Help soldering broken bandsaw blade

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IIRC We always welded them and then did some annealing process to soften the weld so it wasn't brittle by giving shots or current after the weld and grind. Been a long time since then...LOL
I've only welded blades, not brazed them, but I'm going to guess the blade is cooling fast enough to quench it, making it brittle. After you've made the joint remove it from your jig, shine it up with sandpaper, then heat it gently by waving your torch flame around 'til the steel turns blue. You've tempered the steel enough that it should no longer be brittle.
--
Ned Simmons

On Thu, 10 Jun 2010 17:39:31 -0700, "Artemus" < snipped-for-privacy@invalid.org>
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Nearly all solder is silver, although some looks grey, and some old stuff may have rust stains on it if it's been on a rusty steel spool.
If you can wind the solder around a finger for several turns without serious discomfort, it's soft solder. Soft solders that contain silver are more clearly referred to as silver-bearing solder.
Hard silver solders are hard wire, stiffer than copper wire, more like brazing rods in stiffness. Even mild steel wire isn't as stiff as hard solders.
Brazing is the process for joining parts with hard silver solders. Brazing steel is identically the same operation, and if you've brazed steel, you're familiar with red-hot temperatures, flux flowing, etc. Oxy-acetylene or MAPP gas (used with a MAPP torch) are both capable of brazing bandsaw blades. Some say that MAPP won't work, but I've brazed and silver soldered steel parts with much more mass than the lap joint of a bandsaw blade, so I know MAPP brazes. Maybe some folks don't get the right results because of the torch that the MAPP is used with.
Silver soldering bandsaw blades can also be performed with electrical brazing fixtures. I found an old machine specifically designed to braze bandsaw blades with hard silver solder. The machine doesn't force the ends of the blade stock to fuse together the way a blade resistance welder does.. it just uses electrical current to generate heat in the blade stock joint so the flux and hard solder make a secure scarfed joint.
Electric bandsaw blade welding is generally accomplished with squared ends being butt welded together by resistance welding.
Electric bandsaw blade brazing is approached in the same way as (gas) brazing of the scarfed joint.
--
WB
.........


"Artemus" < snipped-for-privacy@invalid.org> wrote in message
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Yep, wrong stuff, as the other posters have said. If you google up "bandsaw blade brazing jig", you'll get a ton of hits, including how- to videos. Won't go into the usual rant about calling silver brazing silver soldering, you've found out the difference. If you want the right stuff at the welding supply, you ask for "silver brazing filler", or you'll end up with mostly tin soft solder. The next question will be what alloy and there you'll have to see what they have, literally hundreds of alloys and trade names out there, what I've got available here isn't going to be what anyone else will have around. You'll need the line sheet for what they carry and decide what you need from the properties listed.
Used to be HF had a cheap kit including a jig, apparently no longer. A jig can be made out of a length of aluminum angle and a couple of bulldog clips. Whack a gap in the center of the piece on one side for joint clearance, put the untouched side in the vise and use the bulldog clips to hold the blade ends in position in the gap. You can scarf the ends by flipping one, placing them on top of each other even- up and grinding both at the same time. Angles match that way and any fore-and-aft angular mis-match is compensated for if you grind things straight. You've got to have things spotless, including the silver braze itself, degrease with acetone, MEK or the brake cleaner of choice. For this sort of work, you need almost foil thickness for the filler, hammer what you get down really thin, sandwich a sliver between the ends. It was supplied that way in the kits. Flux has to match, too. The blades are pretty thin, so unless you use some really high-temp braze, a turbo torch should work. See what the line sheet says for the alloy, it'll have melting points on it, and choose one that's lower temp. Air-acetylene or oxy-acetylene will be faster, probably won't do the job any better and definitely will cost more. If you really want to go fancy, you could use some stop-off or anti- flux to keep your after-action filing and cleanup down to a reasonable amount. I've used it on gun work to keep the filler from wicking all over a part, won't do a job without it now.
Have read of hammering out a silver dime, using solid borax for a flux and a kerosene blowtorch for doing the job in a really old book, so they've been brazing ends together a looong time. A lot longer than there have been dedicated pushbutton electric welding machines to do the job.
Stan
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snipped-for-privacy@prolynx.com fired this volley in

"Smoking out" the part with an un-oxygenated acetylene flame, avoiding or cleaning only the work zone is a quick way to mask your work, and it works fine.
LLoyd
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When you say "brittle", what do you mean? Does the joint break along the braze line, or does the band saw blade material itself break? If it's the braze, then wrong material or poor adhesion (poor wetting). My concern would be the 45 degree angle. I usually scarf the joint for at least a quarter inch, maybe more. The 45 degree angle gives you about 35 thou contact, whereas 1/4" overlap would give you almost 3/8" contact. Overheating the joint just once during the process can easily oxidize the joint. Once the braze material has flowed properly into the joint, slowly pull the torch back, away from the joint, taking, maybe, 15 or 20 seconds to get 6 or 8 inches away. This will anneal the joint and redice the brittleness of the band saw blade metal on either side of the joint. You can test this part of the process with a used-up blade. If you heat it to cherry red or thereabouts, and pull the torch away, you are probably hardening the blade. Then it will be very brittle. Try snapping a piece off with pliers, both before and after this treatment. (Safety glasses required, here!). Then heat another piece to cherry red, but instead of just pulling the torch away, SLOWLY pull back, taking several seconds to get the red to go away, as I said above. Now try to snap off a piece with the pliers. The end should bend some before breaking. The reason the I generalize about some of this is that band saw blades can be made of many different materials, that act in different ways as far as hardening and tempering go. With some materials, you may have to take a longer time than I specified above to cool the part below any redness at all.
Pete Stanaitis -------------------------
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I just realized my own error on the width of the joints with various scarfs. What was I thinking? 45 degrees will give just over .025 contact (.025 X 1.414) and 1/4" will give just over 1/4" contact (0.2503122, I think).
Pete Stanaitis -----------------
spaco wrote:

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Use a TIG welder

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As usual you guys are right on target. The miserable scarf joint I had was the biggest problem. I hand ground a new one about 1/4"(a sloppy job) and (using the same Oatey solder) soldered up a real blob, but it held. Next I built a jig to hold both ends at the same time, and after fiddling with adjusting it, I got some real nice matching 5/16" scarfs. Pounding the solder wire to a thin sheet, careful application of the flux to just the scarf faces and the propane torch got me a reasonably nice looking splice. It held my weight without failing and bent at a 1/2" radius with no failure. The cross section area of the blade is .025 x .125 and I weigh 180 lbs so I calculate that's 57,600 PSI tension - well over the 15,000 PSI in actual use.
The blade is too short to go back on the saw but it gives me plenty of material to practice my technique on. They always seem break at the factory weld so I don't think I need to worry about a tired blade as someone pointed out. I'll keep the 50% Ag stuff in mind should I have problems with the wider blades. Thanks to all who responded. Art
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One tip on grinding the scarf joint. Take the bandsaw blade and twist it so that the sides that need to be ground are both on the same side and next to eachother. Then grind both ends simultaneously. Helps to get the same angle on both ends.
Dan
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On 6/11/2010 6:45 PM, Artemus wrote:

Please keep us posted.
There is a lot of tribal knowledge advising against use of 'soft solder' for band saw blade welding. I am interested to know your experiences with longevity of the joint.
Thanks!
--Winston
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Artemus wrote:

future to repair a blade and shorten a new one. One blade broke today so I went to put a brand new Lenox Diemaster 2 blade on the 4x6 and tightened it up and the adjuster went solid, on checking the blade is too long and the upper wheel hits the casting, bummer!. I've used dozens of the Lenox blades and not had this problem before, no blade welder so silver soldering will be the answer.
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On 6/12/2010 12:08 PM, David Billington wrote:
(...)

I'm interested in your results.
Please share.
Thanks!
-- Winston
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