Topic: Any carpenters here? Building an Octagonal "Glassebo"

[dupreezd]

@SLOweather, good job so far from a fellow woodworker.
If you are going to put your sill plate on concrete, use this between the wood and concrete, this will prevent the wood from wicking up moisture from the concrete and prematurely rot out.

https://www.homedepot.com/p/Owens-Corning-FoamSealR-5-1-2-in-x-50-ft-Multi-Use-Ridged-Sill-Plate-Gasket-2FS/202080947

[SLOweather]

Thanks dupreezd. I just started thinking about the concrete foundation this week, and wondering how to flash it. Still have to figure out making an octagonal form, and the steel, and the J bolts...  Luckily, there's no "frost line" here, so I don't have to dig too deep.

[SLOweather]

I will admit to a little diversion of thought for about a month recently regarding the design of the gazebo

Back when I was in early junior high, my dad and I built a polehouse. None of the trees on our property back in Moline were suitable for a treehouse, so Dad got 4 used utility poles from the local electric company to build it on. It also acted as a shade over the patio. (I have NO idea how the 2 of us managed to set the first post by ourselves.)



I was using a ladder and then a chain ladder to get up into it. The chain ladder was made of old snow chains with EMT pieces slipped over the cross chains for rungs.

My grandfather (Dad's father in law) decided that we needed a better, safer access, and designed and made the spiral staircase you see in the picture.



It's all made of individual pieces of 2x lumber except for the top piece of each riser which is 1x to get the rise correct and fit the stairs into the existing vertical space. He brought all of the pieces up in the trunk of his car from Missouri, along with a scale model to show how it went together. All of it is strung together on a half inch steel pipe up the center, and the treads and riser pieces through bolted at the outside. Then we added EMT flattened, bent and drilled at each end to form a cage around it. One end of each pipe was bolted under a riser, and the top bolted to the underside of the floor.

Anyway, I decided I wanted to recreate that staircase and was looking for a reason to do so. The first thing that came to mind was to make the gazebo 2 stories and run the spiral staircase up the middle. I spent a lot of time thinking about it, and figuring out how to do 14 or 16 foot posts instead of 8 footers, and how to do timber frame joints for the second floor. I was even going to cantilever a deck out from the top floor.

Then I started moving the existing materials around and came to my senses. I can barely handle an 8 foot post by myself. Doubling the length of the 8 of them seemed like a sure way to hurt myself, so I abandoned the 2 story idea.

But I still want to do that staircase sometime...

[dupreezd]

Instead of casting J bolts into your foundation, it might be easier to use this method and use concrete epoxy adhesive. No need to transfer measurements and have bolts and holes that does not line up 

Pour your foundation with out the J bolts.  Pre-drill your sill plate where you want the anchors to be. After the concrete cured, assemble the sill plate over the foundation and run a masonry bit through the holes into the concrete to mark the location of the holes. Remove the sill plate and finish drilling the holes, fill with epoxy and insert the anchor bolts.

Here is a nice video explaining the steps.
https://www.quikrete.com/athome/video-anchoring-epoxy.asp

[SLOweather]

That's another good idea. I didn't want to use any kind of expansion anchor due to potential cracking of the relatively narrow width of the foundation, but drill and adhesive should work fine.

[SLOweather]

More progress. Yesterday I marked the top mortises and chiseled out an eighth of an inch or so. Then I temporarily screwed each top beam miter joint together and drilled them out using the started pocket as a guide. I used my Rube Goldbergian setup of lowering the drill press table and putting the drill press over the workbench, and then plumbing and leveling everything.


Today, I chiseled mortises and sized tenons and got 3 top beams up to finally see what it's really going to look like..




So this shows some of the constant thinking and adjusting that I do on this project.

The sill beams are "shingled" in layout. That is, each beam's joints overlap the one on the left, and is overlapped by the one on the right. This was because I cut the laps on the radial arm saw, and it wouldn't cut left end laps on a 6x6 due to the design of the machine. This isn't a big deal because the base is assembled first and then the joints are pinned by the post tenons.

OTOH, the top beams are cut with either 2 top laps or 2 bottom laps. Originally, I was going to shingle them like the base, but realized that they would have to go on skewed because of the shingling (which, if the joints were tight, wouldn't work), or I would have to assemble the octagon on the ground and try to lift it into place in one piece.

Luckily, I managed to configure the radial arm saw to do left hand laps with a quarter inch to spare.

And, when assembling the top, I have to install one bottom lap beam, skip a bay, install another bottom, and then join them with a top.

[SLOweather]

Dragging this back to weather...

I have just one more top beam to mortise and the timber frame is essentially done. So, I think about the next steps. The foundation, the window sills with 8" tall vents under them, the cupola on the top that vents out the center...

Hmm... what meteorological research device has a cylindrical shape, that kind of venting, and a heat source (in my case, the sun).

Am I making my own tornado chamber???



That would be kinda cool...

[SLOweather]

Woo hoo! I just got all 8 top beams in place. Now that I'm getting pretty good at 2" square mortises, it's nice to be done with them.





Now, I think it's time to take a lot of measurements, and study it, to make sure it's all the same diameter, level, the posts are plumb, and the openings the same size...

[Old Tele man]

Reminds me of that WWII Nazi "henge" in Poland!