Building a 4 frequency 32' diameter dome

Mr.? · Post by **Mr.?** » Sat Jun 20, 2009 12:52 pm

I'm pretty new at this whole dome construction thing, and I'm looking for some advice from someone who has had actual experience with constructing and assembling a 32' diameter, 4 frequency geodesic dome made of 3/4" EMT.
I've looked through almost every online resource I can find looking for specifics on what sized bolt I should use but I can't find anything specific on a dome of this size. My first dome was a 16' diameter 3 frequency dome, and 1/4" steel bolt worked just fine for that one; I'm pretty sure I'll need to step up the size the bolts on this one, but would like to hear from someone with experience before I drill.
HOLLY CRAP THAT'S A LOT OF STEEL!!! I cleared out two of my local Lowe's and still had to go to a third store to complete my purchase of 140, 10' sticks of 3/4" EMT.

stargeezer · Post by **stargeezer** » Sat Jun 20, 2009 7:27 pm

I just did some checking from my spreadsheets on domes, and with the 140 sticks you have, you will still need to go back to the store. It will take 170 sticks and you will need to reduce your dome size slightly below the 32' you specified. As far as the bolt size, the EMT is the weak link, that same 1/4' bolt should work just fine, but if you are nervous, 5/16" and 3/8" are viable options, any bigger and the hole weakens the EMT too much. Your struts will be significantly longer than your previous dome, make sure you only put weight at the joints, never in the middle of the strut.

Mr.? · Post by **Mr.?** » Sat Jun 20, 2009 7:49 pm

Thanks Stargazer!.. My stepfather thinks the 1/4" in a higher tensile strength would work fine as well... 30 MORE!!!! Christ whats another 30 at this point? I looked it over several times on desertdome.com and counted my cuts up pretty accurate... Maybe our calculations are different? I'll let you know tomorrow night. I'm about half way done cutting them right now, and will get the rest out of the way tomorrow after noon! Check back and see if I'm cursing or kicking my heals.

stargeezer · Post by **stargeezer** » Sun Jun 21, 2009 8:07 am

30 "A" struts
30 "B"
60 "C"
60 "D"
70 "E"
90 "F"

340 Total

If planned properly you will get 2 struts per stick

340/2 = 170

If you don't plan ahead, some sticks will give you only one strut, and your stick count goes up.

Ugly Dougly · Post by **Ugly Dougly** » Sun Jun 21, 2009 8:45 am

Four frequency?

Is that all you got?

stargeezer · Post by **stargeezer** » Sun Jun 21, 2009 9:04 am

My Error.

For some reason I had too many "F" struts in the spreadsheet, there should only be 30, not 90!!!

Sorry for the confusion.

stargeezer · Post by **stargeezer** » Sun Jun 21, 2009 7:19 pm

My numbers were really screwed up. Most people have been more interested in 3v domes, and I have a spreadsheet to minimize scrap, and I had checked that out very well. I also modified it for higher frequencies, but I must have forgotten to double check my entries. My apologies for any confusion.

I will update my previous post with corrected data as follows:

30 "A" struts
30 "B"
60 "C"
70 "D"
30 "E"
30 "F"

250 Total

If planned properly you will get 2 struts per stick

250/2 = 125 sticks

robotland · Post by **robotland** » Sun Jun 21, 2009 7:29 pm

I routinely use 3/8" Grade Five bolts (by the pound, from TSC) for my domes....Anything smaller I find increases the Drop Factor significantly, and the bigger the hardware is the easier it is to work with while gloved or just with them coated with slippery playa dust. Also a common size for threaded eyelet bolts, which I generally place in the middle of my pentagons for hanging hammocks or rigging from.
I also make my holes 1/2", to reduce binding during installation and give just a wee bit of Slop Factor to the fit.

Way to go, ? , making a Bigass Fun Dome! I'd like to come visit it and marvel at your patience!

Mr.? · Post by **Mr.?** » Sun Jun 21, 2009 8:47 pm

Robotland: Way to go, ? , making a Bigass Fun Dome! I'd like to come visit it and marvel at your patience!

You are not just invited... You are required to visit now! Two domes, three scaffolding towers the highest 26'. I've got a regular old sweat shop over hear with my aunt and mother cranking out three giant shade sails made of nylon spandex. Renting a stage lighting system for night and a water misting tent for the day. Our camp name is Spontaneous Planning Camp, and my goal is to create a place to share camp ideas and designs. I'm going to have two shelters on display with a print off of plans and cost for each. The two designs that I'm shower are a tensgritity made of 2x4s and rope, and quonset made of PVC; both are very easy to transport, cheap and work fantastic. I'm trying to make an "Eplaya" on the playa!
Come share your designs for what ever you enjoy. I just found out about hanging your fruit in nets last year!.. That was fucking great.. Can't wait to hang all my food this year!

Mr.? · Post by **Mr.?** » Sun Jun 21, 2009 8:52 pm

Stargrazzer, I was thinking about you all day today. When I finally got done cutting the pieces I counted them twice to make sure I wasn't tripping!... Hehehe Like I said I'm glad you were wrong, cause another 30 sticks might of broken my spirit!?!... NOT
In a side note I think I be about to break my 6 ton hydraulic press and I've only done 140 ends with it.

aranryan · Post by **aranryan** » Tue Jun 23, 2009 12:36 pm

Stargeezer,

You mentioned you had spreadsheets that help minimize waste. I've built a 15' 3V dome last year (which I believe wasted more than I should have) and would love to get ahold of a tool that helps with variable sizes. Would you be willing to share those spreadsheets? I'm sure a million e-playan's would love it.

Is it excel?

stargeezer · Post by **stargeezer** » Tue Jun 23, 2009 8:40 pm

For a 15' diameter dome, you should have used 40 sticks for a 3/8 dome and 55 sticks for a 5/8, each making 3 struts. To minimize waste, you could have gone to 15' 7 5/8", but that is the limit with 3 struts per stick. Going to 2 struts per stick, the maximum dome size is 23' 10 1/2".

Where it gets real interesting is when you are making two domes, and you allow the sizes to be different just to minimize scrap. I did the numbers on one pair this way, and I think they came out pretty good.

As far as my spreadsheets, they make sense to me, but I have had fun trying to explain them to others. Rather than give them out and create confusion, I would rather provide information when requested, and I try to respond fairly quickly, for the fastest response PM me so I get alerted to a message via email. I was most curious about a 6V myself, so I checked that one out pretty well, and I have given people numbers for a 3V on several occasions and have had no complaints. I am currently checking my 4V and 5V versions as I found a small mistake over the weekend.

For a 3V dome, I will say that the optimum sizes are, 23' 10 1/2" and 15' 7 5/8". These numbers are for 2 and 3 struts per stick. If you want more struts per stick, the dome size just gets too small to be reasonable. If you would like me to run a particular frequency or dome size, I would be glad to help. I will also give you the cutting combination to make these happen. It is pretty easy to figure the best cut combination when working with 2 struts per stick, but as that number goes up small changes can really effect dome sizes, and this is really evident on medium sized high frequency domes. I really enjoy the challenge of multiple domes as this makes for an interesting puzzle.

Mr.? · Post by **Mr.?** » Wed Jun 24, 2009 8:41 pm

Ok, I've got a few more questions. What do you guys prefer on bolt types; carriage bolts or hex bolts? I've landed on 5/16 3" bolts for all the connections. Is that too long, should I go with 2 1/2"? What about my bolt length on the lower part of the dome? I don't want long bolts sticking out 1", after getting tightened, on the lower part; or do I? I don't want anyone impaling themselves... or do I?... Hummmm
I feel that I might of pressed the wrong length on one size of struts. The length is fine on all the struts, and the holes are at the correct lengths; I'm just worried about some of the struts not having enough flat surface at the connection. Is this going to be an issue because on a lot of them the bend angle is almost over the hole?
To help me with my presses I've cut a steel die for my 6-ton hydraulic press that puts a curve on the crimp. There is a stop in the back of the press to feed exactly 1 1/2" from the top of the curve to the end of the strut. When I was smashing the ends one size the stop was off by almost a half inch. When I drill the 1/3" hole in the flattened ends, the hole almost buts right up to the crease... Is this going to be an issue during assembly? Anyone else ever done a donkey move like this? I started trying to repress them, but with the curve of the press the strut slides out ever time pressure is applied. I sucks if I have to remake them cause this was the 2nd largest number of struts (60).
PS... I broke my 6 ton hydraulic press tonight. It takes 500 presses for this dome, that's 250 struts, on each end there is one press hence the 500 presses... My hydraulic 86ed on press 499... Thanks Harbor and Freight.

Mr.? · Post by **Mr.?** » Wed Jun 24, 2009 8:54 pm

Here is my die that I cut and fabricated, and the press I bought from Harbor and Freight. Between that and the welding I had to do on the press itself I should have just dropped the extra $100 and purchased the 20 ton press.

[img][img]http://i47.photobucket.com/albums/f187/ ... ion089.jpg[/img][/img]

[img][img]http://i47.photobucket.com/albums/f187/ ... ion025.jpg[/img][/img]

falk · Post by **falk** » Sun Jun 28, 2009 3:46 pm

I have detailed photographs and information on building a dome this size.

Points to ponder:

It takes 250 struts to build a hemispherical 4-frequency dome. I was able to make these from 125 10'-long pieces of 3/4" emt. If you add doors to the structure, you'll need more.

70 "A" struts
60 "B" struts
30 "C" struts
30 "D" struts
30 "E" struts
30 "F" struts

(My A/B/C/D/E/F designations may differ from others)

I used 1/4" bolts to build mine. They all worked fine except for the one at the top, which was bent every time, mainly due to the fact that I suspend the entire dome from the top while building it. If I had it to do all over again, I'd use 3/8" bolts, but if you use high-quality 1/4" bolts, you should be fine.

I used hex-head bolts, but carriage bolts would be easier on the cover.

A 32' dome optimizes the use of metal, which is why I assume you chose that size. You should stop and also decide how you'll make the cover before you finalize your dome. You may find that a design that optimizes strut material is wasteful of cover material.

Photographs of my dome being constructed: http://www.efalk.org/OasisDome/photos/

"Case study" from the geodome program — shows a 32' dome being designed. http://geodome.sourceforge.net/example.html

Assembly instructions (pdf): http://www.efalk.org/OasisDome/instructions.pdf

Mr.? · Post by **Mr.?** » Sun Jun 28, 2009 7:19 pm

That is fantastic stuff Faulk thank you very much! I'm going to take another look at the cover instructions after I send this reply, but it's very helpful and refreshing to see such detail descriptions, suggestions and pictures. The first dome I made was only 3V 16' diameter, and we had to put it together from top to bottom. I'm a little apprehensive about construction from bottom up on this 4V dome, but I'm using three sets of scaffolding and two 14' ladders. You have never assembled your dome from the bottom up? I'll let you know how it goes, and from what I saw so far I think I'll copy your design on the cover?
Please come and check out our camp this year. Spontaneous Planning Camp. I've got three different designs for structures (Tensegrity, Quonset and dome) to display, and show people how to construct them. I've documented the making of this dome very well, and I'll have a "science fair" type board showing each step of the process. There will be a brief description of said domes assembly, and a table with a model of a 3V dome for people to assemble. I'll have a board of stuff for other people to share there designs of anything BM related. i.e. evaporation ponds, showers, tents or what ever they want to share.
Come find us

muchas_cabras · Post by **muchas_cabras** » Tue Jun 30, 2009 11:14 am

Mr.?, I almost purchased the same 6 ton press from Harbor Freight but changed my mind at the last minute and went with the 12 ton instead. The 6 just looked a little too Rube Goldbergian to withstand very much use. Ironically the pump assembly on my 12 came apart after about 150 struts and I had to repair it with a couple of 5/16's bolts. The uprights also bow noticeably when it's under load so perhaps the 20 ton is the way to go 'specially if you're gonna use 1" EMT.

The jig I made to crimp the ends of my struts looks pretty similar to yours but I was maybe a little more anal with the design.

Mr.? · Post by **Mr.?** » Wed Jul 01, 2009 6:04 am

Show off!...
Just kidding.. Nice design you have there. Did you have it machined or did you do it yourself? How did you get the curve so smooth and nice?

muchas_cabras · Post by **muchas_cabras** » Wed Jul 01, 2009 12:38 pm

Thanks for the compliment.. I actually spent about as much time constructing the jig as I did crimping the ends of my conduit.

I had a 6" X 6" piece of 3/8" steel plate laying around so I bored a 1 1/2" hole in the center then split it down the middle with a chopsaw. This gave me the top and bottom sections of my die with that "smooth and nice" curve you mentioned. I initially intended to try and sell a few domes to recoup my expenses and I wanted a jig that would be fast, precise and consistent. The price of EMT went through the roof last summer however, wrecking my plans. Everybody thinks geodesic domes are cool but finding someone willing to fork over the $$ it now takes to build one is tough.

Token · Post by **Token** » Wed Jul 01, 2009 2:07 pm

If only you had a hole punch in that die you could press and punch the hole in one operation ...

Mr.? · Post by **Mr.?** » Fri Jul 03, 2009 1:57 am

If you can manage the hole punch why not go the extra distance and get it to cut the ends rounded, much like the crimps curve?

muchas_cabras · Post by **muchas_cabras** » Fri Jul 03, 2009 10:15 pm

Mr.? wrote:If you can manage the hole punch why not go the extra distance and get it to cut the ends rounded, much like the crimps curve?

These guys make dies that do just that.
http://www.vogeltool.com/sample_parts.html

This page (scroll down 3/4 of the way) has a "custom feed-through double flatten, radius trim and pierce die" that even does 2 pipe ends at a time.
http://www.vogeltool.com/custom_dies.html

bm_cricket · Post by **bm_cricket** » Thu Jul 23, 2009 8:37 am

You people are great! I've been planning to build my first dome in the next few weeks. I've been reading up on other people's methods, tips and... mistakes. I think I'm looking for something in the 12' to 15' diameter range. I think I want to try building a 3v dome. What tips do you have for that size? I don't plan to hang anything from it and I don't plan to climb on it but it would be nice if it could last a few years. I will most likely use it as a green house for most of the year too (with clear plastic). What size pipe should I use? What about treatment so it doesn't rust quite so much?

I do not have a hydrolic press but after looking at the Vogel Tool & Die options I'm pretty tempted... Has anyone actually used their dies? Do you think the excel spread sheet of smart ways to cut 10' pieces could make it my way? ;-)