Help soldering broken bandsaw blade

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Reply to
Wild_Bill
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Here's a source of 56% silver solder in foil form:

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This alloy flows freely at 1205F (652C), which is a dull red.

If your propane torch will get your workpiece to red heat, it is sufficient. It's easy to overheat when silver brazing. Patience is a good thing.

Get some "black flux" at a welding store. Other silver-brazing fluxes will work, but black flux tolerates overheating which most beginners do because they get impatient.

Reply to
Don Foreman

I have been using a propane "Turbo Torch" for silver brazing for many years. I think that the largest Item I ever did was a 4" brass drain elbow joined to a toilet floor flange - I had to cut both pieces to reduce the cover (concrete floor) over the top of the pipe to less than an inch. The home owner had attempted to instal the toilet on top of the stub left by the original construction contractor then brought home another bag of "sack crete" every night to raise the floor up to support the toilet - WHAT A F * * * *D UP MESS ! Gerry :-)} London, Canada

Reply to
Gerald Miller

On Jun 10, 6:39=A0pm, "Artemus" wrote:

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

Reply to
stans4

Winston fired this volley in news: snipped-for-privacy@news3.newsguy.com:

Plumbing solder is a "soft solder". It's designed to melt at low temperatures, is brittle when frozen, and is NOT designed to be structural in any sense -- it's job is to seal a joint well against leakage when sweated properly.

Your knife repair would have been better served by making the repair with a good hard solder, then re-hardening and re-tempering the blade.

LLoyd

Reply to
Lloyd E. Sponenburgh

snipped-for-privacy@prolynx.com fired this volley in news:45566318-1852-4a1d-8b86- snipped-for-privacy@y11g2000yqm.googlegroups.com:

"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

Reply to
Lloyd E. Sponenburgh

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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Reply to
spaco

Use a TIG welder

Reply to
Rusty

Yup. That makes sense. Thanks!

--Winston

Reply to
Winston

I've also silver brazed my blades for many years but slightly differently.

The 30 deg bevelled blades are held in a simple open jig with small G clamps.

An 0.005" feeler gauge (subsequently withdrawn) spaces the two ends to provide a proper capillary gap.

The gap is covered with a thick wodge of flux. A very short snippet of silver solder wire is embedded within this flux - only enough solder volume to slightly overfill the 0.005" nominal gap

With the blade horizontal (flux + solder on top) the UNDERSIDE is heated with a propane or MAPP gas torch. This gives complete visual control of the heating process without danger of under or overheating. As the temperature rises the flux, while still covering the solder, melts and becomes transparent. You can then observe the exact moment when the solder melts and flashes into the joint.

This consistently produces clean reliable joints which require little or no dressing after brazing.

Jim

Reply to
pentagrid

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As they use a butane torch I doubt they really are brazing.

what's wrong with drilling a hole in each end and running a rivet through it?

;~)

Reply to
Leon

"Leon" fired this volley in news:G4Odncn74PZ3FI_RnZ2dnUVZ snipped-for-privacy@giganews.com:

MY bandsaws have guide rollers. mebby yours don't...

LLoyd

Reply to
Lloyd E. Sponenburgh

Thump! Thump!.. Oh Sh&t!! It just tore a great big hole in my metal piece when the rivet went by again.

That would be like putting a volt through the middle of a handsaw blade.

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As they use a butane torch I doubt they really are brazing.

;~)

Reply to
Josepi

And a big, woooosh over both of you.

Reply to
-MIKE-

Flying rivets are too small to woooosh. ;-)

Reply to
Michael A. Terrell

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> As they use a butane torch I doubt they really are brazing.

I've just read the manual for that welder...

You chaps are allowed to play with guns, why don't you do something useful with them and reduce the number of lawyers infesting your country :-|

Mark Rand RTFM

Reply to
Mark Rand

Excellent idea. Where on the lawyers should we drill? I'm guessing heart area, plenty of room where the heart should be.

techomaNge

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Reply to
Comrade technomaNge

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

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spaco wrote:

Reply to
spaco

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>> As they use a butane torch I doubt they really are brazing.

They breed.

The number of women in law school greatly exceeds the number of men.

It's terrible.

Reply to
HeyBub

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As they use a butane torch I doubt they really are brazing.

No, they are not. Are they being serious? That little torch is a joke. I have a couple and they will not heat anything unless it is very small. I would not be surprised if the solder joint as demonstrated were rather poor. The saw blade is going to conduct the heat away from the joint faster than that torch will heat it even if you *can* keep it lit :-) Note that the picture of the final result in the video was not seen well, if at all.

OTOH I wonder if using one of these pastes would be an option. I like the concept of precise application to the joint:

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Has anyone used them?

Reply to
Michael Koblic

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