Mechanical part, simple but complicated to model!

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1

Hello all, I am modelling a mechanical part, that is basically an empty hemisphere that has some thickness, and a big hole on the side at 45 degrees.

What I did since now… I made a sphere, I put another sphere inside it, just a little less radius than the other, and made a boolean operation, I obtained an empty sphere (like a ping pong ball but thicker), then I went into edit mode and selected all the lower vertices and eraser them. Then I connected all the lower points, creating faces, to close and connect the inner and outer surface. I obtained a sort of “shell”, shaped as an hemisphere, of a certain thickness.

Now I have to make an hole on the side. I put a cylinder at 45° that go through the shell, but the boolean operation wont work! It says that the object must be closed, but apparently everything is clean and there are no opened holes. I played a lot around the mesh but I didn’t find any way to make it work…

Then I tryed another method, I deleted some faces on the side, put a circle where there will be the hole, and connect the hemysphere faces to the circle, but the result of the rendering is very ugly and choppy.

I can’t find any other way to make it look good, anyone can give some suggestion on it??

I love Blender and I use it often (I used to have 3D studio before but I decided to stop to use it, also for the price that is quite a lot) but sometimes makes your life difficult in doing simple things that in other apps is a matter of 5 minutes.

Thanks in advance for any useful suggestion.

UPDATE: I selected the non-manifold and fixed them, now the boolean operation don’t give the “closed object” error, but just don’t give anything, I see that Blender execute the operation and gives 3 meshes, the 2 original and the result, but the final thing is just an union of the two objects, even if I did a difference :frowning:

PS: In the attached file you can see what i was able to make until now.

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2

Did you see this post? It was 2 down from yours.

http://blenderartists.org/forum/showthread.php?t=66970

:slight_smile:

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Yes, I saw after I posted and I tryed immediately, but unfortunately seems that the bollean is quite a buggy feature :frowning:

4

Maybe you could do this:
add hemisphere > make sure there is a loop at the position you want your hole at> create hole > rotate entire sphere 45 degrees> create cut horizontaly( with shift k, and choose exact line) > delete bottom half.> extrude faces inwards to give it thickness.

Something along the lines describe above should give you the desired result. I am on a work laptop right now and can only try it myself next week sunday when I get back home.

5

Yes, seems to be a bit buggy. You might also want to try reducing the
vertices in your cylinder (guess it makes the math easier). You can touch up
the subtraction after it is done.

hope this helps :slight_smile:

6

How about doing it this way:
1.From the top view, (numpad 7), create a UV sphere.
2.Select the topmost vertex, hold down the Ctrl key and click the numpad + key to expand the selection until you have the size of the hole you want.
3.X key or Delete key to delete the vertices.
4.Tab key to switch to Object mode, numpad key 1 to switch to front view. Rotate the sphere 45 degrees.
5. Switch back to top view (numpad 7) and create a plane. Tab back to Object mode. If you didn’t move the 3d cursor, the newly created plane should cut across the sphere’s midsection. Move the plane a bit along the z axis. (The Knife tool script gives an error if the plane is exactly in the middle of the sphere)
6.Open the script window, go to Object/Knife tool.
7.Select the sphere, hold down the shift key and select the plane. Both should now be highlighted. Click the cut.
8.You should now have two additional objects – the top and bottom sections of your sphere. Move the objects around to see them.
Look for Cambo’s solidify mesh script to add thickness to your sphere.
http://members.iinet.net.au/~cpbarton/ideasman/

7

I was able to come up with this using mesh editing on an Icosphere:
http://img103.imageshack.us/img103/7480/mech7wm.png
Icosphere at Subdiv 2 with the appropriate faces deleted & all remaining faces extruded & scaled along normals. Subsurf at level 3 & edge edits for the sharp edges.

Let me know if you want the .blend or a step-by-step later.

Hope this helps!

8

I just tried grafix’s method, and it works fairly well also.

The method I had used before results in a cleaner mesh, but the other one gives more control over the size and position (angle) of the hole.

So there is a trade-off . . . just depends on your specific needs arrakis.

9

Thank you guys very much for all the suggestions.

I tried to develope the piece following all the methods suggested, but I couldn’t be able to come to a good result.

As you can see in the attachment, picture n.1 and 2 was made following grafix’s method (using also the “solid mesh” script), but I couldn’t do more than what you see. I restarted all from the beginning many times, tried to clean the meshes, remove doubles, do ctrl+n, even exploring face by face to see if all is ok, but the best result that I could get until now is that one you can see. Everytime there is a new problem, ugly faces, etc.

In the picture n.3 I followed Cire’s method but the hole is not really a circle, it is more a like large ellipse, and it must be precise since the hole will have another piece going inside (in different renderings) and once you put a cylinder inside you see the difference.

I will try to fix them and maybe try different approaches too, but the production time for that single piece is really unacceptable (maybe for my my not big knowledge of Blender).

Btw as an ex 3ds max user I’m a bit frustrated, with it I would have finished already and be in another project. Not that I want to make criticism to Blender (that I love and suggest to others too) but when are at work and you see the hours flying, trying to make some very simple object, you start to understand the people who pay thousands $$$ for such softwares.

Thank you again for all your very useful and interesting suggestions. I understood that each time I have to develope something in Blender I will need to exercise my mind in “workarounds” :slight_smile:

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Senza-titolo-1.jpg800×254 10.4 KB

10

I think that’s it . . . :smiley:

But remember, once you figure it out, that new knowledge will make all future projects easier!

That’s probably because you’re already familiar with Max’s tools & workflow. I’m an ex-Max user as well, and I can tell you it’s no magic solution . . . plenty of frustrations & workarounds (esp. when new to the software)!

If time saved is worth that premium, then yes (often the case in a professional environment). But Blender can produce the same level of quality in a similar amount of time, in the hands of an experienced & creative user . . . for FREE!!!

Glad to see you realize that. And exercising your mind is not a bad thing, right?

With your questions, the suggestions of others, my own experimentation & about a total of 2 hours (including the earlier stuff) here is your model:

  • UVsphere with cap removed & rotated 45*.
  • Knife (exact) at mid-section & mesh editing to clean up the bottom edge.
  • All faces extruded & scaled along normals (Shrink/Fatten).
  • Subsurf level 2 & mesh editing for sharp edges at the rims.
    No Booleans (hate them), no scripts (not needed), and no Max (too expensive).

Let me know if you would like the .blend or more info so as to recreate the model.

11

http://rapidshare.de/files/20312013/hemi.jpg.html

Ok, nothing fancy here.
What I did was start with a cube—>subdivide twice*—>to sphere 100%.
Select bottom half and delete verts.
Object mode—>duplicate—>Escape—>scale to 1.1
Join objects.
Close faces on bottom of hemisphere (actually took the longest to do).
object mode—>insert mesh cylinder 16 verts—>scale and position.
object mode—>select hemisphere and apply a boolean difference modifier
to it with the cylinder as the object.
delete cylinder.
No textures, smoothing etc., just trying to show a technique

*maybe three times, err,I was having a beer!

12

Thank you a lot guys for all the help! Finally I was able to make it :slight_smile: The only thing is that slightly segmented border on the base, that I couldn’t figure out how to make it look like a perfect curve. Anyone knows how to get rid of these? I tried auto smooth but no difference

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13

arrakis,

Out of curiosity, what tools/methods does max have that would have made this so much easier than using blender?

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Clean & efficient booleans :slight_smile:

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For my version, I had to merge vertices to get rid of any tris. If you used Subsurf as I did, quads are better. Just be careful to keep the vertices of the bottom edge aligned to a common plane, and try to space them as evenly as possible along the curve for a smooth result.

It’s not hard and does not take long, if you use the 3d cursor to snap your merged vertices according to the existing topology. To save time, just do half and mirror the clean side.

16

Thank you Cire, I followed your suggestions and I was able to obtain a good result.

I was not very sure on how to proceed, but I made a try on a small part and I saw that I was going on the right direction, so I made an half “clean”, deleted the other half and then I applied a mirror modifier.

I don’t know yet about 3D snap and topology of Blender, the method that I used was to delete the unnecessary vertices and then remake the faces trying avoid at most to make triangles.

I thought, for the help of all the non-expert users (like me), I could post here the “before/after” picture :slight_smile: Showing the edit mode screen and the render of both situations. I hope it will be helpful to others.

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bef-aft.jpg800×741 116 KB

17

Happy to help . . . your mesh turned out really good.

By that I just meant using the 3d cursor and existing vertices to move/create vertices in the right place so as to maintain the smooth shape of the base sphere.

Keep up the good work!