Author Topic: Splitting solids in Meshmixer  (Read 306 times)

TheClumsyOne

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Splitting solids in Meshmixer
« on: August 08, 2017, 09:08:44 PM »
Hi all,

I've got a somewhat complicated part where I want to print inner regions (of irregular shape) in one color and the rest in a different color. I have no trouble selecting the appropriate faces and hitting Y for separate, but then the problem arises that the part I separated is composed of 2 shells since STL files are hollow. Make Solid sometimes works, sometimes doesn't. The same applies for the part I separated from. I tried to make the entire thing a solid and then do the separating, but either Meshmixer doesn't actually produce solids or the select function can only select surfaces since I get the same result this way. I tried using Inspector to close holes, but depending on the geometry this has variable success (for 2 flat surfaces with nothing in the middle it unsurprisingly fails).

I also tried selecting and then using the Create Solid Part feature...but the thing that it creates is the same 2-shell object - in other words, not a solid. What this boils down to is I can't print these parts since printing requires watertight geometries or solids.

So...is there a way in Meshmixer to split off a solid piece from a solid geometry? Keep in mind I'm not talking about Plane Cut - I want to choose a region of my geometry to separate that isn't necessarily a clean split on a plane.

Thanks in advance!

MagWeb

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Re: Splitting solids in Meshmixer
« Reply #1 on: August 09, 2017, 04:38:56 PM »
Not sure about your issue and your printer's technic. But I assume this scenario:

You've a hollow object. This is made of two, not connected shells. You want to get a single object where the outside is printed in a color A(white) and its inside surface in color B (black).

I would do it this way on a dual extrusion printer using Slic3r:

Leave the object as it is but construct a "Modifier object"
in MM SELECT the outer surface and run Edit/Extract with Direction set to Normal and a negative Offset in value smaller (maybe half) than the objects wall's thickness (you may use ANALYSIS/Measure  (local thickness) to check this distance. Details see: http://www.mmmanual.com/measure/). This creates a third shell which is selected now (you can't see it). Hit Y to separate this shell as an object.
Export both objects A( the original) and B (the third shell).

In Slic3r import (Add) object A. This active go to Settings (gear icon). Now "Settings for A" dialog will pop up. Click on LoadModifier and import B as an modifier object. Activate B in the upper treeview list and set the second extruder (assuming the inside color, black, filament is feeding to this) while you leave A at the default (first) extuder (outside color white feeded to this). Confirming this dialog Slic3r should create GCode where the intersection of A and B ( means inside of A and B) is printed with black (using extruder 2) while the difference A-B (outside of B) is printed in white (extruder 1).
« Last Edit: August 09, 2017, 04:41:51 PM by MagWeb »
I'm just a user as you are. Being no Autodesk employee: I do not know where this road will lead to, nor do I claim to've all stuff got right.

TheClumsyOne

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Re: Splitting solids in Meshmixer
« Reply #2 on: August 09, 2017, 05:25:33 PM »
Thanks for the advice - let me explain more clearly. This is an image of the part I'm trying to print:

segmenting.png

The lighter region I want to make a separate object so that I can print it using gold filament. The rest will be red. So when I use Select and Separate, I get

segmented.png

Since this is an STL and is hollow, separating that region gives me a non-watertight shell. I tried Make Solid and

solidfail.png

It has trouble generating the solid for some reason. If I change the settings (such as Mesh Density) the result doesn't change. I have also tried selecting the boundary of the opening and using Erase/Fill, but that doesn't work either. I tried Remeshing the entire part to increase the number of elements, but that had no effect. I tried using Bridge but that function aborts everytime I use it without fail.

MagWeb

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Re: Splitting solids in Meshmixer
« Reply #3 on: August 09, 2017, 05:44:23 PM »
Ah, I see....

Using Bridge you're on the right track.

Bridge needs exactly two selections at the open boundary. Both selection have to be not interrupted by not selected faces at the boundary.
Do Bridge at the flattened tip edges and maybe at one side of that upper inner corner. Fill the remaining holes at the "sides" using Inspector.
I'm just a user as you are. Being no Autodesk employee: I do not know where this road will lead to, nor do I claim to've all stuff got right.

TheClumsyOne

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Re: Splitting solids in Meshmixer
« Reply #4 on: August 09, 2017, 06:47:18 PM »
That worked immensely well! Thank you for explaining the Bridge function...I was wondering why it always failed.