Onion dome

[Michelle]

ok heres my weirdest request yet...can any of you afficionados give any tips to a newbie on how to create an onion dome shape?

I have a crazy client who wants to put an indian temple shaped dome on an appx 25' wide porter-cocher..I can make the octagonal base and posts and even the fancy little finial bit I am lost on the "onion" shape bulbous dome...(to eventually be given to a metal fabricator to made out of copper (we think) and it would be fabricated remotely and shipped in pieces...any help appreciated!

[propstuff]

I'd bet EJ Armstrong is going to get all over this one. ;-D

but here's my suggestion:

Assuming you want an octagonal dome:

in Front view; draw the profile of the onion as a NURBS curve from the top of the pillars to the bottom of the finial. Don't go all the way to the tip of the point.

In plan view, duplicate the curve and rotate it around the centre point of the dome (not the end of the curve you drew) by 45?.

You now have 2 Curves in space.

Go to isometric view and LOFT between the curves to give you one face of the dome.

In top view Duplicate Array around the domes centre point to get the rest of the parts.

HTH

[ 02-20-2006, 09:09 PM: Message edited by: propstuff ]

[Michelle]

Actually I need a round dome (onion shaped) like those old orthodox churches...the base of the dome is an octagonal shaped rim joist if you will...but this may help as I soon a I figure out what Loft does- thanks propstuff...hope EJ still will help.

[propstuff]

OK,

draw the profile

use it to Sweep the shape.

This will give you the circular part which would presumably sit on top of your octagonal base.

If you want the octagon to "merge" into the circular part;

Start with the octagonal base plan profile.

Draw a number of circles at increasing heights that are horizontal sections of the dome.

Loft between them to get the shape.

[ 02-20-2006, 09:48 PM: Message edited by: propstuff ]

[Michelle]

Nicholas, Thanks for opening up a whole other world of surfaces for me..a great help!

Can one change the shape of an "onion" once its built without redrawing it from scratch?

[Andrew Bell@NV]

If you use a sweep to create your "onion", you can edit the sweep, which allows you to change the 2-D profile that is swept. The loft tool creates nurbs surfaces, with no "memory" of how they are created, so you would probably have to rebuild that. However, assuming you're just wanting to change height or diameter, you could use the Scale Objects command to do that change.

[Tom K]

ml,

In my past lives I've worked for companies that fabricated both porcelain and copper panels. And I've had to produce shop drawings for several domes.

Here is the reality, as far as I know it. You can draw your perfect onion shaped dome to your hearts content, but most likely whoever has to fabricate the pieces is going to do exactly what Propstuff suggested. It is almost impossible to fabricate a sphere, because the metal panels cannot be rolled in two directions. So what you end up with is a faceted shape that simulates a dome. So why not design it that way right from the start.

If you want to see some examples of what I am talking about go to the website pgbell.com and check out their gallery.