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Re: accuracy of glass artificial horizon figure
From: George Huxtable
Date: 2008 Aug 22, 11:39 +0100
From: George Huxtable
Date: 2008 Aug 22, 11:39 +0100
Bruce Hamilton asked- George: I clipped the information below from an online tool catalogue. How little money would I have to spend to buy two levels accurate enough to calibrate a glass sheet (or mirror) horizon? Horizontal-Mount Levels N 5/8" Dia. x 3 3/4" Lg.0.001520 sec./2mm0.228"Brass (Black Finish)2160A5$76.30 N 5/8" Dia. x 3 3/4" Lg.0.0051 min./2mm0.228"Brass (Black Finish)2160A763.04 N 5/8" Dia. x 4 13/16" Lg.0.0072 min./0.1"0.196"Chrome-Plated Brass2160A196.98 P 13/16" Dia. x 6 3/8" Lg.0.00036 sec./2mm0.375"Brass (Black Finish)2160A2171.20 Q 2 15/16" Lg. x 9/16" Wd. x 9/16" Ht.0.03315 min./0.050"0.156"Aluminum2160A327.80 Q 2 15/16" Lg. x 9/16" Wd. x 9/16" Ht.0.03315 min./0.1"0.156"Polycarbonate (Black)2160A410.30 Q 2 15/16" Lg. x 9/16" Wd. x 9/16" Ht.0.12245 min./0.1"0.156"Polycarbonate (Black)2160A9*��9.50 Q 2 31/32" Lg. x 9/16" Wd. x 37/64" Ht.0.12245 min./0.050"0.156"Polycarbonate (Black)3329A46 10.30 R 2 5/32" Lg. x 29/64" Wd. x 21/64" Ht.0.1851 sec./0.1"0.079"Brass (Black Finish)2160A3611.95 R 2 5/32" Lg. x 29/64" Wd. x 21/64" Ht.0.1851 sec./0.1"0.079"Brass (Chrome Finish)2160A3711.95 R 2 1/2" Lg. x 1/2" Wd. x 5/8" Ht.0.0051 min./2mm0.125"Brass (Black Finish)2160A1177.20 R 3 23/64" Lg. x 5/8" Wd. x 3/4" Ht.0.0051 min./2mm0.125"Brass (Black Finish)2160A672.92 =============== Although Bruce addressed the question to me, I doubt if I am the best fellow on this list to answer him. To be honest, I've had little experience in using levels and artificial horizons. And I'm unsure about some of the sensitivity numbers Bruce quoted anyway, as two columns appear to have run together, and there seems to be little correspondence between them. What exactly do those columns represent? I fear that, copied once again here, those tables have suffered further mutilation. However, let me make some guesses. Clearly, for this job, a highly-sensitive level is called for. The one at the top of Bruce's list, if I follow his numbers right, at 20 sec per 2mm shift, appears to fill that bill, at $76.30. But there are other matters to consider, such as how accurately the tube has been set into the base, and how uniformly it's been ground, for smooth movement of the bubble, and whether the glass plate will be big enough to accomodate the span between its feet.. Bill Morris rightly asked why two levels would be called for. What he didn't point out, because it's so obvious, is that you should always try a level both ways round, and take the average. Bill wrote- "The levelling screws end in ball bearings. One of them sits on a plane , one in a conical depression and one in a vee groove machined in bits of brass let into thesub=frame." Clearly, and this has become inreasingly apparent from his postings, here we have a real expert, with a full understanding of kinematic design, and an asset to this list. However, I'm a bit uneasy about the way his mirror sits on "a bed of thin felt" . Is he quite certain that when he lifts off the level, after setting the plate horizontal, the felt doesn't spring back, just a touch, when its weight comes off? That might be checked by adding a corresponding bit of extra weight while keeping the level in position, to see what happens.. ================ And Gary LaPook has added- "I have been taking series of shots of Jupiter in my artificial horizon (since it is favorably placed) and I want to takeseveral more series then I will write up what I found." Gary has a mercury horizon to use and that's undoubtedly the best, although there are problems. You can alternatively use water, or better, dark oil, or molasses (which here we call treacle), but those are difficult to use with all but very bright stars, and very clear nights. However, Jupiter is presently very bright, and those liquids could well be usable with Jupiter, if anyone wants to do the same as Gary. George. contact George Huxtable at george@huxtable.u-net.com or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---