On Mon, 04 Mar 2019 23:21:52 -0500, Gerry
wrote:

On Mon, 04 Mar 2019 11:56:46 -0500, Ed Huntress
wrote:

On Mon, 4 Mar 2019 08:31:54 -0800 (PST), "
wrote:

On Monday, March 4, 2019 at 7:40:11 AM UTC-5, Terry Coombs wrote:
On 3/4/2019 4:14 AM, John B. Slocomb wrote:
On Sun, 3 Mar 2019 21:16:51 -0600, Terry Coombs
wrote:

* I've read about it somewhere , but don't recall the details ... Broke
the last (nearly new) band for my horizontal , figured I have nothing to
lose but a little time , a bit of shield gas and some 'lectrons - oh ,
and I'll need to make a clamp block to keep the blade aligned as I weld
on it . Got a new blade on the way , but just got a bug to try this . I
know low amps DCEN , what filler ? Got ER70S2 ,ER70S6 (MIG wire) , ER
308/309/312 and some Invar 42 nickel/iron . The blade is an Irwin (IIRC)
bimetal 10/14 pitch . Am I going to need to anneal the weld ? O/A torch
OK for the task if it's needed ? I know I want to minimize the HAZ .
For whatever it is worth, I seem to remember a band saw with an
attached blade welder that clamped the blade in a holder with two
sections, a fixed clamp and a movable clamp. When you hit the switch
the current was applied and the spring loaded clamp moved that end of
the blade toward the fixed end of the blade, sort of like a spot
welder. There was no filler material. When the weld was finished there
was some "bead" on both sides of the blade and the welder had a small
grinding wheel attachment so that the weld "beads" could be ground
smooth. No annealing or filler metal

Earlier on we used to grind each end of the blade to a knife edge, and
then overlap the ends and silver solder them together.

Given that most band saws have large enough wheels that the blade is
not bent sharply I suspect that the joining is not a really critical
thing.

--
Cheers,
John B.


* I used a band welder of that type long ago in a place far from here .
BUT the one that I used did have an anneal function , and it did help
extend blade life . I suppose I could rig up something to do that butt
weld using my TIG welder as a power source ... it has a spot weld
function .


Snag
Yes , I'm old
and crochety - and armed .
Get outta my woods !

I would suggest ordering some silver solder and flux. Band saw blades can be tig welded, but it is easy to screw it up. Silver solder is easier. Mean while make a jig to hold the blade and try tigging. You can anneal using a hand held propane torch.

Long term make a band saw blade welder. A microwave oven transformer can be rewound to have a low voltage winding.

Dan

If you want to ake a big project of it, that would be one way to go.
But, as Gunner said, it's hard to beat scarfing the break and
silver-brazing it with O/A. That, too, requires a jig to hold it, but
it's a simple one. It's not used in industry as often as it once was,
because it's not as fast as just placing the ends in a jig and pushing
a button.

It's not widely recognized that a properly-gapped and -heated silver
braze joint can achieve over 100,000 pounds per square inch of shear
strength. You won't quite achieve that with a simple jig (the gap is
catch-as-catch-can; ideally, it's around 0.001 - 0.002 inches), but it
still is stronger than the parent metal, because the scarf multiplies
the joint area by a factor of three or so. Just the bulk strength of
the silver braze metal is on the order of 1/3 the strength of the
blade. And the embrittlement problem that comes from heating and
self-quenching with electric welding methods more or less solves
itself.

I used to do it, but I haven't broken a blade in a long while.
El-cheapo propane torch works fine for me! My jig is a piece of
channel with angle attached and clamp screws to hold the blade between
the flange of the channel and the inside of the leg of the angle and a
gap cut in the flange of the channel to let the flame come up under
the joint. To scarf the joint, I just clamp two ends together and
touch them on the grinder. After brazing, I do touch up with the
Dremel.

G That's about the level of sophistication of the rig I used, when I
was bandsawing metal -- right down to the Dremel.

Now I bandsaw wood and composites. No breaks for years.

--
Ed Huntress