HOW (Concepts)
PREPARE
- Here is a quick checklist to help check to see if your model is printable.
3d Printing is intended for the printing of “parts”, not necessarily an entire model. Think of ways to break down your model for more efficient printing if printing the whole thing is not feasible due to modeling complexity or size. Parts can easily be glued together with cyanoacrylate and sanded for the appearance of a whole object. BUILD _ Build a “clean” model Model with precision to ensure printability. All models must be solid or made up of thickened surfaces. Surfaces and solids should be a minimum of 1/8” thick and all edges should meet precisely. Your models must be “water tight,” similar to a chocolate easter bunny. Make sure to scale your model to the size it will actually be printed. It is best to do this right in your modeling software. Remember that your print size limit is 8”x10”x8” deep.
_ Analyze your model in Rhino This involves checking for manifold edges (edges that intersect), naked edges (exposed edges without thickness), and inverted normal’s (surfaces that are inside out). If you have an extremely complex model, be prepared to spend additional time repairing irregularities listed above or remodeling parts completely. (More on this below in the (HOW) Technical Section.)
_ Analyze your model in MiniMagics 2.0 From Rhino you will export the part(s) as an .stl file. Import the .stl into MiniMagics2.0. This is free software that analyses your part for errors not found in Rhino. Students must run ALL files through a MiniMagics check prior to submitting their job for printing. Fix all errors found in MiniMagics and run again to ensure a clean job. HOW (Technical)
SURFACES Printing layers A 3d printer prints layers (for a Zcorp powder printer, the layers are 0.0034 – 0.004 inches thick) of material and binder. Each layer is defined by the area circumscribed by a closed profile. If any profile is open, intersects itself or another profile, or contains overlapping curves, the model is non-manifold and may not print correctly. Types of non-manifold surfaces: - Naked edges (open surfaces or holes) - Self-intersecting surfaces - Intersecting volumes - Coincident surfaces/edges (overlapping surfaces or edges)
_ How to check whether a model is manifold in Rhino To check whether your model is fit for print, select it and type volume. If the volume is calculable, then it’s good to go. Otherwise, you’ll see the message “Some of the objects are not closed. This calculation is only meaningful if the selected objects fully enclose a volume. Would you like to continue?” If Object is closed this is the window you should see. In addition, if a model is manifold, then all surface normals will point in the same direction. To check the surface normals, make sure all the surfaces are joined (Join) and type Dir. (see more about surface normals below, VOLUMES)
_ Troubleshooting If the volume is not calculable, then the model is non-manifold. To check for: -Naked edges: Select the object and type ShowEdges. Both naked edges and coincident edges will be highlighted. Click Naked Edges to show any part of the model that is not fully closed.
-Self-intersecting surfaces: No way to check- use MiniMagics -Intersecting volumes: Type Check. If more than one polysurface object is listed, you have multiple volumes. Select the model (make sure it’s joined) and type Intersect to identify where the volumes meet. -Coincident edges: Select the object and type ShowEdges. Both naked edges and coincident edges will be highlighted. -Coincident surfaces: Explode the model (Explode) and type Intersect. Then, type SelPolyline. If any polylines are highlighted, there are coincident surfaces.
_ Rebuilding There are many ways to correct a non-manifold model, but the best is to rebuild it using curves (if working in Rhino). In Rhino, curves are defined by type, degree (the amount of curvature), and the number of control points. Curves: In turn, these attributes define the surfaces built from them. Each method for creating a surface has its own properties. If your model requires different surface types, it’s important to keep these in mind. For example: -Lofting Lofting preserves the attributes of the curves used to create the surfaces, but since it uses curves in one direction only, the open edges of the surface may be unpredictable. -Sweeping Sweeping redefines the rail curves as interpolated curves, with control points spaced according to curvature. -Curve Network
A curve network redefines the edge curves as 3^{rd} degree rebuilt curves with evenly spaced control points. Consequently, any corners within a curve will become rounded.
Surfaces: copy written by: Kelly Bair, Assistant professor, College of Architecture, Design, and the Arts, University of Illinois Chicago |
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