Friday, December 08, 2006

Hoisting the Beams

After eating a big breakfast, we started moving the beams down to the tree site. It took three trips with the tractor, one trip for each 16 foot beam, and one trip for the two cross beams.

In order to get the 16 foot beams up into the tree, we installed a lag bolt 3 or 4 feet above where we expected the permanent eyebolts would be screwed into the tree. We attached a pulley to each of these upper lag bolts, and then tied a rope to each end of the beam.

The plan was to pull up one end of the beam, tie it off, then pull up the other end. Luckily my brother-in-law Jason showed up, giving us a much needed extra set of hands. This was definitely a three person job, and we could have used a fourth.

One of us did most of the pulling, one guided the beam past the scaffolding and other obstacles, and the third took up the slack in the rope, wrapping it around another tree so that rope couldn't accidentally slip out.

After getting each end of a beam up to an appropriate height, Dad climbed either the scaffolding or a ladder to tie that end of the beam off. We used a lot of rope in the process, and often had two or three methods of holding each end of the beam up.

This was a lot of work, luckily our support crew showed up with some good mexican food that gave us a boost.

After getting the main beams up, we temporarily bolted some 14 foot 2" X 8"s across the trunks, so that we could rest the beams on them. We did this so we could later move the main beams around a bit to bolt the platform together. It was at this point that we realized just how much a tree moves around in the wind. I could understand how a statically bolted multi-trunk structure could tear itself apart relatively quickly.

We were running out of daylight, so we made sure we had everything roped off well, and quit for the day. We hoped that the tempoary sub-frame would survive the night. If it didn't, nothing would fall, but it might mean a lot of re-work for us in the morning.

It was another successful day, and it was starting to look like we were actually building something up in the tree.

Sunday, December 03, 2006

Beam Building

The next step was to start building the 16 foot beams. We ripped 4 strips of plywood to sandwhich with the 2" X 10"'s. We debated on whether the seam in the plywood should be in the center of the beam, or out toward the end. We decided it was safer in the middle, since otherwise it'd end up where the suspension points where, which already was going to be a weak point. We intentionally undersized it a bit, we didn't want it to form a ridge on the beam that would make laying the floor difficult.

We then clamped the four pieces together, and ran carriage bolts through the beam to hold it all together. Next, we used the outer plate of the suspension brackets as a template to drill holes through the beam. We wanted to get as much done on the ground, in the shop, as possible. Trying to do this kind of work up in the tree sounded nearly impossible.

It took a solid day of work to build up the two beams this way, and get the hardware mounted to them properly. We estimated that each beam was well in excess of 200 pounds, possibly as high as 300 pounds with all the hardware on them.

It took a few more hours to build the two connecting beams. We used two 2" X 10"s again, but this time without the plywood in between. In hindsight, I wish we had put the plywood in there due to the stresses on these beams caused by the suspension points.

We then bolted the whole thing together, and checked for squareness. The angle brackets appeared to keep everything square, it measured square on first try.

We labeled all the sides so that we could match everything up correctly when we were in the tree. We disassembled the platform, and tried to mentally prepare ourselves for the next big task, actually getting it up in the tree!

Saturday, November 25, 2006

Final Design and Lumber Trip

There were still a few things to figure out for the platform. The heart of the platform is two 16' beams. We tossed around all kinds of ideas: Rough sawn lumber, reclaimed beams from old buildings, built up beams, engineered beams, etc.

We knew the structure would sit out in the elements over the winter, so it had to fair well in wet weather, that ruled out a few options. We didn't want it to warp as the timber dried, that threw out the rough sawn beam idea.

After some advice from our friend Tommy who had a lot more experience doing this kind of thing then we did, we went with the built up beam idea. We'd use two 2" X 10" X 16', with a .75" layer of plywood sandwiched in between for each beam. We figured the plywood would add support to any weak points in the beam. Each beam would be suspended from two points, with about a 10' span between suspension points.

After changing our minds several times over a few months, we settled on a in-frame floor joist system. Originally Dad thought that the joists should sit on the frame, but he came around to hanging the joists inside the frame. It helped solve a few problems: the plywood floor on top of the joists would help keep the frame square removing the need for cross braces. It saved us from buying two more 16' pieces of lumber to use as joist caps. We also didn't have to worry about hurricane clips, or other methods of ensuring that the joists would stay on top of the beams.

With these decisions made, we updated the drawing, and calculated how much lumber we'd need. We decided to go with preassure treated lumber, since it would be exposed to the elements, at least for several months.

We rolled down to the local lumber yard, and spent a good amount of time picking out the straightest and strongest looking lumber. We went through every piece of lumber that was apporpriately sized.

I was amazed at how heavy treated lumber is. I was also surprised by how expensive it is. The lumber plus a bit of miscellaneous hardware totaled about $500. Ouch. Hopefully this painful trend won't continue.

Thursday, November 23, 2006

Build Trip!

In early October, I headed back to Indiana to hopefully build the platform. There were still a few design decisions to be made, but I had a pretty good idea of what the end product would be. I was hoping that the weather would cooperate and that nobody would get hurt.

My Dad and I got started setting up a base camp near the tree. Luckily it was possible to drive within 15' of the tree, which made it easy to haul supplies to the site. We cleared out some of the underbrush near the tree so that we'd have a nice clean work area.

We set up about 18' of scaffolding along one side of the tree. We roped it off to one of the trunks so that there wasn't much chance of it tipping over. At first it seemed impossibly high near the top of the scaffolding, but after a few trips up and down I started to get use to it.

All 300 pounds of hardware showed up successfully. Making sure everything was there by the time I showed up required more planning than I expected. I was really nervous that I'd show up and some critical shipment wouldn't be there, and I'd lose a few days waiting for it. I was happy to see that all the heavy packages had made it OK.

Tuesday, November 14, 2006

Designing the Platform

Next, I needed to design a sturdy platform that would both fit in the allocated space, and be a good sturdy foundation for the rest of the treehouse.

After drawing up the layout of the tree trunks on the computer, it looked like a 8' X 16' platform would fit nicely between the trunks. I originally had thought of using all 5 trunks, and perhaps making a pentagram shaped floor, but the nice square 8' X 16' platform looked larger, and much simpler to make.

The next trick was determining how to attach it to the tree. Since we'd be building in a multi-trunk tree, I had to take into account the independent movement of each trunk. I tried coming up with all kinds of sliding brackets, similar to what other people have done. The result was a lot of complicated brackets that looked expensive to make. Plus, I wasn't really sure they'd work in all possible scenarios.

One of my friends suggested suspending the entire thing via chain. The more I thought about this, the better it sounded. It would definitely solve the trunk movement problem, and I liked the idea of a suspended platform that would perhaps have more movement than a fixed point platform.

I spent a bunch of time at reading up on hardware that looked appropriate. I eventually arrived at using a combination of eyebolts, shackles, turnbuckles, and chain. I went with the largest eyebolts I could find (1" in diameter), figuring that they were going to be the weak point of the system. The eyebolts pictured below are rated at 10,000 pounds if pulled along the line of the bolt. Since I'd be pulling on them perpendicular to the bolt, they'd support significantly less weight before failing.

I didn't want to just run the eyebolts through the frame of the treehouse. I was afraid that they'd deform the wood, with all the eventual weight that'd be resting on the frame. Instead, I drew up a bunch of various right angle brackets and plates that would help distribute the load over a larger portion of the beams. After showing the various designs to my dad and other friends, I settled on some simple 1/2" thick right angle pieces, along with some 3/16" plates.

With these decisions in place, I updated the CAD drawing, and ordered a bunch of hardware. I hoped we wouldn't change too many aspects of the design once we started building, mainly because of the investment in the hardware.

Wednesday, October 18, 2006

Scouting the tree

Several months ago I read an interesting one page article in the back of Make Magazine about a guy who lived in a treehouse for 3 years in the 1970s. I hadn't thought about treehouses since I was a kid, but the article struck some kind of chord in me, and I started thinking about building one.

In the spring of 2006 I headed to the family farm in southern Indiana to see if I could find a suitable tree. I hiked around with my folks for a few days, and we eventually settled on a Sycamore tree that had grown out of an old stump. The tree had sprouted 5 trunks, and it looked like we could fit a good sized treehouse between them.

I wanted to put the tree up a good distance off the ground. After climbing around in trees all weekend I realized being up high in a tree was a bit more frightening than I expected. 16 feet off the ground seemed like a reasonable distance.

My dad and I measured the circumference of each trunk, and also measured the distance from each trunk to every other trunk. This allowed me to create a scale drawing of the tree at sixteen feet. I headed back to Colorado for the summer with enough information to start designing the treehouse.