Need Help Making Part from Spec

[Goaliexam]

I've been having some major issues generating an Inventor part based on the attached drawing (PDF).

As the filename says, the drawing is the profile of a dome, so the part has to end up as a 3d dome.

I try my best to follow the dimensions as specified, but when I use the Revolve tool on the half-drawing I make, it always leaves a "seam". This is the first part design I've run into in the past two years that I haven't been able to model, so this is driving me crazy.

I would really, really appreciate it if someone could make the part and then attach it to this thread or email it to me (maxcutler@gmail.com).

[SgtMillhouse648]

you might want to try extruding a cylynder, and then use the fillet to make the dome Ill try to make one

[Madison]

That dome is not spherical, it's elliptical.

Can you attach a screenshot of the sketch you're using and the revolved model? That'd help to see what you mean by 'seam' and to get a better idea of how to help.

Also, how do you know this is a dome? The drawing you attached doesn't provide enough information.

[Tristan Lall]

It's overdimensioned, as given, and due to roundoff error, some points aren't going to intersect perfectly. For example, the 18.250 and the 9.125 are redundant (theoretically, if the tolerances were different, this might be OK, but with none specified, it's too much). Also, tangent arcs have to be accounted for—see where you have 0.885 + 9.125 = 10.01? Since the radius is 10.011, it isn't tangent, meaning that there's a bulge there that isn't immediately obvious. If you mean those to be tangent, delete one of the three dimensions (because tangency is implied in conventional drawings). Also, it isn't clear whether you intend tangent radii where the 8.152 and the 10.011 intersect—if tangent, delete one of those dimensions, or a centre point dimension.

The whole problem with overdimensioning is that it allows a part to be interpreted in several ways. If they're overdimensioned but fully consistent, it's a matter of redundancy. If if they're inconsistent, like this one may well be, you risk producing different parts from the same drawing. (Aside: an overdimensioned, toleranced drawing will be inconsistent in all but the most trivial cases, because of tolerance stackup. This condition exists even when a global tolerance is implied, but not printed on each dimension.)

[Elgin Clock]

I have made this 2 different ways for reference (and no, not in Inventor but in Solidworks).

I'm guessing you made yours the first way I did and that's why you should have 3 sections actually - 2 seams.

Dome one (on left below) uses actual sketch components and tangent relations between them but indeed has 2 seams.

BTW, check your add up on the print of the .885+9.125 = R10.010 (not R10.011).
Or if those are ALL correct, I refer to dome 2.

Dome 2 (on right below) was made using only the origin as the bottom center of the part and using only the dimensions 9.125 and 11.685.

BTW, the green lines are what I actually sketched in and then revolved both of these.

Of course thinking about this more, there is one more possibility. The 1.828 dimension could be the base of the part (straight extrude up) and then a dome could be on top of that with a width of 9.125 and a height of 9.857 (11.685-1.828). Isn't it great to get drawings supplied to you with so many questions involved?? LOL Try accomplishing work in "the real world" under conditions like this, and oh btw throw in already unreachable deadlines while you are at it.
It's fun.. Trust me. I do this every day.

Originally Posted by M. Krass

Also, how do you know this is a dome? The drawing you attached doesn't provide enough information.

Ah, touche'.
LOL I'm guessing he was told it was one, cause that is an awfully weird extruded shape we have here if it's a plate or another type of extruded object.

[Goaliexam]

Sorry, I probably should have clarified a bit at the beginning:

Yes, I am sure it is a dome. I cropped out one of the corners, which showed it was actually the spec for an R2-D2 dome (I'm building an R2 for public demos to generate interest, as R2 is one of the few "robotic celebrities"). There is a club on Yahoo Groups that builds full size R2s based on the real thing and the real specs (measured and from insiders at LucasFilms).

As someone mentioned, the bottom 1.828 is actually a ring that the dome sits on top of, and which I didn't bother to remove from the drawing.

Attached is a screencap of the "seam" I was talking about. It doesn't appear when I render in Inventor Studio, but I'm still not convinced that it can't be avoided altogether.

[Morgan Gillespie]

Now if your building a replica of R2D2 for public demos you think the public will notice the fact that it isn't a perfect hemisphere?
About 99.99% of people will never notice, so why make it harder on yourself? Just use a perfect hemisphere.
Just this

[Goaliexam]

Well, that's true, they won't. And I'm buying a dome from the group anyways. But for my personal gratification and for the purpose of training younger team members, we are doing a full CAD of the thing, down to every last screw, all from the blueprints that we've been supplied. So, if someone can help figure out why this is happening, I would appreciate it.

I can make the part for you... If you're running the compatible version of Inventor. From there, you can see my steps using the browser bar, and that'll allow you to understand how to make parts of these types. If you're running Inventor 10, just shoot me a pm or something and I'll send you the part.

[Madison]

Originally Posted by Goaliexam

Attached is a screencap of the "seam" I was talking about. It doesn't appear when I render in Inventor Studio, but I'm still not convinced that it can't be avoided altogether.

I don't use Inventor, but I've never run across a seam like that appearing in Solidworks. I'd venture to guess that your sketch is wrong, however. It appears as if there's a divet or depression at the top of the dome which ought not be there and the edges at the lower sides are not perpendicular to the bottom as you'd expect from the drawing.

Can you show us the sketch with dimensions? I had no trouble creating the dome in Solidworks, as Elgin has done.

[wilshire]

even if you have a seam it shouldn't make a diiference in the end product once you go into Inventor studio and apply textures and specify materials in the renderings/ animations

the seam should not be an issue when modeling before post production work in studio