This will assist in repairing a broken blade or in making your own blades from coil stock or auction site blade stock. First, you will need some blades. I like to buy coil stock if I can get it for a good price, or I buy blades in bulk that are a little longer than I need. I will cut these down to length.
To solder the blades, you will need silver solder and flux. I use silver solder that I got at the hardware store, and a boron modified flux that I found at McMaster Carr. The boron modified flux gets a better bite on ferrous materials like blades.
You will need to know the finished length of blade that works on your saw. To get the measurement either check the owners manual or take a used blade and cut it to measure. I add 1/8” to the total length to allow for the solder joint. Cut the blade to length using a snips.
To make a strong solder joint you will need to grind the ends of the blade at an angle to create a “scarf joint”. Ideally this should have a ratio of 6:1 joint face to blade thickness. It’s not really critical so I usually shoot for about 1/8” solder surface in the joint.
To ensure alignment of the finished blade, I use a jig that I welded up put of a piece of angle iron and a couple of steel strips. The center is cut out to provide room to solder the joint.
Slightly bend one of the blade ends to make the pieces spring together and ensure a tight solder joint. Clamp the prepared blade into the fixture and apply flux to the ends. Pinch the ends together and feel to be sure that there is no “bump”. If so, adjust until the transition is smooth. Cut a piece of silver solder the length of the joint and place it between the blade ends.
Heat the joint to dull red with a propane torch and watch for the solder to flow out. Hold the heat for a bit to make sure everything is hot enough. The solder will sweat the joint and flow where there is flux.
Let the blade cool in the fixture and grind the face of the blade smooth. Remove from the fixture and grind the other side smooth. Feel to be sure there is no lump at the joint. Last, grind the back of the blade and smooth the edges with a file.
The finished joint should show as a narrow band of solder. The blade is now done and ready to use!
-- Minnesota Woodworkers Guild, Past President, Lifetime member.