Is Your CAD Suitable for Printing and Production?
By Sarah Gold, Associate Product Developer, RIVA Precision Manufacturing
Whether you are a new CAD modeler, an independent designer, or a jewelry contractor, the stage between acquiring a finished CAD and moving forward with the printing process can be very stressful. Is it printable? Is it manufacturable? Is it practical? Is it what the design asked for? Here are some tips for how to inspect your CAD model in Rhinoceros 3D so that you can avoid printing errors, manufacturing issues, and design deviation.
Is it printable?
Rhino is NURBS modeling software, which means that things built in Rhino are actually just shells. These shells will only be interpreted by the printer as solid objects if they are “closed” objects. The fastest way to check if you have a closed object is to select the object (it will turn yellow when selected), then click on the “Properties” tab and read the box next to “Type.” If it says Closed Mesh, Closed Surface, or Closed Polysurface, then you are in good shape. It most likely is printable. If you don’t have a closed object, then you can click on the “Analyze” dropdown menu, hover your mouse over “Edge Tools,” and click the “Show Edges” command. You can checkmark “Naked Edges,” or “Nonmanifold Edges,” to view problem places and click “Zoom” on your pop-up window if you can’t see the problem places highlighted in pink.
Ask your 3D Printing Service what the constraints of their printers are. Details to keep track of include the minimum dimensions for supported wall thickness, unsupported wall thickness, supported wires, unsupported wires, raised detail, sunken detail, escape holes, and clearance. Measure your CAD model to make sure that it accommodates these minimum dimensions. Otherwise, your resin could result in mushed detail or partial build. View the model carefully from all views, particularly in the Perspective view. Change your view to “Shaded” by clicking your mouse scroll, then left clicking the grey sphere, symbolizing Shaded Viewport. In Perspective view, hold your right mouse key to spin. Shift and hold the right key to pan. Ctrl and hold the right key to zoom or use the mouse scroll to zoom. Be on the lookout for any spots that seem small, pointy, or coincidental in proximity. You can click on your “Drafting Tab” to utilize Horizontal, Vertical, and Aligned Dimension tools. Drafting Dimension tools mostly ignore depth of measurement and are good for simple front/side/top dimensions. More tricky angles can be measured using the method detailed below.
Is it manufacturable? Is it practical?
Learning how to accurately measure in Rhino becomes even more essential when assessing the manufacturability of your object. You must learn how to use the “Distance” tool from the “Analyze” dropdown, which is most accurate when used with Snaps. The Snap window can be opened at the bottom of your screen by clicking on “Osnap.” Quad is the most useful and accurate snap to checkmark, but sometimes you will have to checkmark End, Mid, Cen, Near, or Int. To understand how snaps work, you must first understand that NURBS models are made up of a complex series of seams, isocurves and edge curves. Rhino snaps to seams, edges, lines, and points. If you have trouble snapping to a particular spot, it means that it is not reading a seam, edge, line, or point at that location. You can use the tool “Extract Isocurve” to make a curve that can be snapped to or estimate by eye in order to pull a dimension from such a location.
One example of a manufacturing concern is the distance between stones. This can be measured by activating the Distance command, then hovering your mouse over the closest part of one stone, then clicking when a rectangle denoting Quad or End pops up, and finally click the closest part of the second stone. This distance should ideally be 0.2mm. Don’t use Quad AND End to measure; it is safer to use Quad and Quad, or End and End.
Ask your engineer, bench jeweler, and stone setter about other details that you should measure. It’s good to keep a running list of dimensions they require to deliver the highest quality product.
Is it what the design asked for?
You’ve made sure that your CAD model is printable, castable, manufacurable, and wearable by measuring key details. Now, does it stay true to the design? Measure important design details such as stone size, ring size, letter thickness, and/or overall dimension.
Additionally, be aware that most 3D printing services only accept STL files. You can convert to STL by clicking “Save As” and changing the dropdown from .3dm to .STL. Converting your file to STL will convert your NURBS object to mesh. This can do funny things to the design if there is complex stitching involved, so make sure to go to the “Render” view and spin your model around. Change your view to “Render” by clicking your mouse scroll and left clicking the blue sphere, symbolizing Render Preview Viewport. The process of spinning your rendered model will also help you spot design issues in the surface of your model, such as inconsistent surface or unattractive curvature. Other useful tools to assess your surface include EMap, Zebra, Curvature Analysis, and Draft Angle Analysis, all found in the Analyze dropdown menu next to Surface.
As you can see, assessing your Rhino model for printing and production requires learning to move within Rhino, measuring your model, and changing viewports, as well as open communication with your 3D Print service, bench jeweler, and stone setter.