This is not an engine

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  • Member since
    March, 2008
This is not an engine
Posted by Antitax on Sunday, January 12, 2014 11:04 AM

   My dob is a 12" GSO, of which the Zhumell and Apertura are clones. The tube has two large short plastic cylinders on the sides; they rest inside the mount against teflon pads, and provide the up-and-down motion. I tried lubricating them with spray-on silicon lube, that was very ok, but felt heavier than the left-and-right motion, eventhough it bears the full 30 kilos of the telescope while the up-and-down axles bear only the 20 kilos of the optical tube.

   So I switched to 15W-40 engine oil on the up-and-down moving parts. It felt definitely lighter but after a week or so the cylinders showed a bit of marring, maybe the oil was chemically attacking the plastic, I'm not sure. I switched to silicon lube again after smoothing the bearings with a wet kitchen rough sponge. A few dozen passes around the cylinders, cleaning the teflon pads, the maintenance of a fully manual dob takes close to nothing.

   Now the up-and-down movement feels a bit heavier but it doesn't backlash and stiction is barely there. So, don't experiment with mineral oil, plastic doesn't like it. Maybe another type of silicon lube will make it slicker, but from now on I won't try stupid marriages; plastic requires dedicated lubricant, mineral oil is a no-no. Since candle wax on teflon works fine in the left-right movement, I will also try it once the silicon on the up/down bearings dries up.

Tags: wrong idea

TS 8x40 Wildlife, 10x50 Marine/Fujinon 16x70/TS 80mm triplet, 6x30 finder, EQ-3 mount, TS 2" 99% diagonal/Celestron C5+ and 6x30 finder, DIY tripod/5" Bahtinov/12" GSO dob, 8x50 finder/Meade 2" 24mm 82°/Hyperion 24,13,10mm 68°/TS Expanse 17mm 70°/SW 7mm Panorama 82°/Ultima 2x barlow/Astronomik UHC-E filter/Baader O-III/Astro Solar 5" & 80mm filters/Sky Atlas 2000/Rükl's Moon Atlas/Canon 400D/5mW green laser

  • Member since
    March, 2008
Posted by Antitax on Monday, January 20, 2014 1:14 PM

   Update: the spray-can silicon left little crusts of dried grease after some days, and motion became stiffer and stiffer. So I wiped it off and rubbed a silicon rag on the trunions instead. This is a rag that was offered as a freebee with issues of Guns&Ammo and Handguns. They recommended applying it to guns or fishing gear to protect against corrosion, it's not supposed to be a lube but it works so well as a lube for the trunions' shiny plastic, I had to rebalance the scope.

   Now both axes are equally smooth, the remnant of stiction is gone, totally gone, so much so I can now feel the front end of the tube takes a tiny little more force to move up than down. Tomorrow I'll buy a pack of twenty 36x10mm steel washers, once attached to already present counterweights, they should make the rear heavier enough to make balance perfect, even when the off-axis mask is on.

   I think some rags for shining car bumpers also leave a silicon film, if your dob's altitude motion is not smooth enough, that might be your solution. Candle wax would probably not work at that place, better leave it for the base where the plastic is different and rougher.

Tags: finally

TS 8x40 Wildlife, 10x50 Marine/Fujinon 16x70/TS 80mm triplet, 6x30 finder, EQ-3 mount, TS 2" 99% diagonal/Celestron C5+ and 6x30 finder, DIY tripod/5" Bahtinov/12" GSO dob, 8x50 finder/Meade 2" 24mm 82°/Hyperion 24,13,10mm 68°/TS Expanse 17mm 70°/SW 7mm Panorama 82°/Ultima 2x barlow/Astronomik UHC-E filter/Baader O-III/Astro Solar 5" & 80mm filters/Sky Atlas 2000/Rükl's Moon Atlas/Canon 400D/5mW green laser

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