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LXD75..RA dissassembly, grease

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#1 MtnGoat

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Posted 17 October 2008 - 03:21 PM

I'm ready to go in to the RA axis and do some polishing and attend to the obnoxious dragging I feel on one side of the RA axis.

It is totally interfering with setting up my RA worm properly...loose enough in the draggy orientation is backlash city in the not dragging orientation.

In addition, I can hear the motor change speed when it passes through this zone. In a rate based system lacking feedback on the actual axis and using open loop position calculation, this is the kiss of death for positioning accuracy.

Where is the danged RA nut hidden...under the polar scope circles or something? I suppose I'll find it, I just prefer not to screw something up dorking around with it.

Grease...their grease is nasty, sticky, and gritty (used mount). I have a NAPA up the street in this metropolis of 1000 souls. White lithium OK?

thanks

#2 MtnGoat

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Posted 17 October 2008 - 07:52 PM

Ok, so I found the stinkin' RA grub screw hidden underneath the RA setting circle collar, both accessible through the RA collar set screw hole. Great.

Now I can unscrew the RA nut partway and the axis comes loose, but I can't get it off over the polar finder housing and I can't find a lockscrew for that piece and it won't unscrew.

#3 usnao95

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Posted 18 October 2008 - 08:20 AM

you should be able to unscrew the bolt and the the whole housing should come right off, at least thats what i think your doing, i've been wanting to take it off again but its been so clear over the last 4 night i dont want to chance anything right now, but i used white lithum grease last time, i just didnt clean off all of the sticky grease that was on there, i gotta get around to doing this soon, huge week long star party starts next week up in Cheifland, fl. im at work now but when i get home i can help you out more on what your doing, i work better when i can see my mount.
Eric

#4 Skywatchr

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Posted 18 October 2008 - 09:34 AM

MtnGoat, Use a strap wrench on the polar finder collar. It will unscrew but is pretty tight. You can use pliers, but you'll scratch it up. Use SuperLube or Mobile One red synthetic grease. I use SuberLube myself, but the Mobile One is fine too. I used kerosene and a brush to wash off all the old "glue" grease and then washed everything in hot soapy water. After drying completely, I then go ahead and inspect, polish, and deburr as necessary. Then wash in soapy water again before lubing and reassembly.

Jeff

#5 MtnGoat

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Posted 18 October 2008 - 10:31 AM

Well, you're both right. I finally found a description of just unscrewing it and the savage locktite they applied, and sure enough, off it came. Not until totally marring the *BLEEP* out of it with the wrench. :{

Why the H E double toothpicks they slop this thing with locktite when the RA collar is doing all the work, I have no idea. I will not be locktite-ing it back on.

Oh well, as a bonus at least I also damaged the chrome hour circle.

So I cleaned out all the sticky grease, and replaced with white lithium since I hadn't seen any replies until this morning. Now that I know how to get it apart and the finder stuff is pre gouged for my convenience, I'll see how that works and be able to go to another grease fairly easily.

I am convinced my RA drum gear is slightly out of round, by the way. I had to back way off on the worm in order to not have it binding, and it's noticeably stiffer in two places 180 degrees apart.

#6 Skywatchr

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Posted 19 October 2008 - 09:36 AM

No doubt the drums are out of round. The RA and DEC locks work by putting pressure on the drums. If they get overtightened they can squeeze them to be out of round. Storing the mount with the locks tight can do that. Try having the locks just tight enough to have a slight drag and turn the mount manually until you "feel" the high spot against the lock screw. Then crank the lock tight a few times to try and squeeze it back to being closer to being round and let it set tight for a while. Then do it at 180° again. It may help some. Too bad the RA and DEC drums aren't interchangeable. Sometimes the DEC is "better", but it won't fit the RA axis.
Oh, and Meade is famous for using LockTite! :lol:

Jeff

#7 MtnGoat

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Posted 19 October 2008 - 10:39 AM

Thanks for the tip on the drum being out of round. In some ways the drum approach is interesting..in others it shows some weakness. I'm at the point now where I am wishing they'd just have used regular gears.

#8 Project Galileo

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Posted 27 June 2009 - 09:30 PM

Hey goat. I am now hypertuning an LXD75 I got on the cheap locally. After also doing the LXD55 I now am 2 for 2 on marring due to locktite. I am begining to look at the scars as the mark of a corrected mount and would look for them in the future as a bonus beauty mark.

#9 Jimmy2K63

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Posted 28 June 2009 - 12:56 AM

So when parking the mount just leave the lock knobs a little loose at all times and things should be fine? That's not a problem. What are they - like bands on an automatic transmission or something?






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