wardjr wrote:

Just to clarify for the community, could you explain the main advantages of making a hallow model .vs simply using a solid model and setting infill to zero?  (Setting 4 bottom layers, 4 top layers and say 3 perimeters with zero infill)
Excellent tutorial Pirvan!!!

There probably isn't much of a difference.  The only thing you'd need to worry about it the top wall/roof overhangs, since there's nothing to support them.

Frankly it's just an exercise in modelling.  Sometimes you might be able to apply the technique to thicken a surface that's just to thin to print or structurally too weak.  You could also make an argument that it gives you more control of the wall thickness and accuracy.

Actually, this is an important skill to have if you plan on sending your parts for SLS printing at sites like Shapeways. Those machines don't have an "infill" setting, so by default your model is printed 100% solid, which is very expensive. Shapeways always told us to hollow the model and place a small hole for the powder to fall out. It saves a lot of money, but doesn't necessarily make a weak part if your wall thickness is at or above their recommended thickness.

n2ri wrote:

well I done it to a model and left bottom out also making like a real shell with only sides and top at thickness chosen on a 2 part model of like a submarine so it could be printed in clear ABS and paint non-glass window areas and put interior details in then assembled. Acetone vapor will likely need done to smooth clear enough to see through or at least use some "Testors clear cement" like they sell for such things on plastic models. while making hollow there are other tools in Meshmixer that allow manipulation of surfaces for this where you can remove parts of shell.

I gave Meshmixer a try and it can do basically the same thing much faster and simpler.

If you want to give Mesh Mixer a try, load up the object, then use CTRL-A to select it, then click Edit/Offset, and in the dialog box select a Distance value (in this case -2mm), then click Accept.  That's all there's to it.  It will create an inner shell 2mm offset from the original.  Export the STL and you're done.

yes thats what I used.

well I done it to a model and left bottom out also making like a real shell with only sides and top at thickness chosen on a 2 part model of like a submarine so it could be printed in clear ABS and paint non-glass window areas and put interior details in then assembled. Acetone vapor will likely need done to smooth clear enough to see through or at least use some "Testors clear cement" like they sell for such things on plastic models. while making hollow there are other tools in Meshmixer that allow manipulation of surfaces for this where you can remove parts of shell.

I gave Meshmixer a try and it can do basically the same thing much faster and simpler.

If you want to give Mesh Mixer a try, load up the object, then use CTRL-A to select it, then click Edit/Offset, and in the dialog box select a Distance value (in this case -2mm), then click Accept.  That's all there's to it.  It will create an inner shell 2mm offset from the original.  Export the STL and you're done.

wardjr wrote:

Just to clarify for the community, could you explain the main advantages of making a hallow model .vs simply using a solid model and setting infill to zero?  (Setting 4 bottom layers, 4 top layers and say 3 perimeters with zero infill)
Excellent tutorial Pirvan!!!

There probably isn't much of a difference.  The only thing you'd need to worry about it the top wall/roof overhangs, since there's nothing to support them.

Frankly it's just an exercise in modelling.  Sometimes you might be able to apply the technique to thicken a surface that's just to thin to print or structurally too weak.  You could also make an argument that it gives you more control of the wall thickness and accuracy.

yes some STL models have walls too thin and Slic3r cant thicken them. Meshmixer can and you control exactly how much and even what side to leave as designed (outside or inside). I am planning to use that on some N scale locomotive shells to strengthen them without shrinking inside too much to slide over chassis/motor

Just to clarify for the community, could you explain the main advantages of making a hallow model .vs simply using a solid model and setting infill to zero?  (Setting 4 bottom layers, 4 top layers and say 3 perimeters with zero infill)
Excellent tutorial Pirvan!!!

There probably isn't much of a difference.  The only thing you'd need to worry about it the top wall/roof overhangs, since there's nothing to support them.

Frankly it's just an exercise in modelling.  Sometimes you might be able to apply the technique to thicken a surface that's just to thin to print or structurally too weak.  You could also make an argument that it gives you more control of the wall thickness and accuracy.

Step 6.  Now that the inner mesh is selected, we need to invert it.  To do this, select Filters, Normals, Curvature and Orientation, then Invert Faces Orientation.  In the filter dialog Window, click Force Flip and Flip only Selected Faces, then click Apply

Step 7. Deselect the mesh:  Filters, Selection, Select None.  In the Dialog, click both boxes, then Apply.  You'll notice the mesh will be completely black.  That is because you're looking at the back face of it now.

Step 8.  In the Layers window, click the eye next to the original mesh to make it visible once more.  We will now join the two meshes into a single mesh.  Right click on any of the 2 meshes in the Layers Windows, then select Flatten Visible Layers.  In the dialog box, check Merge Only Visible Layers, Merge Duplicate Vertices, and, optionally, Delete layers.  This last one will delete the original layers and leave you only with the newly merged mesh.  If you want to keep the original layers for further tweaking, don't check this box.  Click Apply.

And that's it !  You now have a hollow model.  Save the new mesh to a STL.  If you want to check out the result and see how it came out, you can open it in NetFabb, then use the cut feature to create a section view.

Happy modelling !

If you want to do this yourself, it can be (relatively) easily accomplished using Meshlab.  This tutorial will explain how it's done.

Step 1.  Open your model in NetFabb, and check for errors.  Fix the errors (automatic fix usually works).  Next open up your model in MeshLab.  Click the Show Layers Dialog icon to open up the layers window.

Step 2.  From the Filters menu, select Remeshing, Simplification & Reconstruction, and Uniform Mesh Resampling.  On the pop-up dialog box, make the following changes: ON the Precision % dialog box, enter a value less than 1%.  The lower the number the more precises the reconstruction, but the longer it takes, and the number of polygons increases dramatically.  For the offset, we'll use an absolute number.  IN this case, the vaue is 2 (as in 2mm.  A positive number will create a shell on the ouside of the model, a negative number on the inside, so we want a negative number.  Last but not least, check the Cean vertices and Multisample.  This increases accuracy, and cleans up the resulting mesh.  Click apply and wait.

Step 3.  Once the filter has finished its job, you will see that a new payer has been added:  Offset mesh.  You can't see it because it's inside the original mesh, so click the eye of the original mesh to hide it and see the newly generated offset mesh.

Step 4. The new mesh's faces/polygons, are currently facing the same way as the original mesh, but it needs to be reversed, if it 's to become the opposite side of the shell/skin.  So first make sure you select the correct layer to work on from the Layers window (Offset Mesh), then from the Filters menu, select: Selection, then Select All.   This will select everything on this layer.

Step 5.  You may also notice some stray bits and pieces, that may have been generated during the reconstruction process.  If you do see those (as you can see in the image below, you should clean those up by selecting and deleting them.  Once the model is clean, apply the filter described above to select the mesh, and click Apply.

Continued on the next post.