> Can an equivalent length of available-size blades be welded together (maybe trimming the ends first, if they lack teeth)?
I don't think so, these blades are very narrow and thin -- 0.2mm x 0.3mm cross section at the spine -- and I'm pretty sure a weld would not hold and if it did, you'd still have to grind it down flush. And I'd guess the joint would also fatigue which is an issue since the blade needs to get wound/unwound repeatedly during cutting. Also, I think the heat of the weld would probably effect the already hardened steel.
> I wonder what the required blade tension would be
The tension on existing scroll saws is 10 - 20 lbs for blades of this size.
> how machine will maintain tension on the blade
The blade gets unwound off a spool which maintains the tension through a torque motor.
> I wonder why the blade needs to be so long.
Minimum usable length is ~10m, but I figure if you can make 10, you can make 50. The longer the blade, the longer you can cut before you have to rewind. And the longer the blade lasts before the teeth are dull and needing to be replaced
Not if it was a fillerless weld.
>I'm pretty sure a weld would not hold
...thoughts on why a full-penetration weld not be as strong as the parent material?
>I'd guess the joint would also fatigue
This is based off of previous experiments? Conversations with a metallurgist? Other?
>The longer the blade, the longer you can cut before you have to rewind.
Any particular reason the reciprocating action of a normal scroll saw doesn't work for your application?
> Any particular reason the reciprocating action of a normal scroll saw doesn't work for your application?
It works... just not well. Reciprocating is only 50% time efficient (only cutting on the down stroke!), wears out the blades by rubbing on the up stroke, and the very small length wears out quickly so they have to get changed often
A pulse of GTAW. You can set your welder to just give a short duration weld pulse, and you'd have it set so that a single pulse would complete the weld on the saw blades without using filler material. Search on youtube for people welding razor blades together to get an idea.
At that length, you would need a jig or straight edge to keep it linear, not to mention a large space. But it does not seem impossible.
Maybe ask a number of machine shops or even a general contractors to assemble it for you, suggesting this method, especially if you bring the supplies? I would try a small prototype first.
The punch and die shops probably focus on their specific type of product (punches, dies), so I would look broader.
Or maybe put the project on the Handy app? (A hungry person may be happy to do it for you, not thinking more than twice about how unusual it sounds.)
Asides: I wonder what the required blade tension would be and how machine will maintain tension on the blade. Also I wonder why the blade needs to be so long.