I’ve heard that saying countless times and no amount of googling gave me a satisfactory answer.
In: 8838
The striking face of a hammer is harder than the body. Similar to how they harden the edges of knives while keeping the spine softer. Smack two hard pieces of metal together and they crack and fire chips at you. Also they bounce. I was working on a piece of wear plate that had hard surfacing on it, really hard alloy welded to regular carbon steel plate. There was a small pointy bit after cutting, figured I’d just give er a whack with the hammer and next thing I know I’m picking a chunk out of my cheek just below my safety glasses. Rookie move totally, same thing though.
I tried to use a sledge hammer to drive a wood maul the rest of the way through a log. Felt a sharp zip in my wrist and realized that a dime sized piece of shrapnel went through my arm near my wrist and hit the bone inside. I show kids the scar on my arm and the piece of shrapnel when I talk to them about safety. Needless to say, I don’t do this anymore.
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Lots of answers here keep saying that it’s hard, and therefore brittle. I’m going to try to ELI5 but with a little more depth:
TL;DR
* Steel can be hardened or softened
* “Hardening” involves heating, followed by rapid cooling.
* “Annealing” and “tempering” are ways of softening steel
* Soft (annealed) steel deforms easily without cracking (like Play-Doh)
* Hardened steel tends to crack when deformed (like glass)
* You can hit Play-Doh with a chunk of glass. You could hit a chunk of glass with Play-Doh. But if you hit a chunk of glass with another chunk of glass, things are going to start cracking
* If you hit a piece of hardened steel with another piece of hardened steel, you’ll tend to crack one of them
Long version
Steel is an amazing material. Its strength and hardness can vary tremendously depending on what other materials are mixed into it (alloyed with it) and how it has been processed. Many types of steel can have their strength and hardness adjusted simply by heating and cooling them in the right order and at the right speed. This is great because you can make the steel soft, which makes it easier to cut it, file it, grind it, etc. When you’re done working with it, you can give it a heat treatment that makes it as hard as it needs to be for the finished product.
At this point you might be wondering – how exactly do we define hardness, and why does it matter? Hardness is literally how difficult it is to put a scratch or a notch into the steel. Think of wood — easy to dent, therefore it’s not very hard. Aluminum (like the lid of a Macbook) is also rather soft, and therefore easy to scratch or dent. Steel is rather hard, and some steels can be VERY hard.
But hardness isn’t the only trait we care about with materials. Otherwise we’d just make all the steel as hard as possible, all the time. Another important strength is toughness. You can think of toughness sort of like opposite of brittleness. A material that’s very tough can take abuse without cracking or shattering. A very tough material can absorbe a lot of energy, say from an impact. It might bend, dent, or deform in some way, but still not crack.
Generally, with steel, toughness and hardness work against each other. If you harden a piece of steel, it’s toughness drops. That means it’s really hard to dent it or scratch a piece of hardened steel, but if you push it past the limits of its strength, it is MUCH more likely to crack. Very hard steels (like the kinds used for cutting other steels) can be so brittle that they will shatter or at least crack if you drop them on the wrong surface. On the other hand, if you anneal the steel (soften it), it becomes much tougher, and will tend not to crack even when highly deformed. Imagine bending up a wire coat hanger. It’s not going to crack.
Hammers have to be rather hard; otherwise the hammer’s head would eventually mushroom out and become useless. They also need to be rather tough, to avoid shattering. So, there’s a bit of a compromise. They try to make the hammer hard enough that it’s going to be harder than whatever you’re likely to hit with it, but not too far beyond that. That way, when the hammer hits a nail, the nail is more likely to deform and the hammer is unlikely to be dented, scratched or nicked by the relatively soft steel of the nail. And hopefully its toughness is high enough that it can still take some abuse without shattering.
When you take two hammers and smack them together, you’re hitting two pieces of relatively hard, relatively brittle steel against one another. Inevitably, one of them is slightly harder than the other, so if you hit them hard enough, you’re going to start deforming the softer hammer. But it may not be able to tolerate that deformation without cracking. If it does crack, the pieces will tend to fly off with lots of energy (both because you hit it so far and strained the metal, like a spring, and also because of any internal stresses that may exist in the metal from the heat treating process). So there’s a decent chance that you’re going to send shards of steel flying.
That’s the general reason why hitting hammers with hammers is a bad idea.
**EDIT:** Thanks everyone for all the upvotes and the awards! I had no idea anyone would find this response so interesting. I’m thrilled to have provided an answer that was helpful to so many people! Thank you for taking the time to read, and for letting me know you enjoyed it!
As many others have pointed out, hammer heads are brittle and can fracture when striking hard surfaces.
But there’s also the question of “where does all the energy go”. Because that’s all a hammer is, a method of transferring kinetic energy from your arm, into an object. If you hit a hammer with a hammer, and you’re holding both, all that kinetic energy from your swing is going to travel up the handles, through your arms, and back into your body. This will feel unpleasant at best, and really quite painful at worst.
So, to summarize. Don’t hit a hammer with a hammer because it’ll feel bad and probably break one or both of the hammers.
Because while trying to get nails out smashing two claw hammers head to head one of them shattered and I ended up with a chunk of steel in my arm that could have easily been in my eye
Mythbusters did an episode about this. You can see it tested so I would recommend you watching it. The whole show is amazing by the way… long story short they don’t explode but shards are dangerous… they tell a story about a main who had a shard in an artery
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