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Digital Detaling

Applying texture to CAD models for 3-D printing

By Darla Alvarez

Most bench jewelers would agree that applying texture to a piece is best done post-process once the piece is cast, but sometimes that is neither practical nor desired. In part one of this article series, we will look at how to apply a texture in Rhinoceros 3D. In part two, we will look at how to apply a texture in ZBrush.

Many are undoubtedly familiar with applying texture for render purposes, usually by extracting a surface. The geometry applied, however, is not actual 3-D-printable geometry—and extracting surfaces creates open objects that cannot be 3-D printed. The following demonstrates how to apply 3-D printable texture in Rhino with displacement settings, using a half-domed band as an example piece.


Digital Texture 1

1. Start by creating a half-domed band of the desired dimensions using Sweep1. For this example, the band is size 7, measuring 6 mm wide and 2 mm in depth. This becomes a template for the textured band.


Digital Texture 2

2. Alter the cross-section curve so it goes into the opening for the finger by turning on control points and moving them inward with Gumball. Do not bring it to or across the origin as this will result in either a singularity or self-intersecting surface that will prevent a later Boolean function from succeeding. The sweep will update with history.


Digital Texture 3

3. Under the Render menu, select “Effects,” then “Displacement.” Select the ring as the object to apply displacement to and press enter. Next, click on “Click to Assign Texture,” then “Create New Texture,” and then “Import from Texture Library.” Rhino includes a number of default textures, or you can import a different texture from elsewhere.


Digital Texture 4 Main

4. Any image can be used, but for best results, use a grayscale image. This example will use the Rhino Hammered texture. Once the texture is selected, click on the pencil icon where the current texture shows to open a secondary Editing dialog box, which can be broken down as follows:

Digital Texture 4 A

a. Current texture.

Digital Texture 4 B,C,&D

b. UV Offset. This is used to adjust the image offset, akin to shifting the image horizontally and vertically. For the example, it is set to 0.
c. Repeat. This sets the number of times the image will be tiled horizontally and vertically. For the example, it is set to 5 in U and 5 in V.
d. Rotation. This changes the angle of the image. For the example, it is set to 0.


Digital Texture 5 Main

5. Once set, press OK to return to the “Displacement Settings” dialog box, which consists of the following:

Digital Texture 5 Detail

a. Current texture. Click Edit to reopen the Editing dialog box. Note there is a Preview option at the bottom so changes can be made and then viewed prior to accepting.
b. Displacement. Black Point sets the elevation of the color black in the image. White Point sets the elevation of the color white in the image. For the example, Black Point is set to 0.4 and White Point is set to 0, thereby pulling the black portion of the image above the white.
c. Initial Quality. In general, setting this to Very High will produce a texture with a high enough resolution to be usable. Very High, however, uses more memory, which means the Mesh Memory Limit may need to be increased, depending on the texture.
d. Fairing. This will smooth out rough edges. A higher number sets how many times fairing will be applied. It is not necessary to use Fairing for this example.
e. Mesh Memory Limit. This controls how much memory is allocated by the displacement mesh. In order to get a high resolution mesh, this number may need to be increased. For the example, it is set to 512. Click OK to accept the settings.

While other settings exist in both dialog boxes, these are the primary settings used when creating a texture on a model. These settings can always be revisited by selecting the object, going to the “Properties” tab and clicking on the “Displacement” icon.

At this point, the applied displacement is just a render preview. Click on the band to reveal the actual shape of the model. To apply the displacement, type ExtractRenderMesh in the command line. (This command does not exist in the toolbars or in the menus, so it must be typed.) The render geometry becomes actual geometry as a mesh object and can be 3-D printed.


Digital Texture 6

6. Select the mesh and hide it. You will see that the polysurface version of the model still exists. The texture can be turned off by accessing the “Displacement Settings” under the “Properties” tab and unchecking “On” in the “Displacement Settings” dialog box. Put the polysurface on a different layer and turn the layer off. Show the displacement mesh. If the texture is meant to be all over the object, then the application is complete.


Digital Texture 7

7. In the case of the band example, some of the texture needs to be cut away. Scale1D the band slightly wider so the side texture can be cut away to reveal straight sides. Create a box on each side of the band that is larger than the band. Be sure to place them so the band will be 6 mm wide once cut.


Digital Texture 8

8. As the band is a mesh, NURBS Boolean commands cannot be used. Instead, go to the Mesh menu, click on “Mesh Boolean” and select “Difference.” Perform a Mesh Boolean Difference command using the polysurface cutters.


Digital Texture 9

9. Select the rail used for the sweep and extrude the circle to form a center cutter. Perform another Mesh Boolean Difference to clear out the center of the band. The band is ready to prepare for 3-D printing.


Digital Texture 10

10. Applying texture within CAD can be the answer from time to time and is a great way to expand the CAD user’s repertoire.


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