CNC Plasma Pierce Height, Delay & Cut Speed

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How Pierce Height, Delay, Cut Height, and Speed Relate

A CNC plasma cycle is not one setting. It is a sequence:

1. Pierce height — torch parked above the plate so the transferred arc can punch a hole without the molten blowback eating the nozzle. Typical air-plasma mechanized pierce is about 0.15–0.25" above the top of the material, thicker plate toward the high end.
2. Pierce delay — how long the machine waits at that height after arc transfer before XY motion. Too short and you drag an incomplete hole; too long and you chew a crater and overheat the shield. Thin sheet is often 0.2–0.4 s; 1/2" can want a second or more.
3. Cut height — the standoff the THC (or a fixed Z) holds while cutting. Most shielded air-plasma stacks want about 0.06" on light plate and 0.08–0.12" as thickness and amps climb. Cut height is not pierce height. Dropping to cut height after the delay is the whole point of a two-height cycle.
4. Cut speed (IPM) — how fast the gantry tows the arc once the kerf is open. This is the number everyone argues about. It is also the last number you should chase. Speed that is “right” on a blown nozzle or a 0.20" cut height will still dross.

They trade. A slightly high cut height acts like a slower speed (wider kerf, more top rounding). A late delay on thin sheet acts like you started the cut already moving — the lead-in becomes a gouge. Stainless wants more delay than mild steel at the same thickness because the pierce is stickier. Aluminum spatters; that is why the calculator adds pierce height and delay on aluminum rather than copying the mild-steel row.

The calculator interpolates a mechanized air-plasma band for 40 / 45 / 65 / 85 / 105 A. It is a starting-point range. Consumable family (shielded vs FineCut), air PSI, and THC response will move every number. Your OEM cut chart for that exact stack still wins when you have it.

How to Dial In From the Calculator Starting Point

Do not change four knobs at once. Use the calculator output as the first coupon, then one variable per test cut on scrap of the same heat and thickness.

1. Load the calculator with material, thickness, and the amps the process is actually running (not the nameplate max). Write pierce height, delay, cut height, and the IPM band. PDF the cheat sheet if you want it on the console.
2. Pierce only. Command a pierce with XY locked. You want a through-hole, a round puddle, and a shield that is not painted with blowback. If the nozzle is cratered after two pierces, raise pierce height 0.02–0.04" or add delay — do not speed up the nest. Edge-start holes when the part allows it; a pierce in the middle of 1/2" is harder on consumables than an edge lead-in.
3. Delay. If the first 1/4" of motion is a skip or a blind trail, add 0.1–0.2 s. If the pierce hole is a volcano before the machine moves, subtract delay. Delay is time, not height.
4. Cut height / THC set point. A 0.06" shielded cut is the common air-plasma default. If the arc is wandering or the kerf is beveled the same direction on both sides of a part, height is off or the torch is not square — not IPM. Confirm Z with a feeler or the THC display, not by eyeballing the glow.
5. Speed last. Start at the midpoint of the calculator range. Soft, easy-to-chip bottom dross → increase IPM. Hard, welded-on bottom fin → decrease IPM a little and verify air. Top spatter with a good bottom → you are usually slow or low on amps. That fork is in CNC cut-quality troubleshooting.

Why These Are Not Handheld Settings

The existing Plasma Cutting Settings Guide and handheld calculator answer torch amps, travel speed, pierce time, and gas pressure for a human holding the handle. That operator can roll the wrist, drag a shield, and stretch a pierce by feel.

A table cannot. It only has Z height, a dwell, and a feed rate. Pierce “time” on a handheld chart is how long you linger before you pull; pierce delay on a CNC is a programmed wait at pierce height. Mixing those two cells is how shops blow a $12 nozzle on the first hole of a nest.

Stay in your lane: this cluster is gantry Z and IPM. Handheld amps/voltage/technique stay on the plasma-cutting pages. Comparison page if you run both in the same shop: CNC vs handheld.

What to Do With the Result on the Table

1. Enter the three inputs. Treat the IPM output as a range, not a single sacred number.
2. Put pierce height and delay in the CAM / THC pierce cycle. Put cut height in the THC set point. Put speed in the lead-in and contour feeds.
3. Run a pierce coupon and a 6" straight cut. Change one variable. Then nest.
4. If air PSI falls 20 seconds into a long contour, that is a compressor problem, not a cut-speed problem. See the plasma compressor guide.

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