### Author Topic: elipse into a dome 3d  (Read 8365 times)

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#### rktect3j

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##### elipse into a dome 3d
« on: September 26, 2006, 11:19:15 AM »
I'd like to thank everybody who was helping me with my previous question.  Today my boss needs me to do something new though.

I have to turn an elipse within a 11'-3"x15'-6" rectangle into an eliptical dome in order to plot its points so our construction crew can build it out of plywood.  I drew the elipse but can't seem to make a domed elips out of it.  How should I tackle this.  Any thoughts would be greatly appreciated.  It is 39" tall with a 3 inch flatenned lip below that for a total of 42" tall.
« Last Edit: September 26, 2006, 11:20:34 AM by rktect3j »

#### Maverick®

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##### Re: elipse into a dome 3d
« Reply #1 on: September 26, 2006, 12:07:58 PM »
This is how I showed our carpenters to make an ellipse for an opening. It should get you started.

#### Maverick®

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##### Re: elipse into a dome 3d
« Reply #2 on: September 26, 2006, 12:13:58 PM »
A pretty good explanation is here

#### rktect3j

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##### Re: elipse into a dome 3d
« Reply #3 on: September 26, 2006, 01:43:36 PM »
A pretty good explanation is here

I do like this solution but I have one problem.  Your diagram shows that the width of the elipse is 10'-6" based on the height of 39".  I have 11'-3" opening with a 39" height.  How do I change this formula?  If A is always 1/2 B then I think I might have a problem.  B is 39".  Has to be.  ALso I am stuck with 11'-3" or 1/2 of it to 5'-7 1/2"
« Last Edit: September 26, 2006, 01:45:14 PM by rktect3j »

#### Maverick®

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##### Re: elipse into a dome 3d
« Reply #4 on: September 26, 2006, 02:01:45 PM »
Sorry.  I guessed that you wouldn't want the dome to go all the way to the "short" edge of the rectangle.

The height of an ellipse is whatever you want it to be. That is adjustable until you get too close to half the width then it just becomes a half-round.  So if you need the overall to be 11'-3" then you are correct, "A" would be 5'-7 1/2".

#### rktect3j

• Guest
##### Re: elipse into a dome 3d
« Reply #5 on: September 26, 2006, 02:07:06 PM »
Sorry.  I guessed that you wouldn't want the dome to go all the way to the "short" edge of the rectangle.

The height of an ellipse is whatever you want it to be. That is adjustable until you get too close to half the width then it just becomes a half-round.  So if you need the overall to be 11'-3" then you are correct, "A" would be 5'-7 1/2".

Thanks.  I think we may give this a shot.  I'll just cut sections thru my wireframe dome at 12" increments and then find each new focal point.  If I get A and know what B is I should be able to get each plywood section.

#### Cavediver

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##### Re: elipse into a dome 3d
« Reply #6 on: September 26, 2006, 02:52:47 PM »
I do like this solution but I have one problem.  Your diagram shows that the width of the elipse is 10'-6" based on the height of 39".  I have 11'-3" opening with a 39" height.  How do I change this formula?  If A is always 1/2 B then I think I might have a problem.  B is 39".  Has to be.  ALso I am stuck with 11'-3" or 1/2 of it to 5'-7 1/2"

I'm a bit confused here.  In the first post, you said the rectangle was 11'-3"x15'-6" , with a height of 39"  I understand that to mean you have to make an elliptical dome inside of the 11'3"(x) X 15'6"(y) X 39"(z) volume.  I'm probably missing something, but that doesn't sound like a simple elliptical dome.  It sounds more like a loft / revolve between two different ellipses.

#### Maverick®

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##### Re: elipse into a dome 3d
« Reply #7 on: September 26, 2006, 02:58:58 PM »
Oh I see.  I thought you would basically cut half ellipses and frame them with a center point. Like this.  My bad.

What are you going to finish the dome with?  That will look cool.

#### Maverick®

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##### Re: elipse into a dome 3d
« Reply #8 on: September 26, 2006, 03:01:34 PM »
It sounds more like a loft / revolve between two different ellipses.

Ahhh.  If that is the case that will be alot of math and head scratching.

#### Cavediver

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##### Re: elipse into a dome 3d
« Reply #9 on: September 26, 2006, 03:13:18 PM »
Ahhh.  If that is the case that will be alot of math and head scratching.

I don't really know if that's the case or not.

It's really not too bad, if you can cheat.  in the attached file, I created a solid of the "negative space" in SolidWorks and brought it into AutoCAD.  I have no idea how you would do this in AutoCAD though...

#### Maverick®

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##### Re: elipse into a dome 3d
« Reply #10 on: September 26, 2006, 03:15:08 PM »
I have no idea how you would do this in AutoCAD though...

Me neither.  I don't use Autocad.

#### Cavediver

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##### Re: elipse into a dome 3d
« Reply #11 on: September 26, 2006, 03:21:00 PM »
What do you use?

#### Maverick®

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##### Re: elipse into a dome 3d
« Reply #12 on: September 26, 2006, 03:23:52 PM »
Softplan.  Pretty much only residential and light commercial 3d .

#### MickD

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##### Re: elipse into a dome 3d
« Reply #13 on: September 27, 2006, 01:23:08 AM »
Can you use the long half of the elipse and 'revolve' it around the major axis?
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#### Kerry

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##### Re: elipse into a dome 3d
« Reply #14 on: September 27, 2006, 05:57:17 AM »
Confusion reigns supreme ..

How do you get a 3d dome from a plywood sheet ?

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