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Thread: Making up band saw blade problems

  1. #1
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    Default Making up band saw blade problems

    Band saw blade silver brazing, some rambling on

    Have had fairly good success joining blades using silver brazing (high temperature silver solder without lead) on regular high carbon blades.

    Bi-metal blades was another story and most blades would break with very little use. Frustrated started making changes and plan was to improve anything I could and then go backwards and see what the one big thing was that caused the failures.

    First thing was making a grinding jig to make precise scarf joints. Believe the scarf surface is about 3 and half time the blade thickness. The jig fits on surface grinder but think a fixture could be made where a hand held angle grinder could do a good ‘nough job.



    Was using a shear to cut the blades to length. Close inspection showed that the shear was distorting the blade so started cutting the blades using an abrasive cut off wheel. This worked good and there was no sign of the blade “cupping”.



    Thought these two improvements should bring success. Cutting up an old ¾” wide blade and doing a bunch of test samples showed only some improvements and not much better then a fifty-fifty chance of a good joint.

    There was two types of failures. One was improper annealing and breaking of the blade close to the joint. Sanding or polishing the joint to a bright color and slowly bringing the heat up with a hand held small propane torch to get an oxide color seemed to work good. This was done while still clamped in “soldering” fixture. Annealing without being clamped in place did cause some poor joints that failed.

    The other was failure at the silver brazed joint. Studying the joint failures showed there was was too thick of silver brazing in the joint.



    Tried the blacksmith method. Put sliver of silver braze in joint, fluxed and squeezed joint shut with hot tongs. This made a nice thin joint but there was lots of burnt flux which was hard to clean off and it required holding the tongs tight for a long time for the joint to cool enough. Letting pressure off of tongs before joint had completely frozen was a sure way to cause a weak joint and failure.


    Continuing in another post due to 4 photo limit per post.

  2. #2
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    Putting the silver braze in joint before heating insures getting the right amount in the right place at the right time.

    I have some 1/32nd diameter Silvaloy45 on hand and am lucky enough to have a rolling mill. Running it through the rolling mill several times was able to get it flattened out to between 2 and 3 thousands of an inch thick. It can also be hammered flat. Not sure what the proper way to anneal silver braze is. I wave a propane torch over the wire a few times and hope for the best. In small diameters it is very easy to burn off some of the lower melting metals in the alloy. Silver braze can also be bought at jewelry supply place in thin sheets and then cut with a scissor to size.

    Clamping the blades in fixture and measuring the thickness of the lapped joint first so it no more then thickness of the blade. On scarf joints done on fixture in surface grinder it is easy to eye ball the overlap and get it right.

    Add just a little paste flux in joint and then slip in a thin strip of silver braze. I like a little sticking out both ends of blade, this makes it easy to see if it is lined up right.



    Add a bunch of paste brazing flux to top and bottom of joint.

    Should of set up a tripod and showed picture of heating the joint. Methods tried are a hand held torch below only, above only and moving back and forth from top to bottom.

    Using oxy-acetylene with welding tip and trying the same three methods.

    Using oxy- acetylene with small Smith Little Torch again with all three methods.

    None of them were consistent. Some good joints and some bad joints and all with some burnt on flux.

    Having two hand held propane torches, talking the kind that screw on a propane bottle. Tried two torches one pointing down from the top directly on joint and keeping the flame at the hottest point at tip of flame and not getting the cold inside of the flame on the joint.
    At the same time the other torch with the other hand is doing the same only pointing directly up from the bottom. Making sure both flames are pointed square at the blade and not at an angle, so the most heat on the blade in the shortest time.

    To insure a tight joint a hinged arm was added to soldering jig that when swung over joint it had a pointed stainless steel rod that pushed down on center of joint.



    Wow, in twenty to twenty five seconds the ¾” wide bi-metal joint was done. The silver braze had melted completely and then the hand holding the top torch was set down (one of those torches when you let go it shuts off) and the hinged joint with the finger was placed on the joint giving a little pressure on the joint to make sure the joint stayed tight while cooling. The lower torch was slowly drawn back from the joint.

    When the joint cooled there was no burnt flux and the clear flux was easily scraped off.
    A little sanding to brighten up the metal and slowly heat to show some sign of color. Think anything around tan/brown should be good for an annealing temperature.



    Beautiful looking joints that cleaned up easily. Was happy camper, was sure had figured it out.

    Wrong again, still some failures. The samples tested ok but the blades wouldn’t last long on the saw. What the heck, been working days on this, trying to do every thing right.. Then by chance put a straight edge on the machined edge of the soldering fixture that the back edge of the blade rest against. It wasn’t straight. Guess cutting the notch out of the fixture for where the area to heat the joint was caused some relief of stress and the fixture warped.
    Guess the back of the blade not being straight put lots of stress on the joint at one point. Thinking regular carbon blades might stretch to relieve some on the crooked joint but the wider bi-metal blades say no to the stretching.

    Couple of hammer blows put the fixture back into alignment. Fairly confident got it figured out now. There is no tell tale sound when the saw blade joint goes over the cut or no “bump” either. The saw had been telling me but I was ignoring it.
    Last edited by gary hart; 08-12-2010 at 03:16 AM.

  3. #3
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    Could you just be buying too thick of a blade for the wheel radius? Sounds like your having an awful time getting it to hold..

  4. #4
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    I was given to understand that the two faces of the scarf should be fairly rough- as in ground with a coarse wheel, not smooth like a surface grinder would give. That gives the solder a textured surface for a better hold.

    I haven't tried it yet myself, but it might be worth a test.

    Doc.
    Doc's Machine. (Probably not what you expect.)

  5. #5
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    Model Engineers Workshop recently had an article on joining blades. They were MIG welded, ground and annealed. Whenver I've needed to join a blade I've used the electric resistance welder-grinder-annealer on the side of the big Startrite bandsaw at work.

  6. #6
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    I've had good luck with the TIG welder. Start with a nice square butt joint and melt together with just a dab of filler so it's not undercut.

    I've used steel filler but I've heard of others using stainless.

  7. #7
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    Thanks for the excellent write-up. I've seen the procedure written up in a few sentences like there's nothing to it. Hasn't been my experience either. Will incorporate your ideas netx time.

  8. #8
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    I've TIG welded my .025 x 1/2" blades in the past with good luck. Some have lasted over a year before failure at the joint. You have to clamp the blade to a piece of stainless or copper plate to heat sink it or you will melt the edge. Some I had to aneal and some I didn't, it just depended how they cooled, it was really hit and miss.
    It's easier if you have the blade welder.

    JL...............

  9. #9
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    mig welded mine - wasnt easy but after several attempts on an old blade I got the right settings and technique...

  10. #10
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    When annealing, take it till it just turns blue. That should give it a hard spring temper and still be well below the braze temperature.

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