The sharpening angle, drawn
The angle you sharpen at decides how easily a knife enters food and how long its edge survives. Move the slider. The drawing shows the edge in cross-section, enlarged, and the height to hold the spine above the stone.
Contents
How to read it
The angle is given per side. A knife sharpened at 15° on each side has a 30° edge in total. The narrower the wedge, the less force it takes to part the food. The wider the wedge, the more steel supports the edge and the longer it resists rolling and chipping.
The right angle depends on the core steel. A hard core, 60 HRC and above, can carry 12 to 15° per side. A softer blade, 56 to 58 HRC, is better at 18 to 20°. A cleaver that meets bone wants 22° or more. The guide to core steels gives the usual hardness of each steel.
Holding the angle on a stone
Nobody measures degrees by eye. Measure height instead. The tool gives the gap between the spine and the stone for a blade 45 mm tall, the usual height of a chef knife at the heel. At 15° that is about 12 mm, roughly two stacked coins under the spine. Find the height, lock your wrist, and keep it there for every stroke.
Sharpen one side until you feel a burr along the whole edge, a thin wire of steel you can catch with a fingertip from the other side. Switch sides, repeat, then finish with light alternating strokes on a finer stone.
Keep the angle the knife came with
Unless you have a reason to change it, sharpen at the angle the maker ground. Most damascus kitchen knives with a core at 60 HRC or more leave the workshop at around 15° per side. If you do not know, colour the edge bevel with a marker, make one light stroke, and see where the ink is gone: at the very edge your angle is too high, at the shoulder it is too low. Next, see how the three cutting motions use the edge or how to choose a chef knife.