I can't hollow out a skull!!! Who can???

[Roxy]

I'm trying to hollow out a solid .STL file of a skull. What I'm hoping to do is make it into a little container where the very top comes off and there is a small container in the open area where the brain would be. l can make it work just fine with OpenScad except it won't render. I can see what I'm doing is OK, but OpenScad can't complete the job. Check this out:

Skull_Coin_Box.jpg

I'm trying to use the attached Skull.STL file as a starting point. (And of course, there is a matching Mandible.stl that goes with it! My Skull Coin Box is going to need teeth!)

Actually... The Forum is having problems with .STL files again. The file came from here: www.thingiverse.com/thing:43591/#files But I had one uploaded as 'Test.stl' and it is attached.

What I'm hoping is somebody can tell me how to use Rhino or MeshLab or Blender to hollow out the skull. If I can just get it hollowed, I can slice it in two pieces and print up the little dowels to align the top. I've looked at all 3 of those programs, but I'm not even sure they can do what I want. And if they can, this is a pretty advanced topic to start with when trying to learn those programs.

[ssayer]

Blender is easy.
Import the skull.stl
create a sphere
Size it to what you want and put it in the skull
From the tool icon and it's a Bollean, Difference to make the hollow in the skull
Do the same thing for the dowels with a cylinder

[Roxy]

Blender is easy.
Import the skull.stl
create a sphere
Size it to what you want and put it in the skull
From the tool icon and it's a Bollean, Difference to make the hollow in the skull
Do the same thing for the dowels with a cylinder

Oh? OK!!! You make it sound so easy! I'll give it a try. Does Blender let me look inside something so I can see how thick the walls are that I'm going to end up with? And from what you described... I had another idea. Can I take the skull and remove most of the detail, and then shrink it a little bit, and use that for the Boolean difference instead of a sphere?

Update: Time to go watch a few tutorials! I can't even get the sphere I created to change size and be bigger... But I appreciate your High Level description of what I need to do!!!! I'll keep plugging away at it.

[curious aardvark]

have to admit everytime I've tried to modify an .stl file with openscad it wouldn't export.

I think you need a an ultra clean file to start with.

If you find an easy way to do it - let us know :-)

[Roxy]

have to admit everytime I've tried to modify an .stl file with openscad it wouldn't export.

I think you need a an ultra clean file to start with.

If you find an easy way to do it - let us know :-)

I've modified a lot of .STL files with OpenScad. But never anything super complicated with flaws in the .STL file. I'm on my 2nd Blender Tutorial right now and starting to understand the simple stuff. So I suspect it is going to be easier to modify the .STL with Blender and that will be useful in the future.

But as a side issue... I now understand many of the flaws that happen in .STL files and am toying with the idea of writing a program to fix those. If I can do that, then I can also have the program automatically hollow out solid objects like I'm trying to do here.

Back to the Blender tutorials!!!

[ssayer]

Oh? OK!!! You make it sound so easy! I'll give it a try. Does Blender let me look inside something so I can see how thick the walls are that I'm going to end up with? And from what you described... I had another idea. Can I take the skull and remove most of the detail, and then shrink it a little bit, and use that for the Boolean difference instead of a sphere?

Easiest way to put something inside of something in Blender is to center the object on the cursor and then center what you want to put into it on the cursor. That said, if you take the skull, make a copy, and shrink the copy... you can do all of that without ever moving the copy (and thus have it perfectly centered on the original). Now when you do your Boolean (I can't believe I misspelled it!) difference, the hollowed out area will be perfectly centered...

Update:

Time to go watch a few tutorials! I can't even get the sphere I created to change size and be bigger... But I appreciate your High Level description of what I need to do!!!! I'll keep plugging away at it.

To change the size of an object, select it and then click on the little plus on the upper right hand corner. There you will see dimensions that you can change (along with a lot of other good stuff)...

[Roxy]

Soon... I'll know enough to get it hollowed out and have the cylinders for the dowels. But first, I think I'll trim off the jaw and nose stuff so when I shrink it, I'm just dealing with the main area. So... In that case I guess I can't just do the two copies in the same place because I'll have to have one of them edited.

It seems strange they use right click to select things. That seems so backwards. But it is what it is. At least I can scale, rotate and move things now. I'll take your hint to center things on the cursor! What I'm thinking is if I can get the areas hollowed out, I'll just cut it at the right height in Slic3r and it will automatically flip the bottom piece so it can lay flat on the print bed to be printed.

I appreciate the pointers you have given me! It still is a long learning curve but they have given me good direction.

[jimc]

In rhino it would be the same step except you would slice the skull in half first to make your lid then make the sphere and boolean from the 2 halves.

[ssayer]

Soon... I'll know enough to get it hollowed out and have the cylinders for the dowels. But first, I think I'll trim off the jaw and nose stuff so when I shrink it, I'm just dealing with the main area. So... In that case I guess I can't just do the two copies in the same place because I'll have to have one of them edited.

But, once you've made the copy (in place)... write down it's x,y, and z location. Now move it to an empty area. From there you can trim it to whatever makes you happy and resize it. Then move it back to the location you wrote down and do your Boolean difference to hollow out your main skull.

It seems strange they use right click to select things. That seems so backwards. But it is what it is. At least I can scale, rotate and move things now. I'll take your hint to center things on the cursor! What I'm thinking is if I can get the areas hollowed out, I'll just cut it at the right height in Slic3r and it will automatically flip the bottom piece so it can lay flat on the print bed to be printed.

Personally, I prefer Netfabb basic for slicing an stl into two (or more) pieces, but like everything else, there is a lot of personal preference in this stuff...

I appreciate the pointers you have given me! It still is a long learning curve but they have given me good direction.

Glad I could help (even if it's only a little help)!

[Roxy]

So... I'm making progress! I can shrink the skull, and then cut off pieces of it that don't matter to form the 'hollow part'. But I need to learn how to close back up the big areas that I sliced through. And I need to learn how to gracefully remove things lift hanging like the eye sockets. I tried selecting pieces of the mesh and deleting them, but that is pretty painful. And if you look carefully around the eye sockets you will see where I missed and selected something behind them. When I deleted the vertices I made holes in the back of the skull!

But like I said... I'm making good progress. Blender is a very powerful program! I'm on the 4th tutorial. But the tutorials move so slow and talk about things I know I don't care about.

And I do understand what you mean by keeping track of the coordinates for things so I can position things correctly. I'm not to that point yet, but it is very clear why that is necessary.

UPDATE: Progress!!! I can close up the open holes I made and the big slice I took through it. Now I have to figure out how to remove all that stuff that is just hanging there!!!!

tmp.jpg