Hub help?

[Octo Proctor]

Hi guys,

I'm building a 4V geodesic dome house and am having the hubs fabricated by a local metal worker.

I've been to this site: http://geo-dome.co.uk/4v_tool.asp and the calculator tells me I need 6 five way hubs, 65 six way hubs, 20 four way hubs - around the base of the dome. for my radius of 16.5 feet.

The problem is that there are two types of six way hubs, and it doesn't specify how many of each I need.

Any help would be greatly appreciated.

Many thanks,

Brent

[Radu Sora]

Unfortunatly there are 3 types of 6 way hubs, of which 2 types become 4 ways because they lay on the ground. So you will need in fact 1 type 5 ways, 3 types of 6 ways and 2 types of 4 ways. Or you need a simple universal hub, not care about anything else but the lengths of your struts.
What is the design of your hub? Do you build on lumber or metal?

[Gerry in Quebec]

I've just deleted my earlier post because the heading on the diagram and tables that were attached said it was a "method 1" dome. In fact, the chord factors I listed were for the Fuller-Kruschke subdivision of the 4-frequency icosa dome. I'm uploading a new png file with the correct heading. The hub counts & letter identifiers are the same for both types of dome.

Good luck with your dome, Brent.

- Gerry in Québec

[Octo Proctor]

Wow, thanks Gerry.

I see it's a bit more complicated than I thought.

Forgive me my amateur confusion, but what are the angles between the struts in each hub? Or is it totally dependant on strut length? For example, in an ABCFCB hub, , is there a difference between the angle between A + B, or C & F? Or can I use the 60 degree spacing for all of them?

Also, would these measurements allow the dome to sit flush on the foundation, or would there be gaps?

Thanks so much for your help.

[Octo Proctor]

Thanks Radu, you probably just saved me a lot of wasted money:)

[Octo Proctor]

I'll be using lumber, Radu. After reading the site above, I thought that there was only one possible design, I didn't realise there was more than one way to put them together. The universal hub sounds interesting and much easier. Is there some disadvantage to using it? Do you know where I could find the angles for it or the others?
My apologies again for the amateur hour:)

On Thursday, April 13, 2017 at 11:23:57 PM UTC-3, Robert Clark wrote:

Here's a 4v that has just 4 strut lengths, but would still require 8 different hub types.

[Octo Proctor]

Thanks Robert, the simpler the better in my case. This one might be a winner. Do you know where I could find angles for the individual hubs?

On Thursday, April 13, 2017 at 11:23:57 PM UTC-3, Robert Clark wrote:

Here's a 4v that has just 4 strut lengths, but would still require 8 different hub types.

On Thursday, April 13, 2017 at 7:07:43 PM UTC-4, Octo Proctor wrote:

[Gerry in Quebec]

Brent,

Here's a link to an illustrated Excel calculator which, among other things, lets you find the radial angle between the hub connection points of any pair of struts. You just need to know the chord factors of the three sides (struts) of the dome triangle. The filename is Dome-angles-Feb-27-2017.xls 

https://groups.google.com/d/topic/geodesichelp/JOVMOQLeOj4/discussion 

If you read and post directly within the Geodesic Help site (rather than through e-mail), then you can simply click on the file and you will be given software options for opening or viewing it. The best option is usually to download the file and open it in Excel. 

- Gerry

- Gerry

[Octo Proctor]

A million thanks, Gerry. This is exactly what I need.

[Octo Proctor]

That would be fantastic, Robert.

I'm presently trying to figure them out, but it's quite daunting for a beginner to put them together.

Many thanks in advance!



On Friday, April 14, 2017 at 10:10:35 AM UTC-3, Robert Clark wrote:

Later tonight, I can post the radial angles and face angles for the dome pictured.

-Robert

[Octo Proctor]

That looks great. To be honest, I thought you meant the struts when you asked about lumber. I was planning on having metal hubs fabricated by a local metal worker.
One thing, how do the bolts attach to the strut at that angle? Do you need a separate connector for the wood?

On Friday, April 14, 2017 at 1:01:06 PM UTC-3, Radu Sora wrote:

Here it is. Can connect up to 12 struts at different angles, that means you can build also a spatial structure (2 layers interconnected like in Eden Project). You don't need angles, the struts self-align by their length. Drawback: never tested. I intended to use it this summer as a trial, but I would be happy if you would, because I have another project and lack the finances. I can assure you this hub is much sturdier than the lumber you will use.

[Radu Sora]

joi, 13 aprilie 2017, 20:18:58 UTC+3, Octo Proctor a scris:

The connection to lumber is quite simple : a square pipe (of 2") cut 4" length (or whatever width of lumber you use) with 2 holes drilled for the screws. On top of the pipe comes the lumber attached to the pipe with steel band (I don't known the term in English) from all 4 sides. I can make a sketch.

[Octo Proctor]

A sketch would be really useful if you have time. The hub is really clever by the way, I've scoured the internet for hubs and never come across one like it. Did you design it yourself?

[Ken Brown]

I local guy built a 50ft dome many years ago with a simple hub design.  As I recall, the hub was a radial-to-the-dome steel rod (maybe a big bolt?) with flat metal tabs welded around appropriately. The tabs fit into a single 6" saw-slot cut into the ends of 4"x6" lumber struts and then were bolted at right angle thru the 4" dimension and the metal tab in the slot. 

The dome was covered with custom formed fibreglass panels secured along the struts with aluminum extrusions, with a round weather cap over the joints at each hub. 

[Octo Proctor]

Brilliant, thanks very much, Robert. That should save me a lot of working things out.

On Friday, April 14, 2017 at 11:39:32 PM UTC-3, Robert Clark wrote:

Here's a drawing of the 33 foot diameter, 4v geodesic dome with dimensions.

[Octo Proctor]

Thanks kbrown, I'll see if I can find anything similar online.

[Ken Brown]

This is a bit similar to the idea I was trying to get across, I haven't been able to find a pic online of exactly what I was describing. 

<https://www.chiefdelphi.com/media/img/b04/b04c1c8f5f5b4d4dbfcd9c1ffa57c72b_l.jpg>

Ken G. Brown

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[Octo Proctor]

Thanks Ken,

That looks pretty hardcore:) It's given me some ideas.

[Ken G. Brown]

Well that particular Expo 67 hub was cast I believe but if you weld the required 5 or 6 tabs to a central solid cylindrical core, it should work. 

Ken

[Bryan L]

The domerama site had lots of different hub pictures. Should be good for ideas

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