DM Lab TutorialWritten by John Eberhart

3D Printing Prep using Rhino and Geomagic

When you are ready to prepare your model for 3D Printing, you have to properly prepare the model so it can beprinted.

1. The 3D printer cannot print 2Dsurfaces, they always have to be3D objects. (Made out of joined2D surfaces)

If you have a 2D surface you need toprint, use the offset surfacecommend in Rhino to offset thesurface and make it a 3D volume.

Note: Use the “solid” offset surfaceoption in the command prompt.

Single Surface(Will not 3D print)

Same Surface offset into asolid volume.(Will 3D Print)

2. All 3D volumes have to be completelyclosed, no holes or gaps between thesurfaces.

When the 3D printer Software processes a 3Dmodel for printing, it projects a series of crosssection curves through the model, each crosssection curve needs to be a closed curve, thatway the software knows what to fill and whatnot to fill.

If the object to be printed has a hole or a gap inthe surface, it will create an open curve.

Part with a gap in the surface,creating an open curve.

Part will not 3D print

Part without a gap in thesurface, creating a closedcurve.

Part will 3D print

Gap in Curve

3. You cannot have self intersecting surfaces or volumes, model has to be a SINGLE 3D volume.

3D Part to be printed. 3D Printer createscross-section curvesfor each print layer.

Any cross-sectioncurves with a gapmeans the fill areacannot be calculatedand the part will fail.

If all cross-sectioncurves are closed, 3Dprinter can figure out fillpatterns and the partwill print.

GAP!

You have to create models that are made of one surface, you cannot have two volumes intersect each other. Whenyou generate a STL model for the printer, a mesh will be created around each volume and not around the entire part,this causes issues with the 3D printer when it tries to print the 3D part. The easiest way to fix this is to use theUnion tool to merge all closed polysurfaces into one. (Solid Menu>Union) If this does not work, you will have tomanually reconstruct your objects so you do not have surface intersections.

Object withintersectingsurfaces-Not Goodfor 3D printing

Object with nointersectingsurfaces-Good to3D print.

Step One: Make sure your model is scaled to the size of the3D print you want to make

Step Two: Move the model close to the Rhino Model Origin,and place the model in the positive X,Y, and Z quadrant.

Step Three: Select all the surfaces to be exported and jointhem into a single poly surface.

Preparing your models in Rhino for export asStereolithography files:

If you have a polysurface model, a model made up of manysurfaces, you need to do the following things in rhino.

To show how the surfaces should be trimmed, I pulledthe two volumes away from each other and you can seethat each surface was notched to receive the other andthere are no surface intersections or internal surfaces tothe model.

If your model has any intersecting surfaces, crossingsurfaces, or internal surfaces, the 3D print will fail.

Step Four: Deselect the model and tryreselecting it. If the entire model does notreselect, then you have gaps in your modeland you need to work on your model so all theparts of your model will join together

Joined Surfaces

Non-Joined Surfaces - PROBLEM AREA

In this case, the feet are extruded cylinderswhich are already polysurfaces and cannot bejoined.

To fix this model, explode the polysurface anddelete the cylinder surface that is between thecylinder and the rest of the part.

Repeat Step 3 and see if the parts all jointogether.

All parts are now joined into one poly surfacemodel.

Note: If you cannot get your part to join, youwill need to remake this part in rhino, takingextra care that the model is well built.

Step Five: Once your part is joined, select thejoined part and choose:

Mesh>From Nurbs Object

The following window will appear.

Adjust the slider and hit the preview button.

This will preview a new mesh model that wewill export as an STL file.

Note: For a square shaped or a model withmostly flat faces, you can use a lower polygoncount.

Models that are curvy, you should use a higherpolygon count.

Caution:Higher polygon count = Larger file size andmore time to process down the road

Click OK to create the new mesh file

The two models will now be on top of eachother. To select the mesh model, choose:

Edit>Select Objects>Polygon Mesh

Selected Mesh Object

Step Six:

Choose: File>Export Selected to save yourmodel as an STL file.

Under Save as Type, choose: Stereolithography (*.stl) and Choose Save

Under File Type, Choose Binary

Make sure that Export open objects is checked.

Click OK to save

For Advanced Users:

If you uncheck export open objects and save themodel AND the following error does NOT appear, youare good to go for 3D printing.

If you see this error, Rhino will only save the portionsof your model that is fully closed.

You will need to go back and check the Export openObjects and proceed with the rest of this tutorial.

Exporting A single surface model for 3D printing:

In Rhino you can convert a single surface into a closedvolume.

To do this, select your surface and choose:

Surface>Offset Surface

With the command active, inthe prompt window, click onthe Solid option, and ifneeded, you can flip thedirection of the offset byclicking on FlipAll.

At the end of the prompt, typein the thickness you want tooffset your surface. In thiscase, .25” (1/4”)

The part will offset and create a closed model.

At this point, follow the procedures on pages 3 and 4 forexporting the model as an STL file.

However, if your modellooks like this:

Using the offset surface inRhino will not work as theoutside and inside of themodel overlaps onto itselfand the part will fail whentrying to print.

If you have this condition,only export the singlesurface as an STL filefollowing the steps outlinedon pages 3 and 4 of thistutorial.

We can do a more sophisticated offset using GeomagicStudio, covered on page 15 of this tutorial.

Opening Geomagic Studio and Checking your Model For Printing:

To launch Geomagic Studio, under the start icon in Windows, choose:3D Apps>Geomagic StudioGeomagic will open with its welcome screen.

Click Open toload your STLfile.

Browse to your file and Choose Open

IMPORTANT: At the pop up window below,choose the same units you were using inRhino. If you get this wrong, your modelwill import either very large or very small.

The following window will then appear.

Choose YES to have geomagic analyze your part andshow you where your problem areas are.

Mesh Doctor willhighlight any issueareas in your modelin red, green, andyellow.

Note: Blue is normal.

Red Areas are surface overlaps, surface spikes, and otheranomalies

Green Edges are gaps between surfaces or surfaces withnaked edges or a surface with a hole.Often when you convert a 3D nurbs model to a polygonmodel the edges of the surfaces do not align when theyexport. This can create very small holes when the model issaved.

Yellow Areas are the back side of a surface - Note: if youhave Yellow polygons mixed in with Blue polygons, then youhave backward facing surfaces. If that is the case, you needto go back to Rhino and fix the model.

See page 11 for instruction on that.

Note: Iintentionallymade a hole here

Within Mesh Doctor, there are a number of tools we can use totry and remove some of these errors.

First Try: Run Auto Repair, this will try to remove as manysimple issues as possible.

Click the Auto Repair icon and then Click Apply

After running the Auto Repair, check your model.Mesh Doctor repaired the model but there are still issues.

This can deform your model, if it does, hit cancel and proceedto the next steps.

In this example, mesh doctor fixed some issues but I still have problems. This model is still not ready for printing.

Warning: Mesh Doctor in trying to fix the model, may actually make it worse. If that is the case, undo the meshdoctors changes by hitting Control-Z, and process to the manual steps listed in the next pages.

If after running mesh doctor and your model does not have any holes, there is one final step you need to performbefore saving your model for 3D printing, which is make manifold. If your model looks good after running the meshdoctor, skip to page 13 and run the make manifold command.

Hole in model

New Hole Appeared

Gaps in surface stillremain

Filling Holes and Thickening Parts: Mesh doctor will fix most minor issues. However, if youhave large holes in your model, you have to fix themindividually.

Under the Polygons Tab, choose the Fill Single icon.

Note: By clicking on these arrows, you can scroll througheach hole and repair it.

With the tool active, mouse over anopen hole and it will highlight red. Ifyou click it, it will fill the hole.

Click back on the fill hole icon to endthe command and apply thechanges.

Highlighted Hole edge

Filled Hole

Model with filled holes.

At this point Try Running theMake Manifold Command outlinedon Page 13 of this tutorial.If it works you are ready to 3Dprint.

If that did not work, the next thingyou can try is the thickencommand.

Backwards Facing Polygons:Sometimes you will get a numberof triangles that are backwardsfacing (Yellow) or have wild spikesto them. You can select anddelete these faces on the model,and then use the fill holes tool torepair the hole.

The Thicken Command:

Often when you convert a 3D nurbs model to a polygon model theedges of the surfaces do not align when they export. This can createvery small holes when the model is saved.

The easiest way to fix this is to thicken the polygon mesh veryslightly so that the model expands, a new mesh is created and thepart will be closed.

Under the polygons tab, choose Shell>Thicken

Your model will turn Red and the thicken options will appear.

Under Thickness, set thisto a very small amount. Inthis case .001 inches.

Click Apply to see thechange. You can adjustthe thickness. Once it isgood, click OK.

The final step is to run the Make Manifold Command to perform before saving your model for 3D printing, skip topage 13 and run the make manifold command.

Run Make Closed Manifold to verify your File will Print:

Run the Make Closed Manifold command to verify you have no issues with your 3D print. If you perform this test,and some or all of your model disappears, you still have issues. If the model blinks but is still there after performingMake Closed Manifold, you are good to go.

Click on the Polygons Tab

Click on the Manifold Icondown arrow, and choose:Make Manifold (Closed)

My model disappeared when I ranthis command. So this model stillhas problems.

Hit Control Z to undo and yourmodel will reappear

If your model disappears while running the Make Closed Manifold command, you have to go back and try to identifythe problems. If you cannot figure out what the issue is, see a DM staff person.

Saving your Closed Manifold Model for 3D printing:

WARNING: You have to successfully run the make Closed Manifold command BEFORE saving your part. Forinstruction on how to do this, see page 13 of this tutorial.

Click on the Geomagic icon in the application ribbon.Choose Save as.

In the save as window, browse to the 3D printer drop box:

\\archserver1\class folders\3D printer drop Box\your name\your file.stl

Make a folder with your name on itand choose that folder.

Under File of type, chooseSTL (Binary) File (*.stl)

Click Save to save your file.

You are now ready to print your model. See a DM staff person and they can now print your file.

Offsetting a 2D Surface into a Uniform 3D solid:

Geomagic can offset and make solid very complex 2Dsurfaces that are suitable for 3D printing.

Import your Surface model from Rhino and open it inGeomagic. (See Page 7)

Under the Polygon Tab, Choose:Shell>Shell

Under Thickness, import a desiredthickness.

Note: If you want to reverse thedirection the model will thicken,input a negative value.

Hit Apply to preview the thickenedpart.

You can adjust the thicken valueand hit apply again to change, or ifyou like the thickness, choose: OKand the 3D part will be created.

Thickened Part

Follow the steps on page 13 and 14 to verify the part isready to print and save your part to the printer drop box.