The Knife’s Edge
By J. Bayer
The old man bent lower so he might hear his young apprentice’s question.
“Couldn’t we sharpen the blade on the grinding wheel?”
“Indeed we could,” said the old man, “but that would result in a hollow grind and this iron blade would never hold its edge.”
To prove his point, the old man beckoned his apprentice to a draw knife he’d been sharpening earlier. He picked it up and pointed to the distinctive concave profile on the knife’s edge. “This is a steel blade and the tool is used for shaving wood, not for chopping. A hollow grind is good for draw knives, scorps, and spoke shaves because they’re slicing tools. Chopping blades must be sharpened on a flat stone, not a wheel.”
“It’s much the same for saw blades,” the old man continued, and he retrieved two handsaws from pegs on the wall. “See here, this saw is used for cross-cutting wood. The saw’s teeth are filed straight across because in cross-cutting the saw is really chipping through the wood when it cuts.” The old man put down the cross-cut saw and held the ripping saw for the boy to see. “Notice how the teeth on this saw are filed at alternating angles? This is so the saw can slice with the grain of the wood.”
“But why are the saw’s teeth bent outward in opposite directions?” asked the apprentice.
“It’s called the kerf,” said the old man. “By setting the teeth like that, the wood won’t close up on the saw – but we’ll talk about kerfs, setting teeth, and fleem another time.”
The old man returned to sharpening the large blade and the apprentice watched his master’s nimble strokes in silence.
At length, the old man looked up with a satisfied grin. “I think this blade is ready for Doctor Guillotine.”