Nose to the grindstone

Photo of someone with their nose to a grindstone
The phrase nose to the grindstone means to work hard.
It originates from the literal hard work of sharpening tools on a grinding wheel, where workers who were sharpening knives had to bend close to the stone to work.
Similar idioms are back to the grindstone or the daily grind and are all variations on this idiom.

Well, lunch is over, better go back and put my nose to the grindstone.