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About the plasma and steel glossary

Plain-English definitions of the words you will meet in plasma cutting, nesting and steelwork.

Air plasma: Plasma cutting that uses compressed air as the plasma gas. Cheap to run and ideal for mild steel up to about 25 mm.
Amperage: The current the plasma torch runs at. Higher amps cut thicker plate and faster, with a wider kerf.
Arc voltage: The voltage across the plasma arc. Torch height controllers read it to keep the torch at the right height.
Arc-on time: The time the torch is actually cutting, as opposed to moving between parts or piercing.
As cut: Parts supplied straight off the table, with no deburring or coating.
Bend allowance: The length of material inside a bend, used to work out the flat blank length of a folded part.
Bend deduction: How much to take off the sum of the outside flange lengths to get the flat blank length.
Bevel: A slight angle on a cut edge. Plasma leaves 1 to 3 degrees of bevel, more on thick plate.
Bolt circle: See PCD.
Bridge: A small uncut tab that holds a part in the sheet until it is knocked out.
Burr: A sharp raised edge left on a cut or drilled edge, removed by deburring.
CAD: Computer-aided design: software such as AutoCAD, SolidWorks or Fusion used to draw parts.
CAM: Computer-aided manufacturing: software that turns drawings into the torch paths a machine follows.
Chamfer: A flat, angled corner cut off a plate, often to clear a weld or root radius.
Clearance hole: A hole slightly bigger than the bolt so it passes through freely. Sizes are set by ISO 273.
CNC: Computer numerical control: a machine that moves under the control of a program.
Common-line cutting: Placing parts so they share one cut edge, saving cut time and material.
Contour: A single closed outline in a drawing: the outside of a part or one of its holes.
Corten: Weathering steel that forms a stable rust-coloured layer instead of corroding further.
Cut chart: A table of speed, amps, height and kerf for each material and thickness.
Cut length: The total distance the torch cuts for a part: the outline plus every hole.
Cut path: The route the torch follows, offset by half the kerf so parts come out at drawing size.
Cutting table: The bed the plate sits on while it is cut. Ours take sheets up to 3000 x 1500 mm.
Deburring: Removing burrs and dross from cut edges so parts are safe to handle.
Density: Mass per unit volume. Steel is about 7,850 kg/m3; aluminium about 2,700 kg/m3.
Dross: Re-solidified metal stuck to the bottom edge of a plasma cut. Good settings keep it light.
DWF: Design Web Format, an Autodesk format for sharing drawings. We read the DWFx version.
DWG: AutoCAD's native drawing format.
DXF: Drawing Exchange Format, the most common way to send flat 2D parts for cutting.
Edge distance: The distance from the centre of a hole to the edge of the plate. Too small and the edge can tear.
EIA code: The common G-code style used by most plasma controllers: G00, G01, G02, G03 and M codes.
End distance: The distance from a hole centre to the end of the plate in the direction of the load.
ESSI: An older numeric program format for profile cutting machines, still read by many controllers.
Etching: A low-power mark on the plate surface, used for part numbers, bend lines or drill centres.
Fangling: A Chinese controller brand found on many gantry plasma tables. Our default post-processor.
Fine cut: Consumables that give a narrower, sharper arc for thin plate, at a lower speed.
Flange: A flat ring with a bore and bolt holes, used to join pipes or fix a shaft.
Flat blank: The flat shape cut from the sheet before it is folded.
G-code: The program language that tells a CNC machine where to move and when to start and stop cutting.
Gantry: The bridge that carries the torch across the cutting table.
Gauge: An old numbering system for sheet thickness. The same number means different thicknesses in different metals.
Grade: The specification of a steel, such as S275 or S355, which sets its strength.
Grain direction: The rolling direction of a sheet. It matters for brushed finishes and tight bends.
Gusset: A triangular plate that stiffens a joint between two members.
Hardox: A brand of wear-resistant steel plate used in buckets, chutes and liners.
Holding-down bolt: A bolt cast into concrete that fixes a column base plate to the foundation.
Hot-rolled: Steel rolled while red hot, with a grey mill-scale surface. Most structural plate is hot-rolled.
IGES: An older 3D exchange format. We take the flat face of a plate from it.
Inside radius: The radius on the inside of a bend, set by the press brake tooling.
ISO 273: The standard that sets close, normal and loose clearance hole sizes for metric bolts.
K-factor: Where the neutral axis sits inside a bend, as a fraction of thickness. Usually 0.3 to 0.5.
Kerf: The width of material the cut removes. Plasma kerf is about 1.2 to 3.5 mm depending on thickness.
Kerf compensation: Offsetting the torch path by half the kerf so parts come out at the drawn size.
Lead-in: A short move from the pierce point onto the cut line, so the pierce mark stays off the part.
Lead-out: A short move off the cut line at the end of a contour, giving a clean finish.
Lifting lug: A plate with a pin hole welded to a load so it can be lifted with a shackle.
Mach3: PC-based machine control software used on many hobby and light industrial tables.
Margin: The strip left unused around the edge of a sheet.
Mark: The part number given to each different part. Identical parts always share one mark.
Micro-joint: See bridge.
Mild steel: Low-carbon structural steel such as S275 or S355. The material we cut most.
Mill certificate: The steelmaker's test certificate showing the grade, chemistry and strength of a batch.
Mill scale: The dark oxide layer on hot-rolled steel.
Minimum hole: The smallest hole plasma cuts cleanly, roughly equal to the plate thickness and never under 3 mm.
Mirror: Flipping a part so a left-hand and a right-hand version can be cut from one drawing.
NC file: The numerical control program a cutting machine runs.
Nesting: Arranging parts on a sheet to use as much of it as possible.
Offcut: The usable piece of sheet left over after cutting.
Open contour: An outline that does not close back on itself. It cannot be cut as a part until it is closed.
Part-in-part: Nesting small parts inside the holes of larger parts to save material.
PCD: Pitch circle diameter: the circle through the centres of a ring of bolt holes.
Pierce: Punching through the plate with the arc before a cut starts. Each outline and hole needs one.
Pierce delay: How long the torch pauses while piercing before it moves. Longer for thicker plate.
Pierce height: The higher torch position used while piercing, to protect the nozzle from splash.
Pitch: The centre-to-centre spacing of bolt holes in a line.
Plasma: Ionised gas hot enough to melt steel, blown through the cut by the gas flow.
Plate: Flat steel, usually 3 mm thick or more. Thinner flat material is called sheet.
Post-processor: Software that writes the cut path in the exact dialect a particular controller understands.
Press brake: The machine that folds plate along a straight line.
Primer: A first coat of paint that protects steel from rust and gives a key for top coats.
Profile: The outline shape of a cut part.
Rapid: A fast move with the torch off, between one cut and the next.
RHS: Rectangular hollow section: a rectangular steel tube.
Root radius: The curved fillet where the web of a beam meets its flange.
S275: A common structural steel grade with a yield strength of 275 N/mm2.
S355: A stronger structural steel grade with a yield strength of 355 N/mm2.
Sheet: Flat metal under about 3 mm thick.
SHS: Square hollow section: a square steel tube.
Skeleton: The web of sheet left after all the parts have been cut out.
Slot: An elongated hole that allows a bolt to be adjusted on site.
Spatter: Molten droplets thrown out during piercing, which can stick to the plate or the torch.
Stainless steel: Steel with chromium added so it resists corrosion. 304 for general use, 316 near the sea.
Starfire: A controller brand used on portable and light gantry plasma tables.
STEP: The standard 3D model exchange format. We take the flat face of a plate from it.
Stiffener: A plate welded into a beam to stop the web or flange buckling under load.
Tap drill: The drill size for a hole that will be threaded with a tap.
Taper: A hole slightly larger on top than underneath, normal for plasma in thick plate.
Torch height control: A system that keeps the torch at the right height above the plate as it cuts.
True-shape nesting: Nesting parts by their real outlines rather than their bounding boxes, so they interlock.
UB: Universal beam: an I-shaped hot-rolled steel section, deeper than it is wide.
UC: Universal column: an H-shaped hot-rolled steel section, about as wide as it is deep.
Utilisation: The percentage of the sheet area that ends up as parts.
Weld prep: A bevel or chamfer cut on an edge so a weld can penetrate fully.
Yield: How many parts you get from a sheet.
Yield strength: The stress at which steel starts to stretch permanently.

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