I installed a brand new blade last week. About two days later, I rolled a piece of wood and put a nasty kink in the blade. Isn't that how it always happens? I had briefly experimented with brazing blades in the past, when I had a little 9" bandsaw that seemed to break a blade in the middle of every project. I gave up and bought a bigger bandsaw, because the brazed blade would still break somewhere else on every project. But I still had the crude jig I had made, and it came to the rescue. I cut the blade at the kink and brazed the blade back together. The joint wasn't quite perfect, but the blade is back in action with almost no wobble (way better than some of the new blades I've installed). I didn't even have to readjust my blade guides! Once I finished my project, I decided to make a fairly awesome bandsaw blade brazing jig, so next time the joint will be PERFECT.
Step 1: Tools and Materials
This jig only requires a few scraps of wood and 4 wood screws! The actual components I used were two 4x6" pieces of 3/4" douglas fir, an 8x8" piece of 3/4" plywood, 4 wood screws, wood glue, and a 6" scrap of 2x1". The tools I used were calipers, a hand plane, a couple of clamps, a drill press, a pencil, a try square, and a bandsaw. This jig squares the blade, like all good jigs. And it is fully adjustable for blade curvature, which is a fairly unique feature for a fairly awesome bandsaw blade brazing jig!
Step 2: Squaring the Wood
I resawed 2x6" construction lumber to get my 2 blocks of douglas fir. Since I split the board in two, it curled quite a bit. And I'm sure it's not done curling, either, since I only let it dry for a few days. This step shows how I squared the wood blocks. So if you have some flat 3/4" wood lying around, use that and skip this step.
Step 3: Cutting the Clamps
Each clamp is ultimately going to be a 2.5" x 2.5" x 1.5". They're made of two layers of 3/4" wood glued together. But I will make it as one big clamp, then cut it in half when it's finished. See the pics for the play-by-play.
Step 4: Glue Up
Next I glued the pieces together. As you can see, they form a little "tetris puzzle." The larger half of the clamp is going to be screwed onto the plywood base board. The smaller piece is going to clamp against the bigger piece by means of a wood screw. The quarter inch ledge is going to act as a fence to keep the blade halves parallel and in line with each other. The overhanging lip is on the bigger half of the clamp; since it is the side that is going to be screwed to the base board, the lip will make sure the other half of the clamp stays in line. So the "tetris" shape performs two functions.
Step 5: Drilling the Holes
These pictures show how I marked off and drilled the holes for the screws. Because my screws were too short, I had put a healthy countersink into all my screw holes. See the pic captions for more details.
Step 6: The Base Board
I used plywood for the base of the jig, because it's relatively dimensionally stable. I didn't take any pics until after the fact. But it's fairly simple. Place your two clamps onto the edge of the board so that there's about a 2-2.5" gap between the clamps. Then put in a screw and tap it to leave a mark on the plywood. Drill out the holes. Screw clamps onto the board. Then draw the part you want to cut away. (So that the board doesn't char/burn so bad while you are brazing!) Cut that part out with the bandsaw. Next, I went about attaching this "stick" to the board at 90 degrees for mounting to the bench in such a way the blade would have a place to hang, freely. But I didn't want it to be attached permanently. This would increase the bulk for something that might not see the light of day for months; hence why I tried that wedge getup. Turns out, it's not very sturdy, which is why I tried hanging the board down, instead of up. In reality, I'll probably just stick it to the bench using two bar clamps, so the cutout is facing up. (I can also unscrew and swap the clamps so the clamping screws are still accessible from the top).
Step 7: Completed Jig
I looked at a lot of jigs before making this, and this jig has a feature that I didn't find anywhere else. The reason there's only one screw holding down each clamp is so that the clamps can rotate. This takes into account any curvature of the blade. After running thousands of revolutions over the wheels, a bandsaw blade can often become a bit curved. If the clamps are perfectly in line and your bandsaw blade has a curve, your scarf joints don't line up perfectly. With this jig, you can adjust the clamps so that the two halves press against each other with positive force in perfect alignment! (It also means that none of the drilling requires any precision. In fact, the only things that need any precision are: the bottom board of the clamps must have flat, parallel surfaces; the surface of the base board must be flat; and the cut through the top board of the clamps must be square.)
Step 8: How to Braze a Joint
I won't go into any detail here. There are a lot of good resources available if you just google. First, you square up the ends of the blade with a belt sander or grinder. Then you put a 30 degree angle on each end of the blade, to make what's called a scarf joint. Then you clean the surfaces. I use acetone. Then you put the blade into the jig, tightening the blade in place with a screwdriver. Flux the ends and then line them up until everything is perfect. Then heat up the silver solder and the joint with a torch. I use a propane torch. I get the joint just up to red/glowing, apply solder, then remove heat. If you're ambitious, you can have a small scrap of wood handy with a wet cloth over the end. Touch this just onto the tip of the teeth to harden them. (Or try, at least. I doubt anyone is fast enough. Maybe if you had a very coordinated helper.) Otherwise, just let everything air cool. Then, I clean up the joint with a dremel tool with a sanding attachment.
If you do not anneal, I have found that when the blades eventually break, they will tend to break on either side of the joint, approximately where the jig holds the blade. So even a wooden jig will sink enough heat away from the blade to make it brittle. After the joint is done, let it cool, then remove from the jig. The take the torch and heat the areas around the joint for several inches and let air cool.
Also, I have needed this jig a few times, and it was a pleasure to use compared to my previous attempt. :)