View Full Version : How do you make a 3D PRINT model (stl) hollow in LW? Any tips?

07-07-2014, 07:52 AM
Hey guys,
I have been doing some work in 3d Printing in LW (using Shapeways) and so far it has been a blast.
I do have a question, Any tips on making an STL file hollow in Lw.

Any suggestions would be welcomed.


07-07-2014, 09:34 AM
Use thicken to give your polygons some thinkness. Not sure what kind of 3D printer tech you are using, but ours would want to build a honeycomb bridge area to fill that void while printing and then it get rinsed away in a ultrasonic cleaner. So if I had a hollow ball printed, that bridge material would stay inside unless we made a way for it escape during the cleansing process. Your printer technology could be different.

07-07-2014, 09:43 AM
This is a little tricky. It's possible to do it this way:

Place a copy of the original mesh, flip the polys, highlight them all, hit Extend, then use Point Normal Move to move at least the minimum thickness distance. At that point, you can again paste the original mesh in and weld it to the new polys.

There's a problem with this. If you're extending those new polys inward, then you'll have some geometry crossing itself. This will probably be impossible to print. If you use Point Normal Move to move outwards, then your new model will not be as precise as the original... the process will soften the look of the model.

I haven't used the Thicken command enough to know if those problems are automatically solved.

I've been using Shapeways, and I discovered that 3D Coat is an excellent tool for some models, for just those reasons. Intersecting geometry and non "manifold" geometry gets automatically fixed via passing through the voxel mode. There's also an option of importing a mesh as a "skin," which lets you specify the thickness.

07-07-2014, 09:50 AM
A couple of 'simple' things you could try:

1. Thicken. This will create an inner shell. It may not be ideal for complicated models though--you might encounter issues in tight areas, especially if you want thicker walls--but give it a shot. If anything, it might work for most of the geometry and, if you're lucky, you'll only need to delete and patch a few spots. If your object has more than one piece, use the the tool on each piece separately.

If the result is not quite what you want, you could try other tools like Extender Plus or Smooth Shift--I don't know if the results will be any different but in some situations the other offset tools might work better. Worth experimenting with anyway.

2. If you're not concerned about closely following the topology of the outer shell, just put some spheres or other primitives inside. If you use spheres, use tessellation mode. Merge together the objects that share space using the boolean tool (3rd Powers Boolean Tool is excellent for this.) Don't forget to invert the new object so the polygons face inward to create the void inside.

Naturally, you'll want to validate the new mesh for 3D printing using the native Mesh Repair tool or a third party program like MeshLab (http://meshlab.sourceforge.net/).


07-07-2014, 02:32 PM
Don't know which Shapeways process you're using. Their capabilities and requirements differ, depending upon which machine they use. I'm not fully up on the natty ins and outs of Shapeways, as we went the in-house route and bought our own medium format printer; far less expensive and I can print at 03:00 if I need to. But, to the "hollow" topic, the slicers we use create hollow prints from solid models. They can be completely hollow, filled with varying percentages of Sparse Infill, in order to either keep the mass down or save materials, or solid. It's all controlled in the slicer. You can set wall thickness of the sides separate from the top/bottom if necessary. You can print a vase from a solid model. The only time I model wall thickness is when creating, for instance, a dome shape, IOW, a cap for a vessel of some sort. This is done printing using only Loops. With 4-5 Loops and proper cooling, you can extend out over an angle of 80+ from vertical without having to print support.

If you really need to model the walls, Thicken is the best way to go. Depending upon the shape, there may be some clean-up necessary to remove overlapping geometry, but it's less prone to create it than the other methods. Usually, you don't want to go that thick but, again, it all depends upon how the model is constructed and its shape. You want high density polys, so that they don't show up in the print. This will create overlaps at tight corners. Just have to deal with it on a case by case basis.

Another way to go is to model the part, use Thicken to thicken outward and then scale the part down to the originally modeled dimensions. This will eliminate the internal overlapping.

07-07-2014, 09:14 PM