What should the design consideration be for the radius of fillets in FDM?

In Fused Deposition Modelling (FDM), the radius of fillets is an important design consideration that impacts both the mechanical properties of the printed part and the success of the printing process. Choosing a fillet radius that equals the inner radius plus the wall thickness ensures that there is sufficient material in the transition area. This creates a smoother transition between surfaces, which can help reduce stress concentrations and improve the overall strength of the component.

By maintaining the fillet radius in relation to the wall thickness, the design helps to prevent weaknesses that might occur if the fillet is too small. A larger radius can also aid in enhancing the layer adhesion during printing, as it gives the molten filament more surface area to bond during deposition. This combination of mechanical integrity and printability makes this design consideration critical in the successful application of FDM.

Choosing the fillet radius based on arbitrary choices or unrelated factors, such as material cost or the relationship between outer and inner radii, would not provide the same structural benefits and could lead to issues with the printing process or the part's performance.