A hot crack—often referred to technically as solidification cracking or thermal stress cracking—occurs when metal expands and contracts rapidly during CNC thermal cutting. While SheetCam itself is software and does not physically cut the metal, specific toolpath configurations, lead-in selections, and speed settings generated within SheetCam directly influence the thermal profile of the cut.
Impurities in plasma air (moisture/oil) alter arc chemistry and increase heat. Install high-efficiency air dryers and filters.
In SheetCam, configure an "Overcut" (e.g., 1mm to 2mm). This allows the torch to travel slightly past the start point before shutting off, preventing a heavy thermal dump or "divot" at the closing point of the geometry.
What and type (steel, aluminum, etc.) are you cutting? What plasma cutter model and amperage are you using?
Use the exact feed rate recommended by your plasma or laser manufacturer for your specific material thickness. sheetcam hot crack
This technique effectively "scoops" the molten metal out of the way rather than blowing it up into the torch, dramatically extending consumable life and ensuring a clean, crack-free start on thick plates. While standard on many modern systems, you can often simulate this in SheetCam's post-processor by adjusting the pierce delay and lead-in motion for a "wiggle pierce" to blow away the slag.
Avoid straight-line lead-ins. An arc lead-in introduces the heat gradually and transitions smoothly into the cut path, distributing thermal stress.
SheetCam is considered a low-cost professional tool. A perpetual license typically costs around (or approximately €239 depending on the vendor). Sheetcam license or alternative - Problems and questions
By adjusting these parameters in SheetCam, you shift the thermal stresses of piercing and extinguishing into the scrap material, leaving your final part clean, precise, and structurally sound. Share public link Install high-efficiency air dryers and filters
I can provide the exact SheetCam parameters for your specific setup. Share public link
Ensure the feed rate configured in SheetCam matches the exact material thickness and amperage.
If you have optimized your SheetCam settings and are still experiencing hot cracking, the issue may stem from your physical setup:
To prevent the "blow-out" or cracking that occurs at the start of a cut, SheetCam allows for customized lead-ins (arc, tangent, or perpendicular). By piercing the material in a waste area and moving into the path, the initial thermal shock—the most likely moment for a hot crack to initiate—is kept away from the finished edge. Overcut and Cooling Pauses: What and type (steel, aluminum, etc
One of the most common causes of a hot crack is cutting internal holes. If you cut a hole in a single continuous motion, the heat concentrates in the center of the part, often causing the surrounding metal to warp.
You can edit your specific post processor in SheetCam to include a brief pause or to command the torch off slightly before the motion stops. Alternatively, check your CNC control software (like Mach3, Mach4, or FireControl) for settings related to Torch Off Delay and ensure it is set to 0 seconds so the software doesn't force an artificial dwell at the end of the cut. Recommended SheetCam Settings Quick-Reference Material Thickness Recommended Overcut Lead-Out Type Lead-Out Length Thin (under 1/8" / 3mm) 0.040" (1.0mm) 0.050" (1.2mm) Medium (1/8" to 1/4") 0.080" (2.0mm) Arc or Line 0.080" (2.0mm) Thick (Over 1/4" / 6mm) 0.120" (3.0mm) 0.120" (3.0mm) Conclusion
To minimize the occurrence of hot cracks in Sheetcam: