Stop-off
Stop-off turns up in 2 fields: heat treating, metallurgy. Here is what it means to the people in each one.
Stop-off in heat treating
A paint, paste or plating applied to areas of a part that must not carburize or nitride.
Masking used for selective case hardening. Copper plating roughly 0.013 to 0.025 mm thick is the standard barrier against carbon, while ceramic or boron-based paints and tin-based pastes are brushed on for carburizing and nitriding. Threads, bores that will be machined later and weld zones are typical stop-off areas. Coverage must be complete and dry, because a pinhole leaves a hard spot right where machining or welding comes next.
"Paint stop-off on the threads, they have to stay soft enough to chase after carburize."
Stop off in metallurgy
To block a portion of a mold cavity with sand so that part of the pattern does not cast.
Stopping off is a manual molding technique used to cast a shorter or modified version of an existing pattern without physically cutting the pattern itself. The molder packs green sand into the unwanted section of the mold cavity after the pattern is drawn, creating a new boundary for the molten metal. This saves the cost of building a custom pattern for a one-off variation.
"Stop off the last six inches of that pipe pattern so we can pour a custom length for the repair job."