Using SCAD primitives to create fillets
thingiverse
The primitives provided by the SCAD language, in particular the minkowski() operation, can be used to automatically add fillets to every concave seam of a piece. However, the operation is expensive and probably not a feasible way to approach things. This scad file shows a shape made of three interlocking cuboids and a cylinder filleted using a very polygonal sphere. A finer-resolution sphere would produce a far better result, but on my middle-aged macbokk would take hours or more to compute.
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