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Monday started bright and breezy but soon turned to heavy showers. I had just fixed a 2x4 pier brace up under the floor to the east when I had to quickly gather my tools and take shelter. The 7" x ½" coach screws which I bought early on finally found a use. Drill perpendicular to a double-sloping 4x4 must be a learned skill. Despite marking the starting point carefully it is difficult to keep the hole perfectly square to the post.
An interior view looking north and upwards.
Well, that was disappointing. I bolted two, 2x4 braces just below floor level and found it made the pier post vibrations worse! There was a distinct rattle every time I thumped any of the four posts. The added mass of the braces may well have been responsible. I should really have used F-clamps to check the effect of bracing before I bolted them in place.
So then I tried clamping lengths of timber in various positions up and down the pyramid. Nothing really helped. A long board of plywood low down across the eastern legs might have increased the frequency. Though the effect was hardly noticeable and could have been entirely subjective. I just hope I don't have to clad the entire pier in plywood! Apart from the expense, getting all the adjoining edges straight and to exact size would be quite a struggle. Overall cladding would also steal all of the useful space on the ground floor.
The vibrations from a thump with the side of my fist is definitely cleaner and shorter lived without bracing. The plywood cladding at the top was a noticeable improvement. It also provided secure location against sliding movement between the pier posts. I can lean into the top of the pier without obvious movement. Except to the building around me. Which will move about an inch, north-south or vice versa.
My attempts to find a Danish dealer for one of the "Eco" mineral powder, wood protection products has failed. I tried the usual product names and a few [Danish] terms likely to throw up a response to a Gurgle but without success. It looks as if I'll have to order a pack from the UK. One eBay dealer wanted the same price as the product for postage for a few grams of dry powder in a paper bag style of packaging.
I used my laser device to properly measure the pier at 3.77 meters tall inside. [Off the ladder ground slabs.] Add another 10cm for the thickness of the top blocks and that becomes 3.87m. That's 12' 8.3" in Old Money!
Now I have no choice but to put a telescope and the heavy mounting on top of the present pier to see if it shakes at high powers. [Or even at low powers.] I am hoping that it will remain stable provided I don't hit the pier. Electric focusing might be useful. There is absolutely no fear of it toppling but any unwanted movement is highly undesirable. Who knows how it will behave with a couple of hundred pounds stuck on top. It might shake for weeks!
I've spent years taking handheld astro-snaps at the eyepiece thanks to "rock solid" welded steel piers. I could thump the 6" f/8 refractor OTA and the image hardly vibrated. That incredible level of stability might be harder to obtain with a 12' 8" tall pier, a heavy mounting and the "long" 7" f/12 refractor!
Tuesday: Mixed cloud and sunshine but remaining dry so far. Made a start on measuring, marking and cutting the flooring for the observatory area itself. The veranda will have to wait for wood treatment to the joists. It would help if the boards weren't bowed laterally. I may have to plane the edge of one plank to make it sit closer to the next. I've left it with three long F-clamps pulling it straight while I have lunch. I couldn't flip it or reverse it after cutting notches for the pier legs to clear.
Click on any image for an enlargement.
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2 comments:
Really enjoying your blog and seeing the observatory improve every day. It will be an amazing structure even if you do suffer a little vibration.A couple of thoughts cross my mind if you are interested. I work everyday with wood and restore antique furniture for a living, also love to restore anything from old telescope mounts to old motorbikes!. One thing I have learned is that all wood will always continue to "move"even 200 year old timber will shrink and expand as the moisture content varies from day to day. Wood seems to absorb moisture more slowly than it will give it up, but the only way to minimize this is to constantly monitor and control the relative humidity. Wood will readily shrink and expand across the grain but also along the length but to a much lesser degree. My concern is that if you polar align your scope, that given the huge wooden tripod that supports it, you will have problems as the wood moves with the humidity.Just a thought and hope that I am wrong.
On your latest problem drilling holes perpendicular to the beams I had a friend from Australia who invented a device that you could attach to an electric hand held drill that in effect turned it into a drill press. Such a simple thing but not only did it keep the drill at right angles but also via a lever gave you a huge mechanical advantage just like a drill press where little effort is required to drill a hole. It worked by having an adjustable extended arm that extended to hook around the back of the timber you are drilling and would work on window frames joists etc with a capacity of over 12 inches.Rather surprisingly after mocking one up and investing much time and money in it all of the manufacturers including Black and Decker turned him down. Maybe they prefer you to break drill bits which often happens with the smaller hand held drills. Perhaps if you have a lot of holes to drill you could at least make a jig out of ply that would clamp to the joist and keep everything square. I sometimes do this when drilling into the edge of a table leaf to a depth of perhaps 8 inches and the leaf is less than an inch thick Good luck with the building and really admire your drive and enthusiasm for this project.
Best wishes
John Saunderson
Living in England
Hello John and many thanks for your fascinating comment.
We seem to have a broad range of similar interests.
Agreed on most of your points. Precision, wooden pendulum rods have similar problems. They were usually waxed or varnished to slow variations in humidity. Otherwise wood would make an excellent material with a very low coefficient of expansion. Heads you win..
I believe I've seen clamp-on rings to go around an electric drill collar just behind the chuck. The expanded ring, with a suitable stand-off, provided simple guidance to keep the drill perpendicular to the surface on which it rests. These days they don't bother with collars as add-on tool interfaces and every drill is "styled" independently.
I have just ordered some "Eco mineral powder" to treat my timber against rot and fungus. It is simply added to water and painted on. Do you have any experience with these products? Reviews seem favourable and I'm hoping for an instant "weathered" look without toxins. I used potassium permanganate to 'age' pine on new backboards for old clock cases. I'm hoping for a similar grey-brown appearance like driftwood but without the years of waiting for it to occur naturally.
Regards
Chris
In exile from Gravely Blighted.
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