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Rusted

Advanced Members
  • Content count

    249
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About Rusted

  • Rank
    Star Forming

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  • Website URL
    http://fullerscopes.blogspot.dk/

Profile Information

  • Gender
    Male
  • Interests
    ATM, imaging, Solar system, photography, blogging, cycling.
  • Location
    Darkest rural Denmark
  1. Rusted

    DIY rotating Nissen Hut or Pulsar 2.7m?

    I checked the weight of the cladding panels at 35kg. The shutters will probably be around 50kg total. I could load the dome to see how that affects rotation. Though I expect it will just be more difficult to get going. The wheels/rollers are massively overrated for these loads.
  2. Rusted

    DIY rotating Nissen Hut or Pulsar 2.7m?

    I hand crank driving a gear set [like a boat winch] or even having a cable wrapped around the dome might work. A counterbalance weight would allow bidirectional rotation simply by reversing the crank rotation. Plenty of room for the weight drop. Now you've got me started on the next building phase and I've not even finished the dome yet.
  3. Rusted

    DIY rotating Nissen Hut or Pulsar 2.7m?

    Thanks & a very good question. The covering is 4mm birch ply. I suppose I could easily weigh that up since the panels are all sitting in the shed ready to go back on. Then there are the shutters and supporting rails. Followed by several layers of paint. I deliberately chose large, free turning, hard plastic wheels with bearings for the support/rotation rollers. Fingers crossed it still rotates just as easily once "fully loaded." I could add more wheels if it would help. Several cranked handles, inboard of the ring and much lower down, for easy reach, will help if I need to put my shoulder into it. It rolls noticeably more freely once it gets going. So inertia is the larger factor over rolling resistance. I'd rather avoid a mechanical or electrical drive system at first because it could easily become a project in itself.
  4. Rusted

    DIY rotating Nissen Hut or Pulsar 2.7m?

    My 3m, 10' dome being rotated by hand Scene 1 take 6:
  5. Rusted

    Help - 24in Mirror Flat?

    A large flat can be tested face up in a water bath [or transparent oil] with a monochromatic light source. The fringes which appear must be perfectly straight. [Give or take the curvature of the fluid surface itself.] An alternative is to set up the flat safely and examine the reflected image of the sky with a mounted telescope. Any deviation from optical flatness will show in the distorted image as astigmatism or change in focus from the direct view. A skilled and productive optician might well have invested the time and expense in a large test flat. Or obtained one for testing his optics. Despite the modern taste for thin mirrors that Zerodur blank is probably really valuable to somebody. Finding that somebody and then getting the blank to them, in one piece, is quite another matter. Alternatively, modern cutting techniques would allow a couple of 24" blanks to be sliced out of it.
  6. Rusted

    Open-Air Pier Mount

    I've kept my vintage mountings out of doors for years. Lightweight woven tarpaulins don't last forever. They and poly bags underneath eventually die from UV-itis. Multiple layers or commercial covers are probably better. I've been tempted by long life, heavyweight tarpaulins but haven't invested. I just keep fitting new woven "leaf collection" bags when they "wear out." A cord around the base of the bag helps keep out the birds and wasps. I had a nest in the fork of my MkIV once so tightened the noose. [No eggs!] No sure about the longevity of cosmetics or complex electronics on modern mountings though. My mountings do "weather" over time despite being covered. Condensation and dew are constantly cycled by soaring temperatures. Watch out for wind though. I've had massive, cast iron piers with flared bases topple over in gales. Fix any pier down to ample concrete!
  7. Rusted

    Teflon bearings for Dobs

    eBay[UK] has excellent Teflon/PTFE dealers with very reasonable prices in "normal" thickness sheet. Save hours of messing about? Otherwise a bandsaw fitted with a fence and/or a sled will slice it into usable circles as Tim has already suggested. Then cut the circles into the sizes you want. Table circular saw with sled, used as above? The usual miter gauges with portable table saws aren't usually much cop for this sort of job. The greater width of the circular saw blade will take its toll on your stock material. A lathe with a parting tool will work but is also rather wasteful of material. All of the above will leave you with a fairly rough surface compared with gorgeous, snow white, 'virgin' sheet PTFE. Hence the "hours wasted" comment above.
  8. Rusted

    1"1/4 - 2" 'in line' adaptor

    The problem is not the EP "hole" but the gap between the moving drawtube and focuser casting. It was never like this in my day [last century] of push-pull RAS threaded focusing mounts!
  9. Rusted

    1"1/4 - 2" 'in line' adaptor

    It sounds good. The only thing I would ensure is that the open end is capped to avoid dust infall around the EP. I store my refractors on their dewshields in the workshop and often need an industrial vacuum cleaner to clean the sawdust off the backs of the objective lens. Even the focuser annular clearance is enough to leak micrometeorites. I should use individual poly bags over the focusers but they get such a bad press these days.
  10. Rusted

    Completed - fixed height hardwood tripod

    Fozzie, The problem with your spanning and filling between the lugs is that wood always shrinks as it dries. I'd be considering a solid aluminium spacer but the problem is getting it in there. Why not leave out the central "filler" section of timber altogether and add a sturdy 'ally' spacer instead. Properly done the central metal spacer will add to the structural integrity of the lugs and look "pretty" too. As if you had a solid metal extensions, the full width of both lugs, attached directly to the central boss. Just like the Vixen in your image above but even wider. Just as it should be on every tripod.
  11. Rusted

    1"1/4 - 2" 'in line' adaptor

    How do you ensure enough compression for guaranteed grip on the 1.25" diameter? There seem to be no other inward force than spring/flexure/resistance of the "flippers." A heavy load could still de-center your "flippers" because it relies only on their stiffness for both alignment and parallelism. What happens when you hang a bunch of stuff on the 1.25" diameter and then point a refractor at the zenith? Newton is very rarely wrong. I imagine partially split cones [collet style] would center the 1.25" nicely but would still need screw applied, opposing cone, end loading to ensure a safe grip.
  12. Rusted

    Completed - fixed height hardwood tripod

    Don't underestimate yourself, Fozzie. It's good to see anyone willing to have a go at a bit of ATM. I'd better explain myself: I was afraid you'd put a long bolt through both tabs of each leg. This would put enormous strain on the tabs which might give way. If you are sandwiching the tabs with wood then use a short bolt per tab. If you can find room to fit them in or can sneak a nut in between them. You could sink a nut into each "inner" leg then put bolts in from the outside if it's tight. A picture is worth a thousand [of my] words.
  13. Rusted

    Completed - fixed height hardwood tripod

    Call me old fashioned, but I really wouldn't start from here. If that cast, white tripod top is your intended donor I'd be putting the legs OUTBOARD of the lugs. And fit a LARGE METAL spacer BETWEEN the lugs to stop them snapping right off the casting when the cross bolts are tightened. The best tripods are very wide where they join at the top. A spreader in the middle can NOT stop rotational torque applied at the top when you move the telescope. It can only limit leg spread and provide somewhere to collect dew and dust on your exposed eyepieces. Think of each tripod leg as an inverted isosceles triangle with the base at the top. The wider the base of a triangle the stiffer it becomes laterally = vital torque resistance. The struts [legs] are ONLY put in tension and compression instead of literally bending. The wider the space between the bearings the smaller the potential slop using simple geometry. Stand on one leg and then try two. Two legs provide the vital triangulation for lateral stability. Your legs are put in simple compression to resist toppling over sideways. Bring you feet closer together and the stability drops. Ideally, hinged tripod legs should lock naturally against a flat surface up at the top. Were it me I'd be trying to emulate the lightweight, PORTABLE, folding piers you see under AP mountings. Hugely wide hinge spacing [triangle bases] mean broad triangles mounted on large diameter, hollow cylinders. Of course these are designed to fold for portability but the geometry is well worth studying. Drilling will not provide you with an accurate hinge bearing in wood. Or not for long as wood is sensitive to moisture. Cones are good because they will tighten to remove all slop. Spherical rod end bearings are relatively inexpensive for what they bring to the feast. [Think Go-cart steering components rather than cars] These can be bolted individually OUTBOARD of the tripod head lugs. This removes the danger of snapping off the lugs and maximized their spread. Bore the legs lengthways and epoxy the fixing nuts into the end of the wooden legs to allow some adjustability. Rod ends come in right and left hand threaded models with hexagonal aluminium arms.
  14. Rusted

    DIY rotating Nissen Hut or Pulsar 2.7m?

    Thanks, Kev. I too cannot wait to see it completed. Unfortunately the builder is given to melting like Odo when it gets much past 72F/ 22C. You just can't get the staff these days...
  15. Rusted

    Essential Mod for Pulsar Dome

    I feel your pain. One can only presume that Pulsar is basing its designs on the ergonomics of average medieval stature. The front door of our cottage was similarly afflicted as a torture implement, of the same period, until suitably modified. Fortunately, the only listing was related to the uprightness of its owner and the expletives it engendered on repeated cranial contact. One never learns to duck when one's attention is constantly AWOL. I meant to add that a quick spray with a high visibility paint [or tape?] might further improve your safety mod.
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