Customizable offset pipe reducer

thingiverse

I thought I would need to make an eccentric pipe reducer recently for a new cooker hood ductwork. OpenSCAD's cylinder command doesn't allow the axis to be skewed so I didn't model it. Fortunately we were able to fit the ducting without it. This model allows the user to specify two pipe inner diameters and wall thicknesses. The upper pipe can be offset by a percentage of the radius (0% is concentric, 100% is fully eccentric) and the centre can be rotated if required (though both axes run vertically). Finally, the gap between the two pipes can be specified and whether the inner wall or outer wall should take precedence for modelling. With 100% offset and a narrower upper wall, the pipe will run through if the inner wall takes precedence. There would be a step in the outer wall. If the outer wall takes precedence, the opposite would be true. (Its easier to see than describe - have a play!). Print Settings Notes: I haven't tried printing this model, just run it as a modelling exercise. I check sliced several STL outputs with Repetier to see if the solids were manifold. How I Designed This I've now revisited the project as a modelling exercise. The transition piece has been modelled as a set of polyhedral blocks in order to ensure that varying wall thicknesses (specified by upper and lower parameters and implied by the rotational geometry) all calculate correctly. Trying to reduce the number of faces to just inner and outer surfaces causes non-manifold problems so I've left the full polyhedron definition in place.