How the H*** Do I Do THIS

Discussion in 'How Do I...' started by Gandolf50, Mar 23, 2019.

  1. Gandolf50

    Gandolf50 Researcher of obscure between war vehicles... Moderator

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    Moved from UX Thread.
    I was asking @goodduck how he creates his model skeletons ( for structure and stability) in Rhino.
    I had tried many different ways Boolean Operator, cut, trim and many others but basically gave up, thinking that it just wouldn't work with the objects I have to deal with on assignments.

    If you follow have followed that thread then you know there is his solution and my attempts to follow.
    His solution works! Some of the time, and most of the time, but here are some things I have found that occur when following his example.

    First off, he created his model in Rhino, which makes a big difference. Models that you gather from the net, or create in other software may or may not work. Rhino has its own definition of what an object mesh is. When you load a .obj mesh, Rhino says its a mesh but doesn't treat it as a Rhino mesh. Commands that work on RM (Rhino Mesh) do not work as they should on and OM (Object Mesh), that includes .obj, .fbx, .3ds or any other mesh not created inside of Rhino. So there are some things you just CAN NOT DO.

    On to what happens or what I have observed in the wee hours of this morning.

    Wanting to create a skeleton I followed @goodduck and knowing that a mesh cannot be trimmed if there are gaps or any part of what you are cutting cannot be within another part not selected as a cutter.

    HE-111_1.png

    Example, Want to create a frame to support the skin in the tail section of this HE-111. Position is EXTREMELY important in this case as it has a full interior, forward of where I placed this CP (cutting Plane). So I placed it just aft of the interior walls and just forward of the belly greebles.
    Below I added a second CP aft of the first and one vertically down the center line ( the vertical one failed completely as it touched too many things and I did not realize at this time I could have shortened it, as I thought it HAD to extend beyond the CM (cutting mesh).
    HE-111_2.png

    I removed the Vertical on and added a CP horizontally, shortening to not touch anything outside the CM.

    Cut-Planes.png

    I used the function MESH TRIM to TRIM all of these CP to the inside skin of the tail section. First the Horizontal then the Verticals. ?? did not go well on first try and on subsequent tries. Several things happened. Forward CP did not do anything , second worked perfectly ? as it cut the CP and removed all the outer section with one click and the third cut the CP but left it attached to the inner section.
    As you can see here.

    Horiz-AfterMesh-Trim.png
    This shows that it traced the inner surface of the skin but did not cut it. Using EXPLODE it separated it just fine as shown here.

    after-Explode.png

    I then dealt with the verticals... I found out that if a just left-clicked the vertical CP it might work, but leave the outer parts still attached, or it might cut part and leave behind sections of the outer parts, or it just worked. After working on it for some time I found I had to hold down when left-clicking then it would cut and remove outer section. As shown here...

    afterMeshtrim.png

    Then I used Dup-Border to get an outline of the parts. That worked just fine.

    Dup-Border.png


    Trying to offset gave me problems as all would work except the aft vertical, it just would not offset a curve or it would only do a small section, fixed that eventually by changing the tolerance from .001 to .1 and then it worked, as seen here...

    Offset.png

    So for at least I finally managed to get-er-done (hmm) just need to delete the outer curves an flatten them for a top view to print... first I have to figure out how to create the halfway slices so that they will mortice together. I think I will do another doing the same thing in Blender, as many many people use it and it is FREE for all.
    mysteroid likes this.
  2. zathros

    zathros -----SENIOR---- Administrator Moderator

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    If you take the .obj mesh, and brake into small pieces, you can convert it into a curve network. Tis takes a lot of processing power, that is why I recommend braking the model into small parts. Then Rhino sees the "Mesh", and you can work with it, and like I wrote in that post, by the time I am done, there is nothing left of the original .obj file, but it served as a guide. The Commands that work with Mesh's are under the Curve drop down menu. You can even duplicate the Mesh edge, if Rhino sees it.

    I see many extra steps in this method, and if you know what you are going to work with, as to the thickness of the paper, it is much easier to cut up a Copy of the fuselage, or even project a line onto it, and use that as the cutting tool, then reduce the shape of the former under Transform. You guys seem to be doing this the hardest way possible.It certainly isn't saving time. Then again, maybe I hae no idea of what I am looking at. If I had that file, I could show you how I would do it, but I think you understand what I am writing. ;)
  3. goodduck

    goodduck Active Member

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    When you can't cut, that only means that you got control points that are not connected. So, you have to go in close up to connect all the unconnected control points one at a time, it can not have an opening. Making sure all the center cp are line up center will make your cut easier too.
    All the model no matter how good they look to you, once you go in close up to check the cp, you'll see none of them are watertight, that just how things go in our business.
  4. Gandolf50

    Gandolf50 Researcher of obscure between war vehicles... Moderator

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    In RHINO there is almost NO function that will work on a .obj mesh. Nothing I can find except what we have already discussed and a few that I know of, like Curve from objects. or meshtonurb. If you do use mesh to nurb then YES you can do all that you talk about. You can't even BREAK an obj if it wasn't created that way... if it is a solid .obj and you try to split disjoint mesh, Rhino just laughs at you! I don't see anything that will work simpler without rebuilding the mesh in Rhino and that is not time-saving what so ever.

    Obj.png

    In the above after exporting the original Rhino mesh as .obj and importing back. Trying to use a function on that .obj you can't even select it, Rhino won't let you and these are SIMPLE things... I deal with way more complicated stuff, like the last file 232,577 vertices/110,808 faces/ 120 objects for ONE PLANE! and that is simplified LOW POLY Version!!!
    Last edited: Mar 23, 2019
  5. goodduck

    goodduck Active Member

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    ? sent me a part and see if I can cut it.
  6. Gandolf50

    Gandolf50 Researcher of obscure between war vehicles... Moderator

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    Yep, I get that...but when it is a truncated cone, for instance, there should not be any reason whatsoever that it does not work. I think it is just a glitchy system when using a .obj as I can do the exact same thing 3 times and get different results a small percentage of the time. Or Rhino has been on here for long enough it could do with a new re-install, which could just be the case, who knows!

    The file itself is an 8 MB .fbx just the mesh alone. I can't share it as it was an aircraft for Warthunder and they are nasty about there stuff getting out.
  7. goodduck

    goodduck Active Member

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    I don't want a your whole model I got more than enough of my won already, just the part that you can't cut so I can see why. If you can get it Rhino, you can cut it.
  8. zathros

    zathros -----SENIOR---- Administrator Moderator

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    I understand. As I stated earlier ( or the other thread) Rhino doesn't see ..obj files for anything except converting the mesh to curves, or getting the control points out of the .obj file. That's why I don't work with them anymore, it's just plain easier to make your own mesh. Also, Rhino only works with Version 8 .obj files, forget about the later versions, the newer files have to be saved into Version 8 to work at all.