This is probably a dumb question.
I have a piece of a saw blade (about 1/2" x 1/4") that I would like to soften to make it easier to cut and file it into a different shape. The idea is to hit it with a propane torch until it glows red and then just let it cool slowly. Is propane hot enough?
So much for the physics, but what about the practical part? I don't want the same to happen to the tip of my pliers? I presume using my vise to hold it would turn the vise into a giant heat sink? Ditto putting it on top of a larger piece of metal? I do not have any fire/refractory brick to put it on. (I don't want to use a regular one and risk it cracking in my face).
Any ideas? Am I overthinking this?
Softening metal with a blowtorch
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mooretrees
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Re: Softening metal with a blowtorch
Hi Jacob, I’m mooretree’s DH,
Is this a circular saw blade? It shouldn’t be hardened (in the sense that a knife or chisel is hardened). I have a couple knives I’ve made from circular saw blades and I just used an angle grinder to rough cut and then a hand file to shape. I didn’t heat treat or anneal but the knife works great for its intended purpose of mushroom hunting.
To address your question more directly; if you held the blade with pliers, heated blade with a torch (propane should work, MAP gas would be better considering the thickness) to cherry red, grabbed the other side with another set of pliers then heat the remainder of the blade to cherry red, your pliers will be fine. Any kind of heat treatment the pliers have won’t/shouldn’t be affected by the heat as long as the pliers don’t also glow, just don’t heat the pliers directly. Let it cool slowly, dunking in oil or water will heat treat it and it’ll be brittle unless you then anneal it.
Ymmv and I reserve the right to be wrong, as well as be corrected by those that know more…
Ps, I just reread your question, I’m not sure what material it is that you’re working with but making it glow and letting it coo slowly should make it more workable.
Is this a circular saw blade? It shouldn’t be hardened (in the sense that a knife or chisel is hardened). I have a couple knives I’ve made from circular saw blades and I just used an angle grinder to rough cut and then a hand file to shape. I didn’t heat treat or anneal but the knife works great for its intended purpose of mushroom hunting.
To address your question more directly; if you held the blade with pliers, heated blade with a torch (propane should work, MAP gas would be better considering the thickness) to cherry red, grabbed the other side with another set of pliers then heat the remainder of the blade to cherry red, your pliers will be fine. Any kind of heat treatment the pliers have won’t/shouldn’t be affected by the heat as long as the pliers don’t also glow, just don’t heat the pliers directly. Let it cool slowly, dunking in oil or water will heat treat it and it’ll be brittle unless you then anneal it.
Ymmv and I reserve the right to be wrong, as well as be corrected by those that know more…
Ps, I just reread your question, I’m not sure what material it is that you’re working with but making it glow and letting it coo slowly should make it more workable.
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jacob
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Re: Softening metal with a blowtorch
It's from a circular saw blade. I'll use the Stanley needlenose pliers then, not the Channellock 
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mooretrees
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Re: Softening metal with a blowtorch
DH says “Good choice.”
Re: Softening metal with a blowtorch
yikes! I do this all the time with some of the cheap bricks sold at Home Depot. I didn’t know they explode. I guess that makes sense if they are full of water. My two bricks are brand new and have not been stored out in the rain. They haven’t exploded even though I braze steel on top of them.
You can suspend the blade with a piece of coat hanger. I like the bricks because they reflect the radiated heat back into the part.
As for your heat treating I have done this on spring steel wire. After softening I can form the wire without breaking it.
What are you making?
You can suspend the blade with a piece of coat hanger. I like the bricks because they reflect the radiated heat back into the part.
As for your heat treating I have done this on spring steel wire. After softening I can form the wire without breaking it.
What are you making?
Re: Softening metal with a blowtorch
Can you use something inherently softer, like a piece of brass? You could use an old plumbing fitting for instance.
Even a piece of mild steel will file to shape much easier than a saw blade. As a general rule steels used to make tools of almost any kind are generally going to be much harder than steels used for something like plumbing or construction, where flexibility and toughness are more desirable attributes.
If you're set on annealing the saw blade, you'll need to let it cool VERY slowly, ideally plunging it into hot dry sand while it's red hot. Better yet use vermiculite. You need to maximize cooling time if you want to soften it to a really workable hardness. You can find Rockwell hardness/time charts for this online if you want to need out. If it's still hot to the touch after an hour, you've probably successfully softened the metal..
The bricks won't explode unless you store them underwater for a week and then nuke them in your microwave. The only time I've seen something like that violently explode were river rocks direct from the water dumped in a bonfire to heat for a sweat lodge.
Even a piece of mild steel will file to shape much easier than a saw blade. As a general rule steels used to make tools of almost any kind are generally going to be much harder than steels used for something like plumbing or construction, where flexibility and toughness are more desirable attributes.
If you're set on annealing the saw blade, you'll need to let it cool VERY slowly, ideally plunging it into hot dry sand while it's red hot. Better yet use vermiculite. You need to maximize cooling time if you want to soften it to a really workable hardness. You can find Rockwell hardness/time charts for this online if you want to need out. If it's still hot to the touch after an hour, you've probably successfully softened the metal..
The bricks won't explode unless you store them underwater for a week and then nuke them in your microwave. The only time I've seen something like that violently explode were river rocks direct from the water dumped in a bonfire to heat for a sweat lodge.
Re: Softening metal with a blowtorch
Put the metal part on a driveway or sidewalk. If needed put a few small rocks underneath to lift it off the ground. Play the torch on the metal part till it glows. Pick up the part with a pliers and drop it into a piece of fiberglass batt insulation. Cover with another piece of insulation. Come back the next day and inspect the part.