rehab a G11
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Hi Bob,? The teardown, cleaning, and re-lubrication is easy to do.? You'd need a few common chemicals (maybe degreaser from local auto parts store).? Anyways, its easy to do.? The needle bearings have tiny like 1/8th inch diameter rollers, and these need to be easily rolling.? Old grease tends to "gum" the rollers with a coating of "varnish" and this is where the automotive degreaser chemicals can dissolve those varnishes.? The harsh chemical "Berryman B12 Chemtool" is one such powerful degreaser.? To use that, you must work outdoors for fresh air, and wear heavy rubber chemical gloves, and use metal pails (this chemical will dissolve?plastic too).?? To clean the needle bearings, you'd unscrew the clutch knob (start with DEC axis on the top), and remove the parts.? Note the order they are assembled, or else look at Mark Crossley's website:? ? for his recommendation for parts order.? That works better for most owners and for me.?? Start by removing the DEC axis dovetail from the mount. After you lift out the DEC axis 1.25 inch shaft, you will see the needle bearings... upper and lower.? Try rolling the needles with your finger if you can reach in.? If those feel hard to roll, you'd put a rag into the bottom of the axis, put a pail below the end of the axis, and pour in some of that Chemtool B12 and let the chemical do its job.? The rollers will come free.? Then after all is dry again, re-lube.? Many people suggest using Superlube with "syncolon" but that is really teflon.? Or I use lithium based spray grease by CRC that you get at the auto? store.? Any of these will work just fine to keep those needle bearings rolling smoothly. This is a good time to also clean the plastic clutch disk area.? That area tends to get oils from the bearings that creep in to the surfaces, and of course, once oils are there the clutch will not hold..it will slowly creep under any kind of imbalance.? Or contact me for high friction clutch disks that will hold much better and seal out the oils or moisture.?? Then...do not yet reassemble the DEC axis.? With the DEC axis off, remove the RA axis and repeat the cleaning for the RA axis.?? Then reassemble the RA axis, then the DEC axis. You do have to lube the worms too to reduce the rubbing metal to metal friction as much as possible.? There are good lubes for this.? If you are in a warm location like me, the grease recommended by the factory is Artic Jetlube.? However, from the specs on friction alone, there is a better low friction grease: CRC Brake and Caliper Grease sold at auto parts stores.? You must paint that grease into the teeth of the worm wheel (aka ring gear) all around.? Then the worm.? Then assemble the worm so its threads are inserted well into the ring gear teeth.? Then gently push the worm inward, and cinch down the left and right bearing blocks.? While you are doing that inward motion on the worm, also you must compress the worm along its axis so the worm blocks (their tiny bearings on either end of the worm) hold the worm from left to right motion.? In this way you eliminate?the time lags (hysteresis) in the drive mechanism.?? Once the worm is adjusted and its worm blocks locked down, test the mount drives using your Gemini (if so equipped).? If you have a tucked motor system, you can adjust the spur gear to spur gear mesh by shifting the gearbox position on the lower spur gear.? If you have a spring loaded worm system, you must also adjust the worm "back off bolt" so that the heavy spring does not put undue friction on the worm to ring gear rubbing surfaces.?? I find it best to use an ammeter on the DC current going into the Gemini, in order to have a "dashboard" for these adjustments.? If the ammeter shows the Gemini motor current going way up, I know that the drive threads are in too tightly.? The motor current is also a good way to judge an imbalance in each asix.? You put the axis horizontal and slew the motor back and forth in direction, and if there is an imbalance, the currents will be different.?? That's not all, of course.? There are recommendations to "supertune" your mount and I've described those in various writings. No sense repeating those instructions here.? If you need some of those supertune parts, let me know.? ? Work on these mounts, even old ones, have demonstrated a PE down to under 1 arcsec RMS.? It can be achieved, but takes some elbow grease and upgraded parts like superior worm bearings.? These parts are quite reasonable in price.?? Don't be daunted... the mount is a simple design, not an automobile automatic transmission!?? All the best, Michael On Tue, Aug 30, 2022 at 3:34 PM Robert Hancey <rdhx@...> wrote: Bob Hancey here, have received some posting for rehab work. May well be the path to repair, but working for success at this point, but the mount may require more than my skills i.e., professional/ divine intervention. Respectfully submitted --
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Michael Herman