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Rusted last won the day on April 19

Rusted had the most liked content!

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1,335 Excellent

1 Follower

About Rusted

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    Sub Dwarf

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  • Interests
    ATM, imaging, solar, Solar system, photography, blogging, cycling, walking, audio, DIY, clocks.
  • Location
    Exiled to sunniest and darkest, rural Denmark!
  1. Good score! The Green Cross Code has obviously worked well for you. You should definitely stay away from "The Express" click bait headlines. Every single day, something is "out to get us." Read on down and it all proves to be complete nonsense. The Express used to come up as a suggestion on Google News. They were obviously aware of my interest in astronomy. TMA! Too Much Advertising! So I stopped being taken in and now I'm almost back to what passes as normal. Ticket prices to the Ark?? If you have to ask...
  2. Adding anything on top of a curved tool will increase its radius of curvature. It follows that grinding will remove the outer regions first. Ceramic isn't that hard under the glaze. Steel washers and Araldite used to get a good press. I cut up thick glass into squares. Then used pitch to stick them onto a 16" pre-curved, dental plaster tool. The plaster was too soft even after gentle baking and a nightmare to clean up between grades. A metal disk from a scrapyard would be my choice of tool these days if I couldn't afford a plate glass tool. Plate glass has the advantage of being softer than "Pyrex." So "boulders" will be crushed into the plate glass surface first. Use less abrasive for a sharper but shorter cutting action. Too much powder and it just grinds together and turns to mud. Be guided by the noise. If there is any with your plaster and ceramics? Glass on glass rings nicely. You could play it by ear. Even if you were tone deaf.
  3. Well, Ron, if that is your attitude you're definitely not getting a return ticket on my Ark. Have you noticed the subtle irony of your signature from one sporting 29,000 posts? Do as I say not as I do?
  4. Even after 60 years of amateur astronomy I still learn something new here every single day. Mind you, at my age, every day is a surprise. SGL can be anything you want to make of it. Treat it gently, feed it regularly and you will gain lots of knowledgeable friends. The best thing is that they don't all want to come round and borrow your stuff. Most of them just want to share their obsession.
  5. Survival of the fittest? Don't even get me started.
  6. It's no use getting theoretical. We've already lost the plot .
  7. A decent straight edge and feeler gauges will put you close to your desired sagitta. I just used a suitable length, stainless steel rule on edge and measure the gap in the middle of the mirror. Try two or three rules in the shop edge to edge against the light. Reverse the test edges in turn. It's a null test for straightness if several edges match.
  8. Tell me about it! They outnumber the rest all put together.
  9. Let's not generalise too much for the sake of our younger members. What you describe only occurs where the observatory resides at the bottom of the garden.
  10. Mine is still a baby and I'm it's great, great grandad.
  11. It would not be difficult to fit a shaped scraper or stiff brush to sweep the channel clean with every movement. Using two different profiles is clever. Such a system has been used for ages on lathe beds to avoid friction. One way guides mercilessly while the other supports the loads. There is no sideways movement for the channel wheel to cause wear. Lathe beds are subject to constant and highly abrasive debris and use scrapers and felt pads for cleaning and lubrication of the ways. The wear from [typically] infrequent uses of an ROR, even over decades, is unlikely to cause any visible damage. On your other point: A V-profile would have higher point loading than closely matching radii. In practice the materials are usually hard and inflexible enough to ignore the difference. I would imagine twin, V-profiles would require much tighter building tolerances if subject to typical twisting forces. Since both rails are desperately trying to steer. Matching radii wheels and tracks would mean that the wheels ride up the curvature of the walls if there is the vertical freedom to do so. Though both are still trying to steer. Causing increase friction unless one set of wheels are allowed some sideways float on their rail. Or words to that effect.
  12. Thanks Alex. You appear to have captured your very own occultation of Saturn by the Sun.
  13. Thanks. Every little helps when things completely defy logic and experience.
  14. The risk of lung disease from making a mirror, or two, pales into insignificance when optical workers, who used rouge, could be followed home just by their red foot prints.
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