pieces of metal together is to melt them. However welding is hot and dangerous. The second best way to do it is to melt a third bit of metal and use that as the glue. But soldering requires a soldering iron.
Although using glue out of a tube is only the third best way to join two bits of metal, it does have its uses; especially in small scale craft activity.
Which metals can be glued
The good news is that on a molecular or chemical level there is not much interaction between the glue and metal so this means that pretty much any metal can be glued. Look on the glue packaging for exceptions.
The types of metal glue
There are two types of glue that you can use on metal. These are cyanoacrylate (super glue) and epoxy resin based glue.
Epoxy comes as a separate resin and hardener which need to be mixed to a specific ratio.
Of the two types of glue for metals, epoxy provides a slightly stronger bond but maybe a bit more fiddly as you have to mix the two parts of the epoxy glue together before using them. There again, if you have ever superglued your fingers together you will know of the problems working with fast acting cyanoacrylates.
Whichever route you decide to go down the preparation of the metal surface is crucial to ensuring a strong bond.
Clean both surfaces thoroughly to remove debris and grease. I like to use alcohol based cleaner as it cuts the grease particularly well. Even the natural oils on your fingers can inhibit the glue’s effectiveness so don’t touch the surface with bare hands after cleaning. Next, take a bit of abrasive such as 400grit wet and dry sandpaper to rub on the metal to remove bumps but also to provide a keyed surface that the glue will adhere to more securely.
Each glue works best when you follow the instructions on the package closely. There are many formulas of two part epoxy resin and each has its own best drying time and rules on whether to apply to both surfaces or just the one.
The drying process
Once glued up, keeping the join under pressure whilst the glue sets is a massively important part of the process. This excludes microscopic air bubbles that otherwise weaken any glued join.
The biggest mistake that people make is to be too quick to assume the glue has fully cured.
When using super glue in particular, we all seem to remember the advertisements that promised a drying time of a matter of seconds. However the bond really should be left for 24 hours to ensure the toughest of joins.