Tuesday, August 21, 2012

Geodesic Dome, or the Burning Man house.

My best friend and I are going to the Burning Man festival this year.

With the summer spent in the North with the kids, I haven't had much time to think about and plan for this week long festival in the desert, and Nicholas has been equally preoccupied with his work/life/pie business.  

Last week, after the unpacking and settling in, the pending adventure started sinking in.  

We decided to do something a little more fun than sleep in a tent for a week, and I got cracking on a geodesic dome.

I went with a 2V design, one of the more basic options, with only two different component lengths, resulting in 6 pentagons that make up the half-sphere.

35 pieces of 10 ft. 3/4 inch EMT conduit.  Available anywhere, around $4 a stick, total cost was a hair under $150.  You can play with the measurements on a 2V dome to get any radius you want, but to minimize wasted material, I went with the proportions that would allow me to cut the 10 ft pieces once and have my two different lengths.  That ratio is roughly 4.7 ft and 5.3 ft.

Done in the yard with a 4.5 inch angle grinder with a metal cut off wheel.  Used one wheel ($2) and took maybe 20 minutes to mark and cut them all.  

The next step is flattening the ends of each piece, where the bolts will go through up to six pieces at a junction.  Some folks do this by hand with a hammer, which for 65 pieces, on both ends, is a ton of hammer-time.  (I hope that's not the only time in my life I get a legitimate opportunity to write that.)  Others track down a hydraulic pipe press.  I am lucky enough to have a friend in town with a sheet-metal shop, and borrowed his big press for an hour.  It did an amazing job.

Notice the big press put an angle on the flattened ends.  These ends need to be angled, but with specific angles for each size, and after the drilling step, so I had to straighten these pieces before moving on.

These six moderate bundles of pipes, and a bag of nuts and bolts, is the whole dome.  Nice and compact for travel.

I straightened the angled ends with a simple vise set to the width of the squished end, stuck each piece in and bent it straight.  Maybe 15 minutes to do them all.

Drilling.  The pieces will be bolted together with 5/16 bolts, so the pieces needed to be drilled on both ends with  a 3/8 drill bit to make getting the bolts through a none-issue during assembly.  This could have been a lot easier if I had taken these to my shop and used a jig on the drill press, but to allow me to work on this during the kids' nap time, I went a less organized route.  Simple wooden block with a 3/4 in mark back from one end, I lined each piece up on that block and drilled through with the cordless drill.  (If this was being done without a drill press, I would recommend a corded drill to anyone working with an 18 volt or smaller cordless drill.  Or go out and buy one of these new 20 volt lithium deals, they're amazing.)

This was the step for the first hole in each piece.  It takes a good drill bit to cut through the double-walled ends of 65 pieces; I went through three new ones at a cost of about $7 per bit.

The second hole in each piece needs to be exactly the same distance from the first on all pieces.  Again, a jig on a drill press would be easiest, but working in the yard, I made a simple jig with a screw at the bottom of this post, which the first hole could go over, and a line at the exact distance for the second hole at the top, with a bracing screw.  This also put the drill at a comfortable height to lean into it and punch through more easily.

Total time to drill each piece twice, around 2 hours.

The last step was re-angling the ends of the pieces, 18 degree angles on the ends of the longer pieces, 16 degree angles on the shorter.  Same deal with the vise, a stop block at the appropriate angle, and 15 minutes to put the angle on each piece. (This doesn't have to be super-exact; these angles will be finalized when the whole thing is loosely assembled, and all the bolts are tightened.)

Nuts and bolts:  Each junction needs a bolt, two washers, and a nut.  The bolts need to be 2 inches long for the junctions where six pieces come together, and I suppose you could use shorter bolts for other junctions, but keeping track of different sizes during assembly would be a nuisance, so I went with the single size.  For this reason the bolts need to be threaded all the way up the shaft, which is surprisingly difficult to find in your average hardware store.  Most bolts are threaded for the last (first?) inch only.  I ended up ordering these online, nuts bolts and washers, for $25.01. (Can you guess what the minimum order for free shipping was?)  This gave me all the bolts/nuts/washers I will need for this, and a few other projects.

Assembly:  I suppose this can be done in many different ways.  I decided to assemble the pentagons first, and then fit those 6 sections together.  This was not the easiest thing to do by myself, and on my pretty wood floor in my office, but I still think it is the quickest way to go about doing this, and will be easier on sand.

The first pentagon, ie. the roof.

Five more.

Attaching a pentagon to each point of the top pentagon, and connecting them around the sides to each other.  Our friend and tenant Polly came over from her office and lent a hand.

Using this method of assembly, the thing has no strength or shape of it's own until the final pentagon is tied in.  It makes for a wobbly, aggravating pain in the butt. A big part of this has to do with how loosely the pentagons were assembled; I barely finger-tightened the junctions of the pentagons as many of them need to be unthreaded when they are being connected during the larger assembly.

However, once all the pipes are connected, the thing is surprisingly strong.

Even more so once you go back and tighten all the junctions with a ratchet.  I can easily hang and swing from the top of this, and have no worries about us stringing hammocks from this for sleeping.

I was tickled.  I still need to figure out the covering for it, I'm thinking overlapping tarps given the time constraints, but it didn't stop me from dragging friends from their lunches at the BTC to come upstairs and look.  One of those friends took this picture.

After the covering is figured out, it's disassemble and pack it into the truck for the drive out to Nevada.  When I get back, I'm thinking it might make a neat greenhouse.  Or with some modification, a pig pen?


Anonymous said...

well... that's cool!

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