Slide 002: Cut Parameters — Speed, Amperage & Gas Selection

Slide Visual

Slide Overview

This slide teaches students how to select and balance the three primary plasma cutting parameters — amperage, speed, and gas type/pressure — for optimal cut quality. Understanding parameter relationships prevents poor cuts and excessive consumable wear.

Instruction Notes

The Parameter Triangle

Three parameters interact to determine cut quality: 1. Amperage — determines cutting energy (heat input) 2. Travel Speed — determines how long the arc dwells at each point 3. Gas Type/Pressure — determines arc shape, cooling, and chemical interaction

Changing one parameter requires adjusting at least one other to maintain cut quality.

Amperage Selection

Match amperage to material thickness:

Rule of thumb for mild steel with air: Maximum clean-cut thickness ≈ amperage × 0.006" (e.g., 65A × 0.006 = 0.39" ≈ ⅜")

Amperage	Clean Cut Capacity (Steel)	Sever Cut Capacity
25A	Up to 3/16"	¼"
45A	Up to 3/8"	½"
65A	Up to ½"	¾"
80A	Up to ¾"	1"

Clean cut: Good edge quality, minimal dross. Sever cut: Will get through but rough edge, heavy dross.

Travel Speed Optimization

The correct speed produces: - Slight trailing angle on drag lines (5°–15° from vertical) - Minimal dross on the bottom edge (and easily removable) - Clean, slightly rounded top edge without excessive melting - Narrow, consistent kerf

Speed adjustment guide:

Symptom	Diagnosis	Adjustment
Heavy dross, steep drag lines (>15°)	Too fast	Decrease speed 10-20%
Wide kerf, excessive top rounding, gouging on bottom	Too slow	Increase speed 15-25%
Arc extinguishes during cutting	Way too fast OR amperage too low	Decrease speed significantly or increase amperage
Clean cut with slight trailing drag lines	Correct speed	Maintain current parameters

Gas Selection Guide

Gas	Best For	Advantages	Disadvantages
Compressed Air	Mild steel, general purpose	Cheapest, most available	Oxidized edge on stainless/aluminum
Nitrogen (N₂)	Stainless steel, aluminum	Clean edges, no oxidation	Higher cost, requires cylinder
Oxygen (O₂)	Mild/carbon steel only	Fastest cuts, cleanest edges on steel	Damages stainless/aluminum, fire risk
Argon/Hydrogen (Ar/H₂)	Stainless steel, aluminum (thick)	Best quality on non-ferrous	Expensive, requires mixing

Pressure: Manufacturer-specified, typically 60-75 PSI for air plasma. Too low = poor cut, dross. Too high = blown-out arc, rapid consumable wear.

Air Quality Requirements

Contaminated air destroys consumables and cut quality: - Moisture: Causes electrode erosion, inconsistent arc. Use a refrigerated dryer or desiccant dryer - Oil: Contaminates the nozzle and electrode. Use an oil-removal filter - Particulates: Block gas passages. Use a 5-micron or finer inlet filter - Required: water separator + oil filter + particulate filter in series

Key Talking Points

1. Amperage determines capacity; speed determines quality; gas determines edge chemistry
2. Start with manufacturer's recommended parameters and adjust based on results
3. The drag line angle is the single best indicator of correct speed
4. Compressed air works for most makerspace applications — N₂ is a quality upgrade for stainless/aluminum
5. Dirty air is the #1 consumable killer — maintain filtration

Learning Objectives (Concept Check)

• [ ] Select appropriate amperage for 3 different material thicknesses
• [ ] Diagnose cut quality issues from drag line angle and dross characteristics
• [ ] Choose the correct cutting gas for mild steel, stainless steel, and aluminum

---

Last Updated: 2026-03-19