Today I assembled the ribs and a quick waterproof undercoat, pic attached.
Is it dodgy?, of course it is. You wouldn't want to get a ruler near it, you dont need that kind of negativity in your life.
That's the spirit...you may have issues with your first one but after a few it becomes easier
I am in awe.
So many times I have close to having a go which given the initial planning gives me some idea of the undertaking your have set upon.
And it is good creating an audience as hopefully our prescence will encourage you to put the time in a provide photos and progress reports.
Why shouldn't fibre glass be water proof? I think they sometimes use it for boat hulls.
Thanks for the encouragement guys.
Alex. Yes, the initial planning is frightening, but once you get started, winging on the fly reveals how much easier it can be.
It looks like small progress today but significant. After overthinking for hours I decided to go for 0.55 mm gal sheet covering instead of 3mm ply. On this test segment, It turns out its easier to work with, you can bend more. I nicked the edges folded them in level with the frame and screwed on. the edges look ugly, but ill cover the segment joins with wide flashing tape. Thick, sticky, waterproof and flexible, it will look fine and hide the nicks and screw heads.
Who ever dreamed up "measure twice cut once" obviously never built a dome. What if every-single-time you measure its different!!!. Spend all day measuring?, so silly.
Sometimes you have to use common sense, eyeball it and just get it done.
No measuring at all with the segment covers. Push gal against ribs, run round the inside against the ribs with a texta and start snipping, easier than I thought it would be, perfect!.
More al segment covers fitted today. I switched to a cheap Ozito jigsaw instead of tedious manual snipping. So fast, so loud (thin al is an efficient sound transmission device). What struck me was how stiff the whole structure became when the curved al was screwed on. It almost doesn't matter how stiff the ribs were.
Looking good! likely to late but as well as the tape over the joints I would look at one of the " non setting mastics " to seal between the sheets.
They are better than silicone as they skin where exposed to the air but other wise stay " wet " from memory they are about the same price as silicones. I brought a box from a local caravan repairer and they were cheaper than bunnings silicone.
And without meaning to rain on you, do you plan on being in the dome with your scope or will it be a remote setup?? I realised you said 1.5m in diameter when my brain was thinking 1.5m radius!🤦*♂️
Looking good! likely to late but as well as the tape over the joints I would look at one of the " non setting mastics " to seal between the sheets.
They are better than silicone as they skin where exposed to the air but other wise stay " wet " from memory they are about the same price as silicones. I brought a box from a local caravan repairer and they were cheaper than bunnings silicone.
And without meaning to rain on you, do you plan on being in the dome with your scope or will it be a remote setup?? I realised you said 1.5m in diameter when my brain was thinking 1.5m radius!��*♂️
Ed
I left a bit of a gap between the sheets, so yes ill look into mastic also, i was wondering what i would do with the gap, thanks for that!. Better than the middle of the tape hovering over the gap or silicone. I dont intend to be in the dome whilst imaging, although im pretty sure theres space enough to get in it if i have to, its only a small refractor.
Ed
I think its one of those things you only built once, and do a ROR next time, its not a trivial task.
The dome will sit on a 1m odd high round pedestal (with an access hatch).
The driving, well thats a head spin. The last resort will be a 3D printed circular rack and pinion in sections but thats a monster print job, so im thinking of other rack like things like timing belt or chain stuck to the side, even bolts every 20cm or so as "teeth".
The latest learned thing (bit obvious really) is the waste in cut offs, some 30%. Round is a bietch.
Angle aluminum is very useful in building an obs, wheels can run on it, the angle part can be used to guide with more wheels say on a ROR. Its thin and strong.
But its straight, no use on a dome. I need to make a curved rolling slot cover with extra wheels also for guiding and some way to stop it falling off. Im thinking more tedious chunky circular bits in plywood from a large sheet.
BUT NO, you can bend angle aluminum into a circle without some fancy bending machine, I kid you not!. (I can hear mechanical experts saying duh, im not a mechanical expert).
Upon googling, turns out you can turn angle aluminum into butter and bend anywhich way by annealing it!.
Looses some strength but I dont care. to anneal, you heat up to a specific temp and let it cool naturally. How to know the temp?. its nuts, do some squiggly lines with a sharpy (a sort of texta, bunnings have them) and when you heat the al with a blow torch you know the temp is right when the sharpy lines disappear.
So off to bunnings, get a bunch of angle al, a blow torch, sharpys and start learning. The test went very very well!.
all the segment covers on now.
As a complete dome, it won't go through my workshop door, a real pain working outside (it can get windy cold in Torquay), so I separated the 2 halves and will work on rails etc separately in the workshop. What a difference!. Access to the slot is now soo easy and convenient. once rails are completed (and pretty much everything else), ill just screw the 2 halves together and install the fixed slot covers.
Now that I know how to bend angle al, no chunky ply for the rolling slot cover, hopefully, ittl be sleek and slim built with al and gal only.
Thanks Adam.
The Ryobi is the best cheapest at bunnings IMO at $269 and suits my occasional use, cant be bothered spending more on this. Drills smooth and true and has good reviews. Although I like Ozito cordless tools, their drill press is rubbish (well, its $129!), wobbles all over the place, bad reviews. These 2 are the cheapest by far, not a big choice at bunnings.
you see, bunnings is 5 mins down the road, i live in bunnings, anything else is far away, im in regional victoria.
Thanks Marc. Well, i didnt get away with it entirely. Had to get a ruler near it again and make some adjustments so the cover slot will roll over the hoop. It has to be the same diameter right round, damb it.
Quite a feat to match curved beams like that and get away with it. .
Actually, that part wasn't so hard. I Drew the dome in fusion360 (free version, any CAD software will do, like sketch up), captured jpegs of different views along with the background grid to give scale, printed them at A3 size, measured each item with a ruler, multiplied by the grid scale and got the height of each rib. The diameter curve of each rib is the same so I only needed the height and angle of the end cut for each rib. string and pencil on the ply sheet for diameter and cut to height/end angle. Printing scale is almost random, so the printed background grid made that irrelevant. If anyone wants the original captures, your wellcome, can be scaled to any size with the aid of the background grid on each pic.
After days of considering a 100 ways to drive the dome, ive decided to 3d print a circular rack afterall, because i know it will work. Custom made racks are crazy expensive.. To design this I thought would be a nightmare, but no, to my surprise a free plug in for fusion360 called Helical gear plus (also does straight) is super easy. Enter diameter, number of teeth, teeth pitch and your done. Ill split it up into printable segments and add mounting holes. The gear to match is easy. The attached pic shows a list of steps that were just me just mucking around with parameters. I have bought and tested a bunch of 12v geared motors off ebay at $24ea that albiet are small, but strong and robust (al case and brass gears), and given the price ill use 2 or 4 or them (or more) round the dome in parrellel. Less stress on the ABS rack that way too.
Well done, Fred.
