The auto axe appears to be a modified industrial tool, strongly resembling a concrete saw or industrial grinder. The original blade seems to have been modified or replaced with a blade of a different kind, one with four roughly circular holes at the edges which creates four individual blades resembling axe blades.
The auto axe inflicts large amounts of damage with its sharp rotating blades, and functions like the Ripper. It can also be repaired using Rippers, including the unique Ripper Jack. Damage done by this weapon can be increased with the Auto Axpertperk which is available within The Pitt, after collecting 10 steel ingots from the steelyard.
This weapon does devastating damage, if you have any of the damage enhancing perks like Ghoul Ecology, Superior Defender, etc. these perks attributes are added per every "tick" of auto axe. With those perks, enemies can be sliced in a fraction of the time it took before.
When Pitt slaves are using this weapon for steel cutting, they can be seen pull starting it repeatedly, suggesting that the auto axe and its variants are gas powered. However, the player never has to do this, nor do non-player characters when its being used against another person as a weapon.
ps3pc Sometimes this weapon will disappear from first person perspective, but still function perfectly. If you then bring up the Pip-Boy while the weapon is equipped, the Pip-Boy will have disappeared from your arm also. This bug can be temporarily remedied by switching weapons or re-equipping the auto axe. You can also fix it by saving and loading the game. Making an attack with V.A.T.S. can also restore the weapon. [verified]
pc Sometimes the blade alone will disappear, but the weapon will still function perfectly. This can be remedied by switching weapons. [verified]
xbox360 Sometimes, out of V.A.T.S, the weapon may buckle, and instead of functioning with repeated damage (like the Ripper), it may function like a normal melee weapon and repeatedly hit only once, before pulling back and hitting again. This is easily fixable by simply stopping. [verified]
pc Sometimes the auto axe rotary blade will stop spinning in 1st person and will start spinning again in 3rd person. [verified]