Scallops
Scallops turns up in 2 fields: gears, lighting. Here is what it means to the people in each one.
Scallops in gears
Shop word for the small ridges a hob leaves across and along each tooth flank, visible as a fine texture.
The faceted surface left by hobbing: generating flats along the profile from the finite number of hob gashes, and feed marks along the face from the axial feed per revolution. Their size depends on the number of gashes, the number of starts and the feed rate, and they are visible in profile and lead traces as small regular waves. Finer feeds or a finishing process such as shaving or grinding remove them.
"Scallops on the flank are too coarse, drop the feed for the finish pass or the lead trace will look like a saw blade."
Scallops in lighting
The arched pattern of light and shadow that downlights draw on a wall when mounted close to it.
When a downlight's cone of light hits a nearby wall, the top edge of the beam forms a bright arch with a dark area between each fixture, giving a row of scallops. Designers sometimes use them deliberately as a rhythm along a corridor, but more often they are a sign the fixtures are too close to the wall or have the wrong optic. Moving fixtures out, using wall wash trims or tightening spacing reduces them.
"Look at the scallops on the hallway wall, those cans are 12 inches off the wall, we drew them at 30."