Steel is critical because you are cutting with heat, and heat will translate into deflection over time of heating and cooling. Aluminum has a much lower melting point which results in higher risk of deflection in your CNC system when you are cutting from the heating and cooling. The steel construction brings a higher rigidity allowing you to add thicker plate without risk of sagging or bending in the frame. The steel gantry is critical because the heat of your cutting will rise and this will affect the cutting tolerances if you accept a machine designed with cheaper materials like extrusion. This is why on larger higher priced machines you only see steel. Just because you are spending less does not mean you want to get a less rigid design. Our FEA software shows the strengths of our machines and minimizes the deflection which maximizes your cutting tolerances.