Free CNC Plasma Kerf Width & Offset Calculator
Determine cutting kerf width, CAM toolpath center offset, CW/CCW cut direction, pierce delay, and travel speed for precision CNC plasma cutting.
🔥 Material & Plasma Torch Setup
📊 Cut Width, Offset & CNC Feeds
Recommended Tools & Equipment
Tested hardware and components for high reliability
How CNC Plasma Kerf & Toolpath Offsets Work
Unlike a laser beam that cuts an ultra-thin 0.008" slit, an ionized plasma arc removes a substantial slot of melted metal known as the kerf width ($K_w$, typically 0.040" to 0.095"). If you program your CNC torch to travel directly along your CAD geometry line without offset compensation, your finished part will be undersized by the entire kerf width!
1. CAM Toolpath Center Offset
To produce a dimensionally accurate part, the center of the plasma torch nozzle must be offset by exactly half the kerf width:
- Outside Part Profiles: Offset the torch to the outside of the geometry line. Cut in a Clockwise (CW) direction.
- Inside Hole Cutouts: Offset the torch to the inside of the geometry line. Cut in a Counter-Clockwise (CCW) direction so the square edge stays on the part and the beveled taper is discarded with the scrap slug.
2. Pierce Height vs Cut Height
Never pierce metal at normal cutting height (0.060" / 1.5 mm). Liquid molten slag blows straight back up into the nozzle, clogging the orifice and destroying shields. Modern Torch Height Controllers (THC) pierce at 2× to 2.5× cut height (0.120" to 0.150"), dwelling for the pierce delay until the arc punches through, then plunging down to 0.060" before initiating travel.
Frequently Asked Questions
Why does my cut have heavy dross on the bottom of the plate?
High-speed dross (hard, bead-like) occurs when the torch moves too fast. Low-speed dross (thick, spongy, easily chipped off with a cold chisel) occurs when the torch moves too slowly, allowing excessive heat to puddle. Adjust travel speed in 5-10 IPM increments until dross minimizes.
How does torch height affect kerf width and bevel angle?
Running the torch too high expands the plasma cone, making the kerf wider and creating severe positive bevel taper. Running too close risks torch crashes and creates negative bevel (undercut). A calibrated Arc Voltage THC maintaining exact torch height is essential.
Can I cut 1/4" steel with 30A FineCut consumables?
No. FineCut consumables are engineered strictly for thin sheet metal (≤ 10-12 gauge / 3 mm). Attempting to cut 1/4" plate with 30A will cause the arc to lose penetration, spraying molten steel across the top of the plate and ruining the nozzle.
Why is air dryness critical for plasma kerf quality?
Moisture in compressed air causes green or black oxidization, erratic pilot arc ignition, wider kerf, and multiplies consumable wear by 5x. Always install a refrigerated air dryer or multi-stage desiccant filter with a coalescing oil separator.