By repairing sledgehammers (the vanilla way) you can dupe sledgehammers to your heart's content. This is problematic with any mod that has un-crafting or tool smelting into ingots/molten metal.

Mod list:
Astral sorcery (+ lib)
Immersive Engineering
Baubles
End:Reborn

Steps to reproduce:
Crafting screenshot 1
Crafting screenshot 2
Crafting screenshot 3

I`ll try to fix this in the next update. Thanks for feedback