Martha BryanThe author’s shop-made jig holds the scarfed ends of a broken bandsaw blade in alignment for silver-soldering.
A bandsaw is one of the most useful power tools in a boatbuilding shop. The saw can cut the curves essential in boatbuilding to a much tighter radius than a circular saw; however, unlike the blade of a circular saw, which can be used for a long time with only occasional sharpening, a bandsaw blade, even if new, may break if it is stressed beyond its designed strength. This is especially true when attempting to cut a tighter curve than the blade’s width and the set of its teeth are designed to accommodate. Also, many of us have learned the hard way that it is dangerous to try to crosscut a cylindrical piece of wood with a bandsaw: No matter how firmly you hold the piece, as soon as the teeth contact the wood it can roll into the blade, causing it to break and risking pinched fingers.
In a commercial shop or a school setting, where there may be little time for repairs, replacing a broken blade may be the best option. However, there are good reasons to repair a blade yourself: If you don’t have a spare at hand, it may be difficult to get a replacement quickly. Or if the blade is fairly new, you may be upset by the monetary loss. Some bandsaws need a blade that is not of a standard length; for example, the smallest bandsaw in my shop takes a 70″ blade, which is not readily available, and my solution has been to buy the next-longer size, remove a piece of it, then join the ends.
The jig presented here is designed to create the scarf joint needed and to accurately align the cut ends of the blade for scarfing and soldering.
1. Two pieces of steel are needed: a 9″-long piece of 1⁄8″ × 1″ × 1″ angle, and a 10″ piece of 1⁄8″ × 1″ flat bar. Cut the flat bar and angle-iron to the lengths shown in the drawing.
2. Make the cutout in the flat bar at the location and dimensions shown in the drawing, using a hacksaw for the perpendicular cuts and then a row of drilled holes, as shown, for the end cut. After boring the holes, break out the waste piece and then file to the line.
3. Make the corresponding cutouts in the angle, again using a hacksaw followed by bored holes. The objective of these cutouts is to keep the position of the blade’s scarf joint far enough from the steel to avoid excessive heat loss to the jig during soldering.
4. Fasten the pieces together using 2½” eight-penny nails as rivets inserted through 9⁄64″ holes. Also, mark the diagonal cut as shown. (I fastened the angle iron and flat bar together before making the diagonal cut.)
5. Depending on the tools you have, you may find it easier to shape each piece separately. True up the cut end with a file, at which point the jig is completed.
6. “Silver-soldering” goes by several names, including silver-brazing, hard-soldering, and low-temperature brazing. Although hardware stores often have plumbing solder, which contains a small amount of silver, a welding-supply store will carry the types of wire and flux needed for the type of metalworking shown here. The solder I use is 45 percent silver and comes in a 6′ coil of 1⁄16″-diameter wire. Repairing a bandsaw blade will use less than 1⁄8″ of it. You could probably buy two new bandsaw blades for the price of this solder; however, I have found silver-soldering so useful for a wide variety of assembly and repair projects around the shop that I do not hesitate to recommend the purchase.
Because the blade ends are relatively thin, either a propane or Maap gas torch will supply enough heat; I use Maap gas, which burns hotter than propane. (For more about silver-soldering, see my article on the subject in WB No. 215.)
7. First, square the ends of the blade with a grinder. Then heat the very end of each blade, as shown, until 1⁄4“ or so begins to glow red. Let it cool slowly. This will soften the hardened teeth of the blade so they can be filed.
8. Clamp the blade end along the jig, as shown, so that one end is even with the beginning of the jig’s bevel. File a scarf angle on this end. Repeat with the other end of the blade, filing a mating scarf. Before filing, blacken the sloping surface of the jig with a felt-tipped marker. As the filing is near completion, any ink removal will assist in holding the file accurately, thus preserving the accuracy of the scarf and jig.
9. Start the soldering operation by clamping both ends of the blade onto the jig so that the scarf bevels are in exact alignment and directly over the center of the jig’s gap. At first, keep the clamps about 2″ away from the cutout so that the blade ends can be sprung apart just enough to coat the joint’s surfaces with soldering flux. Steel quickly forms oxides that will compromise the strength of the joint, so it is best to apply the flux as soon as possible after the scarf’s ends are formed.
Then, being careful not to let the blade ends move, locate the clamps to about 1″ away from the scarf, as shown in the photograph. Heat the blade until the metal just begins to turn red. Hold the solder wire against the blade, as shown, until it melts and runs into the scarf.
10. This photograph shows a completed repair after the metal has been left clamped in the jig to cool, after which the scarf can be tapped with a light hammer or the corner of a file to break away any remaining flux. Finally, any excess solder can be filed away.
11. This 1⁄4″-wide bandsaw blade shows the appearance of the scarf after the flux has been chipped off and the excess solder has been filed away. 
Harry Bryan is a boatbuilder in Letete, New Brunswick, Canada, and a contributing editor for WoodenBoat.