Author Topic: How to cut a hollow object in half but have closed off ends?  (Read 120 times)

TronLives

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How to cut a hollow object in half but have closed off ends?
« on: January 03, 2018, 01:53:46 AM »


I'm very new to this.

I have a hollow object that looks solid from the outside. For example, a hollow cylinder. I want to cut this cylinder in half but I want each half to have closed off ends, so they look like two half-sized solid cylinders instead of two buckets.

How would I do this? Is there a way to fill the inside of the cylinder before cutting? Or a way to close off the ends of the two halves after cutting?

The 3D object I'm using is a vehicle (TRON light cycle - ENCOM 786) that has a very detailed inside but looks solid from the outside. I'm going to be using this for pepakura which prints the outside of an object. I need to have the ends closed off after cutting so pepakura doesn't wrap into the inside. Below is an example of what it looks like when it is cut in half.




Thank you

MagWeb

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Re: How to cut a hollow object in half but have closed off ends?
« Reply #1 on: January 03, 2018, 05:08:56 AM »
@ your cylinder example:
Meshobjects do not know the term "solid". There are just surfaces which may be "watertight" or owning some oben boundary.
A hollow object simply combines two surfaces where the outer one's normals point to the outside and the inner one to the inside.
So if there's no error in the mesh (e.g. some connection between inner and outer shell you can split you object into two separated objects (EDIT/SeparateShells).
In your case you want to keep just the outer shell so you may discard the inner one.
Cutting the outer shell will give you wat you want.
(If you want to make the halves hollow you'd need to run EDIT/MakeHollow now)

@ your vehicle model:
You need to repair your model's mesh error before doing anything else.
As a first step you need to get consistent surface normals orientations. The pink areas mean that these surfaces are flipped. Like twisted gloves their "outside" show their "inside". You need to SELECT these flipped surfaces manually and use SELECT/Edit/FlipNormals to get grey surfaces all over.
After this step there are two alternatives:
1st: As a second step I'd try EDIT/CloseCracks to close as much of the open boundaries (the blue lines).
There may still be several boundaries after doing this. Run ANALYSIS/Inspector to fix the errors. Red marked regions will need some modification (maybe deformations) of the existing mesh.
If your model still exists of several surfaces (most likely): Split them via EDIT/SeparateShells and weld them pair by pair via BooleanUnion.
2nd: Run EDID/MakeSolid. You may think of this tool as some global boolean union. Against the upper workflow this tool rasterizes your model. Therefore its result will be nicer the higher SolidAccuracy and MeshDensity are set to (at cost of computation time).
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.

MagWeb

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Re: How to cut a hollow object in half but have closed off ends?
« Reply #2 on: January 03, 2018, 05:27:31 AM »
Just a further note on your source model:
Seems you imported some not indexed file format (e.g. STL)?
These not indexed formats may write several vertices with the very same coordinates. If there are more than two of these redundant vertices MM can't decide which vertices have to be melted to one. This results in several open seams.
If you have access to the app where this model was constructed and its native format version:
Export it as a OBJ instead of STL. On OBJ each vertex gets an index and avoids "not needed" redundant vertices. So your import in MM should be much better.
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.

MagWeb

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Re: How to cut a hollow object in half but have closed off ends?
« Reply #3 on: January 03, 2018, 05:54:44 AM »
In case you have just the STL:

Try another STL-merging technique (on MM's menu: Preferences/File - tab): "RegionGrowing" might help... hopefully
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.

TronLives

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Re: How to cut a hollow object in half but have closed off ends?
« Reply #4 on: January 04, 2018, 01:48:01 AM »
Thanks for the tips MagWeb, very appreciated.