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HOW TO

HOW (Concepts)

 

PREPARE

_              Prepare for an efficient 3d print job

3d Printing is expensive. In an effort to save your resources as well as UIC’s materials, think ahead about how you will construct the model to utilize the least amount of material necessary. This includes modeling in “release holes” for removing excess power that might get trapped in between surfaces.

 

_              Prepare to assemble the model

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.

 

_              Prepare for the physical attributes of a 3d print job

3d Printing can be heavy and, unlike the digital world in which you are modeling, gravity could destroy your printed model. Think about parts that are top heavy (that might not stand on their own once physically printed) and structural elements that are not robust enough (and may need to be exaggerated).

 

_              Discuss any foreseeable printing issues a lab tech

Lab tech’s are pros at identifying potential problems with a 3d print prior to going through the time and cost of actually printing it. If you are unsure of the feasibility, contact a tech to discuss work-arounds with them.

 

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. 


  • Keep Naked Edges highlighted (pink)
  • Type DupEdge 
  • Click on highlighted edges
  • Type Patch 
  • Make sure surfaces are not intersecting 
  • Click on all surfaces and type Join 

-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 3rd degree rebuilt curves with evenly spaced control points.  Consequently, any corners within a curve will become rounded.


            Surfaces:



Example:



copy written by: Kelly Bair, Assistant professor, College of Architecture, Design, and the Arts, University of Illinois Chicago 

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