The Magma Hammer Is built over a volcano. Water drips from above in 7 places in the center of the U-shaped catwalk and the cave in's knock invaders into the volcano where they sink, burn and disappear. Nice and clean. Also the entrance, magma hammer chamber and/or outdoors can be flooded with large amounts of magma.
Two levels down is a by-passable bridges drop pit and a constructed floors on supports drop pit; here shown trapping elves for slaughter.
Magma can be pumped all the way down to the depot and fill the drop pits as well.
Also that dwarf has about 4k kills.
Oh hey, my magma hammer design! Nice to see it in action.
I never actually built a magma hammer myself. It was purely a theoretical thing that existed only in my head. However I've got a thorough understanding of DF physics and gameplay by this point, so I don't actually need to build something in game.
As fun as the magma hammer is, I just had a lot more fun having my dwarves fight in glorious hand to hand combat. My fortresses are full of warrior-poets. They're out on the battlefield slaughtering infinite invaders from a dozen hostile civilizations laying siege, and then decorating their weapons and armor with the bones and metal of slain enemies.
In order to funnel all invaders to the battlefield of honor and glory, I wall off the entire edge of the map with retracted drawbridges except for a somewhat narrow path that leads right into my fortress. There is then nothing between my fortress and the invaders except for a large dwarven army. No fortifications, no traps, no engineering marvels. Just dwarven steel held in dwarven hands.
Its also a great way to manufacture artifacts. These aren't artifacts made by a mood, but instead artifacts that earn their status through endless battle, decorated with pages of bones and metal of slain enemies, and having earned their name through decades of endless warfare.