What a plasma cut chart actually encodes

Two plasma tables can run the same machine, the same torch and the same sheet and produce different parts, because the part quality does not live in the hardware. It lives in a table of numbers: for each material at each thickness, how fast to move, how long to wait before moving and how wide the cut actually is. That table is the cut chart, and most of the craft knowledge in a profiling shop is really a set of amendments to it.

Three numbers per row

A working chart holds at least three values per material and thickness. Feed rate, in millimetres per minute, is how fast the torch travels while cutting: too fast and the arc lags and leaves an unfinished kerf with heavy bevel, too slow and the arc wanders, the kerf widens and low speed dross builds on the bottom edge. Pierce time, in seconds, is how long the torch dwells after firing before it starts to move, while the arc blows through the sheet. Kerf, in millimetres, is the width of metal the arc removes, and it is the one that decides whether the part measures right.

Kerf is half a number

The arc removes a slot of metal, not a line, so a torch driven along the drawn outline produces a part undersize by half the kerf on every edge. The controller therefore offsets the toolpath outward by half the kerf for outside profiles and inward for holes, which is why kerf appears in the chart as a full width but acts in the geometry as a half. It also explains two familiar shop truths: a hole always suffers more than an outside edge, because the compensation curvature is against it, and a kerf value that is 0.4mm out puts every edge 0.2mm out, so a width measured across two opposite edges is 0.4mm out.

Pierce is where the failures cluster

Piercing is the violent part of the cycle. The arc has to blow molten metal back out of the hole it is making, so the machine pierces above the cut height, dwells for the pierce time, then drops and goes. Too short a dwell and the torch sets off before the sheet is through, ploughing a furrow instead of a cut. Too long wastes consumables and heat. Thick plate moves the problem sideways: the pierce happens away from the contour on a lead-in, so the crater the pierce leaves sits in scrap rather than in the part's edge.

Whose numbers are they?

Manufacturers publish starting charts for their torch at each amperage, and they are exactly that, starting points. Every table settles into its own figures as consumables wear, as the shop learns what its air supply and its steel actually do, and as operators trade a little speed for a cleaner edge on the work they see most. The practical failure is that these amendments live in one operator's head or a notebook by the console, so the chart the software uses and the chart the shop believes drift apart, and every part cut in the gap between them carries the error.