Black Oak Observatory Construction
Welcome to a gallery narrating my astronomical observatory construction. Entries will be added in chronological sequence. Click on photos for a larger view. Schematic plans and detail drawings are available here.
foundation framing finish
Bob arrived with the 4x8 beams, 2x8 joists, tongue & groove plywood and a 6x6 post needed to frame the floor. We both carried the 14' beams down the hill and I carried down the joist lumber while Bob set up the transit and inspected the caissons.
We used the transit to set the uphill beam level, then measured the downhill beam elevation above the anchor hardware. Bob cut posts to match, we set the beam on the posts and measured again. After adjusting the post heights to achieve level with the uphill beam, we anchored the posts to the caissons and the beam to the posts.
Bob cut the joists to length and I helped to affix the anchor hardware and install the joists between the beams. Along the way we found the south beam had a bit more curve to it than expected, which required some attention with a sledge hammer.
We quit around 2:30pm, talked about a few job issues and planning steps, admired the work from the residence deck, and unloaded the plywood from Bob's truck. A productive and exhausting day.
Bob arrived around 10am with some additional framing supplies, a nail gun and redwood lumber for the observatory entrance landing.
I asked him up to the garage where we examined the base configuration of the Losmandy G11 and Meade LX200 mounts, and took measurements for the adapter plates we will have fabricated for the steel telescope piers.
I called Meade customer service to get the attachment hole configuration for their Super Wedge, in case I decide to add that later, and was told that it was "proprietary information".
WTF?? Meade is possibly the stupidest corporation on the planet ...
I brought down the redwood, we brought down the subfloor plywood, and we finished up the joists. I made a run to Sebastopol Hardware for more tico nails and hangers, and a few gopher traps.
Laying the plywood took longer than I expected; although the beams and joists were perfectly square, applying the adhesive gloop and fitting the tongues and grooves, chalking the joist lines was tedious work. There were caisson holes to measure and cut, and the nail gun jammed halfway through the work. It took Bob a lot of effort to get out the disfigured nail. I used the time to take down the batter boards and clean up the scrap wood around the site.
We quit around 3pm, hauled tools and the compressor up to Bob's truck. I paid him and we talked about ordering the steel piers, having a trash guy come by to clean up the scrap lumber and trash, and planning to start again when I get back from RTMC on May 31.
As the sun went down Jan and I spent some time looking at the work. The floor seems larger than I expected, even taking into account the 2x6 framed walls. It's going to be a very comfortable workspace.
My weeklong excursion to Big Bear was a mixed bag. The presentations at the Society for Astronomical Sciences 2011 symposium were uneven and vapid. The presentations by Tom Krajci in Tuesday's Automated Observatory Workshop were informed and very helpful, and the astroimaging of galactic streams described by Jay GaBany was fascinating.
The Riverside Telescope Makers Conference was more rewarding but also ultimately disappointing. Friday night I met Phil Sullivan, also down from Sonoma County, and we had an enjoyable evening observing Saturn and a few other skymarks through a variety of telescopes. I examined M 51 through a 26" reflector and Saturn through an 8" Clark refractor from the 1850's. We had an especially rewarding encounter with a young man and the 18" /6 Dobsonian reflector he had built himself: the optics were superb and the views of Saturn, M 5 and M 51 were memorable. The YMCA camp venue was scattered with campers, trailers and all types of telescope rigs, along with a wacky assortment of balding, bearded older white males, a few of them struggling far into the night with their equipment. (We never had a chance to check out a TMB refractor because the owner could not get his Losmandy G11 mount to operate. Turned out he had crossed his servo motor connections to the computer controls.) Unfortunately there was a continuous and occasionally robust wind that produced poor seeing and dusty conditions all night. We quit around 11:30 pm, usually when observing activity is at its peak.
Saturday I arrived early to check out the swap meets and vendor displays. The swap meet ranged from professional used equipment dealers with a dozen tables of displays to a guy with a card table and two eyepieces to sell. Retailers OPT and Woodland Hills were there, with manufacturers such as Meade, HoTech, PlaneWave and Explore Scientific. Overall, a vast and raggedy garage sale. I bought a few long focal length eyepieces from Gary Russell, and got a spectacular view of the sun through a 100mm Lunt solar telescope.
Sunday was the low point. A brutally strong wind blew across the region all Sunday morning, ripping screens off the windows of the Northwoods Lodge. I arrived early at RTMC to attend an astroimaging workshop, and found the grounds in total disarray. Campsites and vendor tents had been torn down and scattered by the wind; people were packing up and leaving in droves. (Phil had left Saturday afternoon.) The astroimaging workshop by Craig Stark was plodding; he took the entire morning to explain the simple pixel/f-ratio/seeing dependency.
Rather than gut it out and make the long drive home in the dark, I decided to bail after lunch. I followed the route suggested by Phil in a farewell email: down the mountain on Hwy 18 north, up 247 to Barstow, across Hwy 58 via Mojave and Tehachapi to Bakersfield, up Hwy 99 and across Hwy 47 to I 5. It was a great drive to make in a Porsche, with spectacular landscapes and brilliant cloudy skies. I was home by 8:30 average speed 67 mph, including a rest and refuel stop.
You know the vacation was disappointing when the best part about it was the drive home.
Then came a week of rainy weather. Supposedly this weekend is the last of it; the winter jet stream is finally breaking up and will reconnect along its summer route. In the meantime I reviewed the studio measurements to prepare a lumber checklist, and pursued the fabrication of the steel telescope piers, which has turned out to be a peculiarly difficult problem. More about that next week.
Bob is still recovering from a bad cold, so we planned a light day. He came by around 9am, just in time to offer advice on a storage box for towels & chemicals my wife is having built to accompany her new outdoor hot tub.
Bob and I drove in his truck to Petaluma, to pick up a pick up steel tube pier at Maselli's, then drop off the pier and plans for fabrication at Reliable Hardware in Santa Rosa. It was a beautiful sunny Sonoma morning and Bob chose some lovely back roads for the journey.
Maselli's is a full inventory hardware and construction supply store fronting an enormous mazeway scrap yard. Bob and I spent a little time marveling over the amazing collection of junk of every type, binned and stacked along wandering passageways. I hailed a yardman who showed us the 13' section of scrap square tube steel that I had reserved for the telescope piers; we deemed it sound and only superficially rusted, and had it loaded on Bob's truck for the trip to Reliable.
Why square tube steel? Software Bisque and Durango Skies use 10" diameter, 1/2" thick circular tube steel in their standard steel piers and indeed a circular telescope pier seems to be the majority preference among amateur astronomers. However the source of tube structural rigidity and strength is not primarily in the wall thickness (beyond the thickness necessary to prevent buckling) but the tube cross sectional dimensions. On that point, the square steel creates a diagonal that is 35% longer than the nominal dimensions, which provides greater strength with less mass. Here are comparative numbers from the Steel Tube Institute of North America's brochure of dimensions and section properties:
| ||weight per foot (pounds)|| ||50.8||47.9|
|wall thickness (inches)||0.47||0.35|
|cross sectional area (in.2)||13.9||13.2|
|moment of inertia||159||202|
|elastic section modulus||31.7||40.4|
|governing radius of gyration||3.38||3.92|
|plastic section modulus||42.3||47.2|
Besides the 6% lighter weight (and lower cost), the flat sides of the square create a larger gap from the base plate edge, allowing the threaded anchor rods to be set farther toward the centers of the concrete caissons. The flat sides of the piers also allow more convenient attachment of cord wrangling tubes or clasps.
That afternoon I finish cut the caisson openings in the subfloor and made two 15" diameter, 1/4" plywood disks necessary to dampen vibration across the base diaphragm between the caisson and steel pier. Fitting these, I discovered that one or two anchor bolts were out of alignment, probably due to deflection by the caisson rebar cage or knockabout concrete pumping. I also found that the bolts were
Around midnight I went out and resighted celestial north. I dropped a plumb line a hex nut tied to orange survey cord from a 9 foot ladder set on the north side of the observatory floor, then sighted through the cord to Polaris with a laser pointer. (The cord fluoresces when struck by the laser, and Kochab was almost directly above Polaris.)
I marked the heel of the laser pointer and the location of the hex nut with a Sharpie; this gave me the line to celestial north. Next morning I strung a cord between the two points, then used two large sheets of drawing paper to make rubbings of the anchor bolt ends. I marked their orientation to the cord, reconstructed the base plate circumference and square pier orientation, and dropped the templates off at Reliable.
Today was lumber delivery day. Bob went to Berry's Sawmill and Lumberyard in Monte Rio and hand selected the framing lumber for the walls and roof. He arrived around 11:30 am, and we spent three hours unloading the lumber from the truck and walking it down to the observatory site.
Midway we stopped for an hour to rehydrate and review plans and construction alternatives, including insulation, painting, and choice of floor covering. I am still undecided between martial arts mats and oak lumber for the flooring.
i cut studs and plates for south wall on the weekend, shopped for painting supplies, paintvand grout. started burying grade beams, bob arrives on Monday with T1-11 panels. begins to frame south wall. gustavo arrives to finish unload, clean site, prime T1-11, cover grade beams. bob goes, i cut studs and plates for second wall.
First wall primed, framed with straps, t1-11 primed, siding installed, ends cut, Phil arrives, wall goes up, second wall framed, lunch, more priming, phil leaves, siding on, end cut, forgot straps, end for the day.
Bob arrived early and was working before I was. By the time I got there he had installed one strap. He cut the doorway and we attempted to lift the wall but it was too heavy. Gustavo arrived, and the second wall went up in a mild breeze. Bob put Gustavo to work fixing the second strap, cleaning up the site. I went inside to calculate the stud cut specifications for the east and west walls, and Bob and I began cutting these as Gustavo laid them out for nailing. I had to go back inside to calculate the length of the top plate, and Bob and I discussed different designs for the rafters and caster plates.
Gustavo nailed the west end wall studs and plates, Bob applied two sheets of T1-11 and trimmed the bottom and top. The third wall went up with levers to get it off the floor and then easily lifted between the two walls. All three were nailed together at the north and west posts. Bob and I admired the work, and Bob and Gustavo left for the day. I set and pulled nails in the siding and examined the obstruction profile on three sides.
That night I took a picture of the moon rising behind the black oak, seen through the unframed east wall opening. This June is an extremely rare month: solar eclipses on the first and last days of the month, at the south and north poles, and a lunar eclipse on the 15th. An auspicious month for observatory construction.
Today was errand day. Bob came by at 9am and we headed to Mead Clark to buy more primer paint, the lumber necessary to finish framing the walls and roof, attachment bolts and hardware for rafters and the roof caster tracks, and the corrugated metal roofing. I ordered a fiberglas exterior door, and we went to Reliable to pick up the galvanized steel tracks. Then promptly back home to greet my wife, just returned from two nights at the San Francisco Opera production of Wagner's "Ring" cycle.
I have yet to secure an electrician to bring power to the observatory, but want to find someone with computer or electronics related experience, so that there is no problem with the 12V power requirements of the telescopes and their computers.
Bob came by at 9am and in short order we had the remaining studs cut for the east wall. I primed the exposed posts while Bob nailed the frame, then we placed and nailed the siding, trimmed edges, and put up the wall. Bob folded over and secured the remaining corner straps, and cut 16" sections of T1-11 to finish the corners on four sides. We unloaded plywood to surface the roof from his truck, and Bob took off for another job.
I have the interior studs and four more sheets of T1-11 to prime, finish strips to stain, an entry landing and a storage cabinet to build, which should occupy my weekend while Jan is at the San Francisco Opera watching the end of the "Ring" cycle.
Next week Bob comes on Tuesday; we hope to get the external roof track beams up, and the caissons leveled with grout, before midweek, when I leave for a family visit.
A week of delay. Bob asked to go sailing on Tuesday, then asked to skip Monday because of an extreme (90°+) heat wave. I consented because I also did not want to work under a scathing sun.
Wednesday Jan and I left for Eureka to visit my parents and celebrate my dad's 90th birthday. We returned Saturday, and had a stalled car to deal with on our way home with groceries.
Sunday I finished priming the interior walls and studs, and stained the exterior cedar trim strips. I decided to postpone building the observatory entrance platform until after the steel piers are installed, which will happen after the roof construction is completed.
Rain is forecast for Tuesday, so we will probably level the telescope caissons on Wednesday or Thursday. The fiberglas entry door is scheduled to be ready before the end of this week. We should have the external beams and roof framing finished by then as well.
A long but productive day. Bob arrived with his laser guided Hitachi saw, and we dollied it down the hill. He nailed up the beam brackets and we went through the pile of beams and posts: measure the post height, cut the post, brace it up on the caisson, cut the beam, set the beam, and so on.
After the last beam was completed and the posts were braced with diagonal 2x6s, we stretched a tarp over the observatory in the chance that the rain forecast for tomorrow might actually happen.
One of the beams turned out to have a troublesome twist and warp, so I asked Bob to pick up a replacement. We resume work on Wednesday.
Rory at Reliable Hardware called with some questions about the fabrication of the steel telescope piers. So work on those has started, and may finish before the 4th of July.
Work the past few days has been difficult. We seated the replacement beam for the east external track, and strung the track surface the entire length of the raised beams. The replacement beam post turned out to be about 5/16" too high. Bob removed the post cap, cut down the post with a skillsaw, and we seated the beam again. This confirmed that the replacement beam was also twisted, so I asked Bob to return the unusable beams and get a third one.
Stringing the track supports also showed that the opposite post was not plumb, so we knocked off the diagonal braces to align it. In the new position, the diagonal braces were too short, so Bob had to also get new pressure treated 2x6's to make new ones, along with the third replacement beam, which was specially cut from a 20' piece.
While Bob was occupied with these repairs I brought down the 30 16" square paving stones for the observatory pathway, one at a time. Bob suggested using the hand cart, but a load of five tiles flattened one tire and bent the axle. I was content with exercise instead.
North track finished, we strung the south track and found that the southeast post was 1/4" too high, so Bob removed the post cap and cut that post down also. After all these adjustments everything looked level and straight, so we final nailed the post caps and beam brackets. In all, it took us four days to get the beams done right.
Today we braved the hot sun. Bob tacked up the exterior trim and I primed all the lumber and plywood for the roof construction. Bob also prepared the sonotube sections to pour the leveling grout on the telescope caissons. We decided it was too hot, and we were too tired, to do that today. After Bob left I primed some of the roofing plywood, but ran out of primer before I could finish.
Work on the steel telescope piers has gone slowly; the welder had a well pump emergency at home, then took two weeks off to get married. I stopped by Reliable Hardware to inspect the work and so far it appears carefully done. Dale had called to say that the tube steel was badly pitted, so I opted to paint it myself rather than have it powder coated, but inspection of the partially completed piers shows the steel is actually in good condition. I'll paint them anyway.
At this point Bob and I are both feeling the effects of cumulative fatigue and heat stress. The 4th of July weekend gives us a welcome few days of rest, and gives me the leisure to enjoy my wife's birthday!
Today we tackled the step that has troubled me the most: construction of the rolling roof.
Over the weekend I laid the rough lumber in place and studied the assembly problem. I realized the framing itself wouldn't be as hard as I anticipated. Sure enough, Bob arrived around 7:30am, we got an early start to beat the forecast noon high temperatures. We discussed all the assembly steps and specific issues that bothered me. Then we got to it: cut the lumber and put it together. We had the rafters in place and blocked, and the plywood on top ready to nail down, by 11am.
The photo below shows a detail of the interior framing. I bought 16 post plates and bent them 90° across the midline to make paired rafter plates. These tacked down quickly. When we were finished, the roof squared up perfectly.
Tomorrow we will chalkline and nail down the plywood roof material, jack the roof up off the rail plates, install the casters, place the angle steel track, set the roof on the track, and roll the roof to align the track before we bolt it down.
After Bob left I went to Willow Wood for lunch, then stopped by Phil's workshop to use his bench vise to bend another 16 plates. These will be the rafter plates when we frame the second half of the roof, probably on Thursday.
Oh joy. We're into the home stretch.
next : finish