Build a CNC Plasma Cutting Table

The Wolfpawn 4040 Pro and most desktop CNC routers on this site handle wood, plastics, and thin aluminum, and our handheld plasma cutting guide covers freehand work with mild steel plate. What neither one does is combine the two: a CNC-driven plasma cutter that can cut clean, repeatable shapes out of 3/16" to 3/8" steel or aluminum from a DXF file, unattended, at a fraction of the time a handheld torch and a steady hand would take. This project walks through building a dedicated CNC plasma table from an aluminum extrusion frame, a plasma-rated XY gantry, and torch height control (THC) — the one piece of this build that has no equivalent on a router or laser and that most first-time builders underestimate.

Why a Plasma Table Is a Different Machine, Not a Router With a Torch Bolted On

It's tempting to look at this as "take my CNC router build and swap the spindle for a torch," but a few things make plasma cutting mechanically and electrically distinct enough to warrant a purpose-built machine:

• Z-axis tracking, not fixed height. Steel plate is never perfectly flat, and plasma cut quality is extremely sensitive to standoff distance — a router bit doesn't care if your stock has a 1mm bow across a sheet, but a plasma torch running 0.5mm too high or low produces visibly worse cuts or blows through consumables early. A THC unit continuously reads arc voltage and adjusts Z in real time to hold standoff distance, and it is not optional for anything beyond the simplest flat, pre-flattened stock.
• Electrical noise. A plasma arc is one of the noisiest electrical events you'll run in a home shop — it radiates broadband RF and injects noise onto anything nearby, including your controller's step/dir signals if wiring isn't shielded and grounded properly. Router and laser controllers can often get away with sloppy wiring practices that will cause a plasma table to lose steps or false-trigger limit switches.
• Water or downdraft table underneath. Plasma cutting throws molten slag and UV-bright light downward continuously. A water table (slats submerged an inch or two below the cut surface) is the standard home-shop solution — it quenches slag, suppresses fumes and noise significantly, and reduces reflected UV. A dry downdraft table with aggressive extraction is the alternative where water isn't practical, but it requires a much stronger fume extraction setup than woodworking dust collection.
• Software and post-processor differences. Plasma-specific CAM (SheetCam, or plasma post-processors in Fusion 360/VCarve) needs to handle lead-in/lead-out arcs, kerf compensation for a much wider kerf than a router bit or laser, and pierce delay — cutting straight into the plate at full power without a pierce sequence will blow the tip prematurely.

Frame and Motion System

The frame follows the same basic playbook as our DIY CNC router build — 2040 or 4040 aluminum extrusion, gantry-style XY with a fixed bed, NEMA 23 steppers on the gantry axes for the torque needed to move a heavier Z assembly reliably. A few plasma-specific differences matter:

ComponentRouter BuildPlasma Build Z-axisFixed offset, set once per job with a touch probeFloating head design + THC controller adjusting continuously during the cut BedSpoilboard, vacuum, or T-trackSlatted water table or downdraft table — never a solid spoilboard Cable managementStandard drag chainShielded drag chain with plasma torch leads and control wiring in separate, grounded chains — do not run torch leads and stepper wiring in the same unshielded bundle Rail exposureEnclosed or open, doesn't matter muchLinear rails need covers or a design that keeps slag and water spray off the bearings — exposed rails on a plasma table corrode and seize quickly without protection

Size the table for the material you'll actually run — a 2'x2' or 2'x4' table covers the vast majority of hobby sheet metal work (brackets, signs, small parts) without the cost and floor space of a full 4'x8' table. Keep the gantry rigid; unlike a router, plasma cutting doesn't put much lateral force into the material, but a wobbly gantry still shows up as wavy cut edges at speed.

Torch Height Control (THC)

This is the component that separates a working plasma table from a frustrating one. An arc voltage THC unit (Proma THC, CandCNC, or one of the open-source options that pairs with LinuxCNC or Mach3/Mach4) reads the voltage across the arc, compares it to a target voltage for your amperage and material, and drives the Z-axis up or down to hold that voltage — which corresponds to holding a consistent standoff height. Key setup points:

1. Initial height sensing (IHS). Before every pierce, the machine needs to find the plate surface. Most builds use a floating head with a switch, or a dedicated ohmic/capacitive sensor that detects contact or proximity to the plate — this happens automatically at the start of every cut path.
2. Arc voltage feedback wiring. The THC needs an isolated voltage divider reading directly off the torch and work lead, rated for the full open-circuit voltage of your plasma supply (200V+ on many hobby units). This is high voltage — treat this wiring with the same respect as mains work, and use a THC unit's factory voltage divider board rather than building your own unless you specifically know what you're doing here.
3. THC hold-off / lock height. THC should disable itself for the first portion of a cut (while the arc is still stabilizing after pierce) and around corners, where a momentary voltage dip from decelerating would otherwise cause the head to plunge into the plate. Every THC controller has a setting for this — leaving it at a default without understanding it is the single most common cause of a torch diving into the workpiece mid-cut.
4. Kerf compensation. Plasma kerf is typically 0.04"–0.08" depending on amperage and consumables — dial this into your CAM post-processor's kerf width setting so cut parts come out to size rather than consistently undersized.

Controller and CAM Software

LinuxCNC on a dedicated PC (or a Raspberry Pi running LinuxCNC with a Mesa Ethernet card, as covered elsewhere on this site) is the most common open path for plasma, with mature THC component support built in. Mach3/Mach4 with a THC-capable breakout board (see our Mach3/Mach4 setup guide) is the other common route, especially for builders coming from a Windows-based router setup. Either way, avoid running plasma off a bare GRBL board without THC support — GRBL has no native arc voltage feedback loop, and running plasma without real-time Z tracking limits you to perfectly flat stock and short cuts before standoff drifts out of range.

For CAM, SheetCam is the de facto standard for hobby plasma — it handles lead-ins, pierce points, and plasma-specific cut ordering (cutting internal features before the outer profile, so the part doesn't shift once it's freed). Fusion 360 and VCarve both have plasma post-processors as well if you're already working in one of those from CNC router work.

Safety

Plasma cutting combines several hazards that don't stack the same way on a router or laser table, and this build deserves a genuinely cautious approach:

• UV and IR radiation. The arc produces intense UV, comparable to arc welding — auto-darkening welding-rated eye protection (not standard safety glasses) is required for anyone in the room during a cut, and skin should be covered the same way you would for welding.
• Electrical hazard. Plasma power supplies run high open-circuit voltage. Keep the enclosure closed, don't work on torch or voltage divider wiring with the unit powered, and treat every lead as live until you've verified it isn't.
• Fume extraction. Cutting coated, galvanized, or painted steel releases hazardous fumes (galvanized steel specifically releases zinc oxide fumes that cause metal fume fever) — a water table suppresses a significant portion of airborne particulate, but you still need real extraction pulling fumes away from your breathing zone, and galvanized/coated material needs even more caution or should be avoided entirely in a home shop without a proper fume hood.
• Fire and slag. Molten slag lands wherever the water table doesn't catch it — clear the area of anything flammable, and keep a fire extinguisher rated for metal fires within reach.
• Noise. A plasma arc is loud enough to warrant hearing protection during cuts, especially with a dry downdraft table rather than a water table to dampen it.

First Cuts and Dialing In

Start with mild steel at a moderate amperage your plasma supply is rated for comfortably (running near the top of a unit's duty cycle rating on every cut shortens consumable and torch life fast). Cut a simple test piece — a 2" square with a small hole — and check for consistent kerf width, minimal dross (the resolidified slag that clings to the underside of a cut edge; excessive dross means either travel speed is too slow, amperage is too high, or standoff is off), and a square, not beveled, cut edge. Most controller software has a material library or lets you save cut parameters (amperage, speed, pierce delay, THC target voltage) per material and thickness, the same way LightBurn or an FDM slicer saves per-material profiles — build that library out as you dial in each thickness you'll use regularly.

A CNC plasma table earns its keep fast once it's dialed in — brackets, name plates, gears, enclosures, and structural steel parts that would otherwise mean a trip to a metal fab shop become an evening project. It's a genuinely different machine from a router or laser in how it demands to be wired and tuned, but the payoff is cutting real structural steel and aluminum plate on a bench you built yourself.