Slide 003: Kerf Compensation, HAZ & Part Layout¶
Slide Visual¶
Slide Overview¶
This slide covers the practical considerations of kerf compensation in part programming, the heat-affected zone and its impact on downstream fabrication, and efficient part layout (nesting) for material optimization.
Instruction Notes¶
Kerf Compensation¶
The plasma arc removes material — the kerf width (typically 0.05"–0.12") means the actual cut is wider than an infinitely thin line. Without compensation, parts will be undersized by approximately half the kerf width on each side.
Kerf compensation rules: - Outside profiles: Offset the toolpath outside the part by half the kerf width - Inside profiles (holes): Offset the toolpath inside the hole by half the kerf width - Most CNC plasma CAM software handles this automatically — specify kerf width in the tool settings - Measure actual kerf on a test cut and enter the measured value, not a theoretical one
Typical kerf widths:
| Amperage | Mild Steel Kerf | Stainless Kerf | Aluminum Kerf |
|---|---|---|---|
| 25-30A | 0.050"–0.060" | 0.055"–0.065" | 0.055"–0.065" |
| 40-50A | 0.065"–0.080" | 0.070"–0.085" | 0.070"–0.085" |
| 65-80A | 0.080"–0.110" | 0.090"–0.120" | 0.090"–0.120" |
Bevel Angle & Cut Direction¶
The plasma arc swirl creates a bevel (1°–5° off perpendicular) with the squarer edge on the RIGHT side of the cut direction (for most machines with clockwise gas swirl).
Programming rule: - Outside profiles: Cut CLOCKWISE — good edge faces the part - Inside profiles (holes): Cut COUNTER-CLOCKWISE — good edge faces the part - This convention applies to most machines — verify with a test cut on your specific system
Heat-Affected Zone (HAZ)¶
The HAZ is the region adjacent to the cut where the base metal was heated enough to alter its microstructure but not melted:
| Material | Typical HAZ Width | Effect |
|---|---|---|
| Mild steel | 0.020"–0.060" | Increased hardness, slight embrittlement |
| Stainless steel | 0.030"–0.100" | Carbide precipitation (sensitization), reduced corrosion resistance |
| Aluminum | 0.040"–0.120" | Overaging (softening) in heat-treatable alloys |
HAZ Implications: - Welding near a plasma-cut edge may require preheat or post-weld heat treatment - Bending near the cut edge may crack through the HAZ — leave 1× material thickness margin - For critical applications, machine 0.030"–0.060" off the plasma-cut edge to remove the HAZ
Part Layout & Nesting¶
Efficient nesting reduces material waste: - Minimum part spacing: Kerf width + 0.25" (for thin material) to kerf + 0.50" (for thick material) - Edge margin: Minimum 0.50" from material edge to nearest cut line — prevents edge warping - Common line cutting: Adjacent parts share a cut line — saves one kerf width per shared edge. Requires careful programming to avoid double-cutting - Lead-in position: Place lead-ins (pierce points) on the scrap side or in non-critical areas of the part - Cut sequence: Cut interior features (holes) before exterior profiles — keeps the part fixtured longer - Skeleton tabs: Leave small connections between nested parts and the skeleton to prevent parts from tipping into the water table
Key Talking Points¶
- Kerf compensation is essential for dimensional accuracy — always measure actual kerf, do not guess
- Cut direction (CW vs. CCW) determines which side gets the square edge
- The HAZ affects downstream fabrication — account for it when designing parts
- Efficient nesting can save 15-30% material over naive layouts
- Always cut holes before outside profiles to maintain material rigidity
Learning Objectives (Concept Check)¶
- [ ] Calculate kerf compensation for inside and outside profiles
- [ ] Specify correct cut direction for parts and holes based on bevel angle
- [ ] Describe 3 effects of the HAZ on downstream fabrication
- [ ] Apply basic nesting principles to a multi-part layout
Last Updated: 2026-03-19