Cutting Tolerances

Modern flamecutting machines are CNC controlled machine tools that will trace the programmed path with a very high degree of accuracy, generally to within a few thousandths of an inch. The cutting oxygen stream from the cutting tip creates a consistent and uniform kerf. Why, then, does flamecutting require tolerances like these?

The reason for these more generous tolerances is that the intense heat of the burning process causes the steel along the cut to expand, creating powerful stresses in the plate. Due to the destructive nature of flamecutting, the plate cannot be fixtured, and so these stresses will cause the plate to shift or “walk” during the cutting process.

Beyond this dimensional tolerance, there is also a need to account for how the cut will deviate from square. Generally, a flamecut edge can be expected to be perpendicular within 1-1/2 degrees to the top surface of the plate. This has a minimal affect on lighter plate, but on heavy plate it can mean a possible deviation that is significant. In inches, the edge can be out of square: