KDE Logo with draft

For die cast, the positive model should have a draft. That is, its sides should not be exactly vertical, but taper towards the top.

FreeCAD offers an extrude function to apply a thickness to a 2D design. This extrude function has a Taper Angle parameter to achieve exactly that.

Unfortunately the taper angle parameter only works for polygons up to a certain complexity.

Here is an alternative approach that works with shapes of any complexity:

• Given a shape in the X-Y plane
• Don't extrude along the normal (or Z-Axis), extrude along a user defined axis that is somewhat off to one side. E.g. (0.1, 0, 1) extrudes mainly along the Z axis, but shears the object slightly into X-Direction.
• Extrude the shape multiple times, using all possible combinations of -0.1 or 0 or 0.1 in each of X and Y dimensions. That is 8 combinations.
• Apply a union operator on the 8 extrusions.

The resulting objects is (roughly) tapered.

The KDE logo has sharp inward pointing corners in the center of the letter K. This produces artefacts of multiple sharp corners with gaps in between. Instead of only three values -0.1, 0, 0.1 one could use a finer subdivision sequence like -0.1, -0.08, -0.06, -0.04, -0.02, 0, 0.02, 0.04, 0.06, 0.08, 0.1 to prevent this. The union operator may take very long then.

To not enter a tedious manual process and much waiting, I've simply used blender to post-process the STL mesh to even out the artefacts where visible. It was only a few.

The taper is quite strong in this model. Some of the gaps close. You may ease that, by cutting a thinner slice out of the STL, e.g. with cura or slic3r, and then scale the Z-dimension up.

Category: 3D Printing