Carpentry advice - Geodesic dome

[AndyL]

Looking for some advice...

We're going to "overhaul" our greenhouse in the next few months, it's not really useable as-is, and since it's pretty much a ground up rebuild, kinda thinking of going different, something that 'fits' the space in the yard, and provides more room...

So we've been talking about the hippy solution

(stolen from geogrow )

Here's my issue, and why I ask... I've got my head wrapped around the math, But, the hub... I don't like the designs I'm seeing... The pictured one is Ok, but still not thrilled. 5 struts splicing together at one point, with screws at the very ends of 2x4's... Well doesn't scream 'built to last"

Some use steel plates/strapping, not thrilled by that idea either... Some make octagonal/pentagonal 'blocks' so your struts are single angle cuts - but again, shoving 20 some screws into a 8" block (through the ends of studs...) Doesn't seem the strongest...

Anyone have some thoughts on how to make these joints strong like an ox?

thanks in advance!

 

[RivennHewn]

Fab up some brackets out of 1/4" plate.

 

[Tink]

I'm not an advanced woodworker , but other joints you could look into are mortise and tenon,dado,spline or dovetail.

 

[AndyL]

Problem is you've got 5 mitre's coming together in a small area... At least in the conventional plans... M&T, not so workable, the others, really not intended for this type of construction.

My issue with steel plates is the limited surface area at the joint, and the fact that it's going to sit prow (suppose I could notch but then attachment of the material becomes more difficult, and we've somewhat weakened.

One thought was to cut some wedges to fill the angles - so I can get a few extra screws and a bit of PL400 in there.

 

[johnny mac]

Have you reviewed this option:
http://www.strombergschickens.com/prod_detail_list/Starplate-Dome-Kit

You mentioned you don't care for plates but thies one uses 4" bolts instead of screws.

John

 

[AndyL]

Did I mention I overanalyze everything?

when you go with that design, you loose the strength and stability (and weight carrying capability) because your no longer butting everything together, instead relying on thin steel - which even bolted through the weak end of the 2x4, wood ***** these days - it splits really easily.

and if it flexes too much, you get a tear in the steel which pits sharp edges against expensive wrapping material...

 

[srmofo]

Personally I would use 3/8 plywood (its kind of flexible and will conform to the shape) as a plate with some blocks of wood cut to fill in the voids. Hit it with some glue and use lag bolts with pre-drilled holes. Joints will be significantly weaker with out pre-dilling .

After that you could triangulate each joint with 2x4s a couple of inches from where they **** together

 

[kbs2244]

Wow.
Talk about a blast from the past!

Like you, I never like the end grain fastening.

A quick search showed up these solutions.

Make your own hubs
http://www.geo-dome.co.uk/article.asp?uname=hub_making

Cast AL hubs for wood 2x4
http://www.oldmoldy.com/Geodesic_Domes.php

Cast PVC hubs for PVC pipe
http://www.sonostarhub.com/sonostar-hubs.html

Simpson’s even maks one (steel gazebo connector) so you could get it at the local lumber yard.
http://www.strongtie.com/products/DIY/GT2-GT6-GTF.html

 

[racingtadpole]

Nail plates or truss plates.

 

[rlitman]

Wow.
Talk about a blast from the past!

Like you, I never like the end grain fastening.

A quick search showed up these solutions.

Make your own hubs
http://www.geo-dome.co.uk/article.asp?uname=hub_making

Looking at that site, it actually looks pretty easy to weld up. You just need a bunch of simple pieces, a lot of time, and some simple enough jigs.
And that design using the welded straps lets you put the connections in the part of the wood that you should be attaching to. I agree that screwing into endgrain, or one bolt across the very end of a 2x4 is a bad idea.

 

[Kevin54]

If you look at the design closely, even though you are not using very many screws, once you get the glazing panels on it will help tie it together. Each adjacent connector helps to beef up the prior connector. About the only ones I would really be concerned about is where the complete dome fastens to the vertical wall, which BTW, looks like an above ground swimming pool surround.

 

[Kevin54]

Take a look at this site. http://www.domerama.com/dome-basics/geodesic-dome-hub-connectors/ it has a buttload of different style of connectors.

 

[Bronson]

I helped a Buddy assemble a Dome kit last year. It had all pre-drilled pilot holes to pervent splitting. The finished dome is very rugged and so far no issues. Here is a link to the build.

http://www.motorcyclistcafe.com/forums/showthread.php?10949-Colora-Dome&highlight=colo+radome

 

[demographic]

Simpsons GT6Z gazebo connectors.

 

[chamoisfive]

From what I recall from years ago, the struts are held in a state of compression once fully erected, not under tension. That should be enough to allay your concerns over the way the hubs connect? I,m very interested in seeing your progress on this too. Had a similar idea for awhile for our yard too...... thanks for the threads

 

[AndyL]

I understand that's the theory, but that gets a little wonky when heavy wind / uneven snow loads are applied. When you start unevenly loading the structure - the stresses get funky (we were playing with it in ... gah what's the name of that software, solidworks?).

yeah I'll post once we sorts out the details, and get closer to spring and can start digging things up...

 

[Domerama]

There is a simple way to make a timber geodesic dome:

• Cut the ends at the angles shown in any geodesic calculator.
  
• Cut a piece of pipe large enough to have up to 6 studs around it
  
• Use heavy-duty metal strapping going through the piece of pipe and screwed to to the stud on opposite sides
  
• Cut small t-blocks connecting around the hub wich hold all the studs in the correct position AND strengthen the hub, hence the overall structure
  
• See the image attached!

 

[demographic]

There is a simple way to make a timber geodesic dome:

• Cut the ends at the angles shown in any geodesic calculator.
  
• Cut a piece of pipe large enough to have up to 6 studs around it
  
• Use heavy-duty metal strapping going through the piece of pipe and screwed to to the stud on opposite sides
  
• Cut small t-blocks connecting around the hub wich hold all the studs in the correct position AND strengthen the hub, hence the overall structure
  
• See the image attached!

Welcome onto the forum Domerama, interesting website you have there.
Masses of good information and well presented.

I'm assuming its your website judging by your username by the way.

 

[Domerama]

Thank you for the welcome. Yes, Domerama is my website.

I love this website! If anyone wants to build any geodesic structure, a yurt or other project, I'll be happy to help in any way I can on this forum.

This year I'm putting up more free building plans such as geodesic gazebos. But my dream is to complete the geodesic water wheel (a floating sphere you can paddle anywhere on water), when I figure out how to make it float better...

 

[demographic]

Thank you for the welcome. Yes, Domerama is my website.

I love this website! If anyone wants to build any geodesic structure, a yurt or other project, I'll be happy to help in any way I can on this forum.

This year I'm putting up more free building plans such as geodesic gazebos. But my dream is to complete the geodesic water wheel (a floating sphere you can paddle anywhere on water), when I figure out how to make it float better...

Just wondering, have you ever seen any geodesics made from plywood being joined by the "Stitch & Glue" technique thats sometimes used for boatbuilding?

After seeing a mate build a canoe using that method it occurred to me that it might be a good strong way to make geodesics. Might be quite time consuming though.

About eighteen years ago I borrowed a book from the library on the patents of Richard Buckminster Fuller and my then girlfriend copied the pages on her college photocopier, some pretty mad ideas in those pages but some quite groundbreaking stuff also. The tensegrity structures looked like they couldn't even support their own weight but were very strong.

 

[Domerama]

The closest I have seen to plywood dome is the traditional Fuller version



Here is a picture of a plydome and a list of books related to Fuller and geodesics:
http://www.buckminster.info/Ideas/02-TriWeave3wayDomePlywood.htm

There are also Sketchup 3D models of plydomes available.


For a new take on using plywood to build a dome, this is a must see:
http://www.abitare.it/en/architecture/plywood-dome-at-roskilde-festival/

 

[AndyL]

Fiberglassing the joints/hubs actually makes some sense to me... It's an interesting thought.

I get the impression domerama doesn't like my calling it the "Hippy solution" (going by Jan 11th post on his front page) - Sorry but the idea came from my self professed hippy friends... The kinds who go to burning man, which strangely almost every dome site references... Nothing wrong with Hippies, it's just an out of the box idea for some of us... I was trying to sort out how to build a 12x12 square that'll handle our climate, this just worked better

Gonna pull out the compound mitre this week, need a little shed in the backyard anyway, to hide the lawn tractor in. Might make a good test platform...

 

[Domerama]

I expect you are referring my post on how " Dome lovers are not hippies" ? That was fun to write up. Yes, it is true, we are stigmatized as "strut lovers" and everyone asks us what's our angle...

It is funny to hear the word hippie, because they made domes popular. What I hate about it is how they claimed it would solve so many issues, when in fact it caused many problems when not planned properly. Often domes were built with engineering issues as "troublesome, bro, the Man is totally uncool, it's harshing my mellow..."

Domes are not for all people or all purposes. If used for event domes, greenhouse, they will resist hurricanes and tornadoes, or be used as emergency shelters or small storage spaces; they are fun to build, incredibly tough. But for a home, it's going to be extra work.

 

[demographic]

Domes are not for all people or all purposes. If used for event domes, greenhouse, they will resist hurricanes and tornadoes, or be used as emergency shelters or small storage spaces; they are fun to build, incredibly tough. But for a home, it's going to be extra work.

Thats kind of the way I thought they would be, great for a different looking structure thats got the possibility to be very strong but square box shaped homes are quick and easy to do the finish carpentry in, domes look more awkward in several respects.

I would still like to make one at some point though.

 

[AndyL]

For a new take on using plywood to build a dome, this is a must see:
http://www.abitare.it/en/architecture/plywood-dome-at-roskilde-festival/

DOOD! That is awesome! Why do I have a feeling there's a whole lot more modeling in solidworks coming up... 4x4 plywood struts, would make for a seriously **** design...

 

[Domerama]

Here is a video with one of the builders/designers being interviewed:

Here is a video showing the construction of the structure:

The are images of the Roskilde dome everywhere on the web, simple Google it.

 

[Zeke]

Well Buckminster Fuller was around before any hippies were.

AFA the stamped steel connections go one could **** all the members with a little "carpentry." You don't have to cut the members short at a 90.

And one could make glue blocks with a protractor and a miter saw. Attach the members with biscuits, dowels or those oval dowels. Pocket screws from the block to member would be excellent.

 

[Domerama]

Since the 2 guys who thought up this design are engineers, I'll follow their recommendations

Too many underestimate the engineering realities such as the lift forces of winds. They apply their experience in woodworking or plumbing to domes, and that is a very big mistake. I have pictures of people building a 50-foot 3v, and their reasoning was that they thought they were only limited by the stud length. Same problem with metal conduit domes.

For example, people think domes are great against hurricanes and heavy storms, and it is true, except for one simple fact: If the base is not sealed against air coming in, it like a small hole in your windshield: only a question of time before it cracks all the way. A related issue is how well the dome is secured to the foundation. An event dome of 70 feet in diameter requires anchoring of 30-40 tons of weight around it, and that is a minimum requirement.

Here is a real-life example, the Eden project, the largest complex of biodome greenhouses in the world. The dead weight of the structure was not the issue when making the plans: the lifting power from the winds was.

So if you consider biscuits and screws, you may be in for a big surprise.

And as a side note, Fuller was often credited for ideas of others. He is not the science God many think he was. But he was the ringleader, the front man. If you research the people "behind" Fuller, you will find they were almost always the real genius behind projects. Don't go by the press release, dig some.

And it took hippies' drive and optimism to popularize domes to the masses.

 

[santagary]

I helped a Buddy assemble a Dome kit last year. It had all pre-drilled pilot holes to pervent splitting. The finished dome is very rugged and so far no issues. Here is a link to the build.

http://www.motorcyclistcafe.com/forums/showthread.php?10949-Colora-Dome&highlight=colo+radome

I've had our growing dome (Growing Spaces.com) up and running for 10 years now and grow produce year round at 7400' in the rockies. The 2x4's are held together with predrilled holes and bolts with washers and nuts. The triple wall polycarbonate panels (66 of them in my 22 footer) are screwed to the 2 x 4's then taped. We get over 160" of snow each year and considerable wind in Pagosa Springs with no movement or problems. It's the best 10k investment I've ever made. There's nothing like sitting out there during a blizzard and counting your tomatoes and orchids. Check it out. My only change would have been to order a 33 footer.
s

 

[Domerama]

Growing Spaces in Colorado does have a nice selection of domes. On the flip side, the cost per square foot is steep.

From my point of view, purchasing a plan and building one yourself could be a much better option. I've been meaning to make a comparison between homemade and kit offers. I'll do one for next week.

Here is the pricing right off their website:

22-foot Diameter:
Floor area………………………………………… 350 square feet
Height: 10 ft 10 in; Feeds 4-6 people
Cost:
($31.50 per sq ft) Classic Kit …………………………... $10,950(+taxes +shipping)


33-foot Diameter:
Floor area………………………………………… 850 square feet
Height: 14 ft 10 in; Feeds 8-10 people
Cost:
($23.50 per sq ft) Classic Kit…….…………………….. $19,950(+taxes +shipping)

 

[santagary]

Good luck building your own...it was surely beyond my level, skills and precision fabricating. I love mine and would buy another if I moved. Great customer service and attention to detail. They also have crews which build these (assemble) for you. I have other suggestions for those interested in building one of these for those wanting to ask on this forum or PM me. g

 

[thepolisher]

glue and screw toghether using galvanized screws and PL premium ,joints will last a long
time but dont get glue on your hands or clothes that lasts a long time also . good luck with your project.

 

[Zeke]

And it took hippies' drive and optimism to popularize domes to the masses.

I think it took the "Whole Earth Catalog."

http://www.wholeearth.com/index.php

 

[mmack66]

Did I mention I overanalyze everything?

when you go with that design, you loose the strength and stability (and weight carrying capability) because your no longer butting everything together, instead relying on thin steel - which even bolted through the weak end of the 2x4, wood ***** these days - it splits really easily.

and if it flexes too much, you get a tear in the steel which pits sharp edges against expensive wrapping material...

http://www.domerama.com/fabricating/diy-projects/assembly-of-a-geodesic-dome-greenhouse/

Once you have the geodesic structure put together, there is no flexing, and there won't be a big enough load on the structure, in normal situations, to cause it to fail. That's the beauty of geodesic domes, they're strong as hell with minimal material.

 

[Domerama]

A geodesic dome is usually a little wobbly until the last strut is put into place, then it's surprisingly strong, able to support great loads.

And when you add panels to cover the dome, this entire structure becomes even more sturdy.

But keep in mind the exerted pressure is downward and outward. This means your riser wall should be very well secured to the ground. If I were in a heavy snowfall area, I would add a couple of metal straps around the wall for additional support and a good amount of ground screws (like those for tents) unless you have a concrete platform, then I would have rebar stick out from it.