I Hacked My Plasma Table with a Skateboard

Tech / Product Concept Summary

• Goal: Turn a plasma table into a tube notching / stick-making machine using a skateboard wheel assembly as a low-cost rolling/positioning mechanism.
• Approach: Build a simple mechanical fixture that:
  • Attaches to the plasma table gantry.
  • Holds and pivots a tube cutter / notching wheel mechanism so tubes can be loaded/unloaded.
  • Uses a spring clamp to keep the tube located while cutting.
• Core promise: “Convert pretty much any plasma table into a tube notcher” by combining basic CAD modeling, DXF workflows, and plasma CAM programming.

Major Technical Steps / “How-To” Elements

1) Measurement & Alignment

To align the cut correctly, you need the tube’s centerline lined up with the plasma nozzle center.

• Key measurements:
  • Distance from gantry face to nozzle center (computed via scribes/calipers), resulting in 6.25 in.
  • Gantry thickness and other offsets.
• No expensive scanning: Uses a scribing line method to infer nozzle position without costly measurement tools.

2) Simple CAD Modeling (Quick Proof-of-Concept)

A quick proof-of-concept focuses on an assembly that can be fabricated and tested.

• Includes:
  • Wheels (skateboard parts)
  • Tube representation (using tube diameter in the model)
  • Gantry mount
  • Pivoting upper section actuated by a spring
• Workflow:
  • Export parts for fabrication as DXF
  • Use nesting for cutting

3) Fabrication / Fit-Up Considerations

After plasma cutting the fixture parts, the build requires cleanup and fit tuning.

• Post-cut cleanup:
  • Clean up slots/holes using a cut-off wheel and carbide chasing to ensure proper fit.
• Welding:
  • Weld with 309 stainless filler for frame/fixture materials.
• Accuracy limits:
  • Plasma/air-plasma cutting isn’t as precise as laser, so manual cleanup is expected.

4) Tube Notch Geometry Workflow Using CAD (Onshape Focus)

A CAD workflow generates notch cut profiles that can be flattened into sheet-metal style outputs for CAM.

• Tutorial workflow:
  1. Sketch notch positions:
     • Straight notch
     • Angled notch
     • Miter concept
  2. Use Onshape functions:
     • Frame (tube element modeling)
     • Frame trim (create notch openings)
     • Convert notch geometry into a sheet metal model
  3. Flattening step:
     • Produces cut profiles that map to plasma table operations.
• Tube specifics mentioned:
  • Example tube modeled/cut as 1.75 in OD with 0.083 wall (Chromoly)
• Geometry rule-of-thumb hint:
  • Mentions classic guideline: 1/3 tube diameter ≈ throat depth
  • Uses fillets based on that relationship for clearance.

5) DXF / CAM / SheetCam Programming

The notch profiles are exported and converted into toolpaths in SheetCam.

• Workflow:
  • Export notch profiles as DXF
  • Process in SheetCam
• Critical CAM notes:
  • Orientation matters:
    • X axis rolls tube
    • Y axis moves along tube length
  • Ensure there are no extra “S lines”—only the notch profile is intended to cut.
  • Add/adjust:
    • Lead-in / lead-out
    • Overcut (tuned based on cut success)
• Troubleshooting toolpaths:
  • Switch between fine-cut consumables vs regular consumables
  • Change amperage and speed
  • Use lead-in on open profiles when needed
  • Adjust tangent vs perpendicular lead-in to improve alignment/cutting behavior

6) Mechanical Tuning During Testing

Testing focuses on real-world behavior of the tube and fixture stability.

• Watch for issues like:
  • Tube length affecting Y positioning
  • Plate cleanliness being important: trash on plate can cause chatter and knock the tube around
  • Spring rate / pivot fit adjustments (two spring sizes considered)
• Results:
  • Proof-of-concept is positive: notches mostly fit
  • Throat depth / clearance is “not quite enough,” suggesting model refinement is needed

Review / Outcome / Practical Analysis

• Framed as a successful proof of concept built in one day.
• Even with imperfect alignment and notch throat depth, results are considered a good starting point for refinement.
• Emphasizes iterative debugging:
  • CAM settings (e.g., tangent lead-in, overcut)
  • Mechanical fit and fixture alignment (spring clamp, pivot behavior)

Key “Tutorial / Guide” Takeaways

• How to align tube center with nozzle center using scribes/calipers.
• How to model tube notches in CAD using Onshape:
  • Frame + Frame trim + sheet metal conversion
• How to export and CAM program notch profiles in SheetCam:
  • Orientation, lead-in/out settings, overcut, and consumable/electrical choices
• How to iterate on:
  • Toolpath settings (perpendicular vs tangent lead-ins, overcut adjustments)
  • Mechanical constraints (spring clamp, tube load behavior)

Main Speakers / Sources

• Primary speaker: The video author/host (speaks in first person throughout).
• Referenced tools:
  • Onshape (CAD functions like Frame / Frame trim / sheet metal conversion)
  • SheetCam (CAM/programming)