Origin: There are two rival explanations as to the origin of this phrase. One is that it comes from the supposed habit of millers who checked that the stones used for grinding cereal weren’t overheating by putting their nose to the stone in order to smell any burning. The other is that it comes from the practice of knife grinders when sharpening blades to bend over the stone, or even to lie flat on their fronts, with their faces near the grindstone in order to hold the blades against the stone. (Source: The Phrase Finder)
All noses in my family seem to be intact and unblemished, but they did use this grindstone to sharpen knives, sickle sections and cutting tools. The pedal on each side kept the wheel turning while the operator sharpened the blades.
Today we have smaller scale versions of grindstones for sharpening paring knives and as we call them, toad stabbers (butcher knives). The concept is one in the same.
Until our next history lesson …