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Old Meade Starfinder EQ too shaky...

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#26 hottr6

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Posted 19 January 2014 - 09:49 AM

Comments on your photos:
1) The Vixen dovetail is too small for this rig. Either go back to the lightweight Starfinder straps or a wider dovetail.
2) The "gap" in the DEC axis is for the optional tangent arm (bright shiny thing in following image)

Posted Image

3) The "gap" under the RA setting circle appears about right
4) I kept the stock DEC clutch screw and it works fine.

#27 hottr6

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Posted 19 January 2014 - 09:54 AM

Keep the nylon bolt. Anything else (except brass) will mar the shaft, causing shifting when clamping. Not good!!!!

As for the RA axis gap, it can be taken apart, but it's tough! There are plastic bushings inside you can grease while you are in there. It's fairly self explanatory once you start stripping it down. You may need a small amount of mass persuasion (small dead blow hammer) to bang the shaft out.

Pulling the DEC axis should require NO persuasion. It is held in place by a small grub screw on the saddle. Relieve the grub screw and the nylon clutch screw and the DEC axis will fall out (watch your toes). If not, you may have a bent or abused shaft.

#28 schluterdude

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Posted 19 January 2014 - 02:00 PM

I agree with a well loved one! The plastic bushings are fairly snug. I was able to obtain one with virtually zero hour on it (but still 20 years old! Lol) and whatever grease was used at the factory had "stickified" over the years.

I'm not saying to bang the snot out of it. Yes, something is VERY wrong if that is the case. A small rap with a 3lb dead blow just helps get the process started if his was like mine. Clean up the old grease, clean the shaft with WD40 and a grey scotch brite pad, and slide her back together!

#29 Chopin

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Posted 21 January 2014 - 03:28 PM

Okay, I've replaced the huge industrial casters with some small furniture grade casters. Now I can raise the casters off the ground with blocks and have a perfectly solid meeting point right from the base. Another positive side effect is that the whole pier is now 5 inches lower, improving the center of gravity. Much better.

Second thing, I pulled off the weak saddle. Until I can justify the cost of a full saddle and plate (maybe ADM), I'm just bolting the tube rings right to the top plate of the mount. It works, even though it's not as elegantly adjustable. Definitely solid, though. Another improvement.

So now it seems apparent that the most obvious amount of remaining jiggle is emanating from the RA axis. It's not a lot, but it's definitely there. so the next step is to pull off the cover and see if the worm gear needs adjusting. I'm not sure exactly what "backlash" is. But if it's a degree of wobble between the teeth and the worm then I can see how that might be an issue.

I'll get back once I strip and assess it.

#30 rdandrea

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Posted 22 January 2014 - 12:52 PM

I'm not sure exactly what "backlash" is. But if it's a degree of wobble between the teeth and the worm then I can see how that might be an issue.


That's what it is.

#31 Dr. Woo

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Posted 23 January 2014 - 10:00 PM

Yeah my Starfinder GEM has slop in the (backlash) in the worm and gear too. Haven't tried to adjust it out yet, but there is a screw to adjust that.

And to obin robinson I'd love to see pictures and info on your stepper conversion being as the motor is missing on my GEM

#32 obin robinson

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Posted 24 January 2014 - 07:16 AM

Yeah my Starfinder GEM has slop in the (backlash) in the worm and gear too. Haven't tried to adjust it out yet, but there is a screw to adjust that.

And to obin robinson I'd love to see pictures and info on your stepper conversion being as the motor is missing on my GEM


Send me your e-mail address and I can send a bunch of photos to you in high res.

obin :)

#33 schluterdude

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Posted 24 January 2014 - 09:33 AM

Every gear requires a small amount of backlash. With the gear being plastic, I'll bet that there's a ton of runout/out of round to it as well. This is why you "cheat" and intentionally leave the RA axis slightly out of balance, so you are always in a loaded condition.

#34 Chopin

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Posted 26 January 2014 - 08:32 AM

So, I pulled the plastic housing from the gears at the back of the RA shaft. There might be a little backlash there, but it seems okay.


Every gear requires a small amount of backlash. With the gear being plastic, I'll bet that there's a ton of runout/out of round to it as well. This is why you "cheat" and intentionally leave the RA axis slightly out of balance, so you are always in a loaded condition.


I can acknowledge that when I don't put slightly more weight on the "dropping" side of the RA it can take roughly 5-10 seconds for the image to start tracking again after I reposition the RA by hand. Perhaps someone here knows if this is within normal tolerances for the Starfinder. Mine seems like it's 14 years old, given the instruction booklet has a copyright date of 2000.

At any rate, I've viewed with the scope twice now since removing the sloppy saddle and the jiggly casters, and I'm disappointed by how much worse the vibration is at the RA. Settling times are noticeably faster, but the vibrations are higher in frequency. I understand basic mechanical principles enough to get why this is happening. And after inspecting the whole RA "arm" (not sure what the correct name is) I can verify that it is indeed the weak link.

I tested my theory by closely watching the gear and electronics housing while moving the scope end manually and forcefully back and forth on the RA axis. It clearly flexes in opposing directions, ever so slightly, in response to the scope on the other end. I wonder if the real culprit is that the joint that holds the RA "arm" in place is just too weak to handle the loaded 28.6 pound OTA and 25 pounds of weights on the lower shaft. If this is the case, is there a way to strengthen the RA axis?

#35 schluterdude

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Posted 26 January 2014 - 02:05 PM

Do the vibrations match the frequency of the motor vibrating and/the small gearbox? Is there a resonance building up causing the tube to vibrate like a tuning fork?

#36 herrointment

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Posted 26 January 2014 - 02:14 PM

The clutch does have some lag in it so you need to lead the object you wish to observe a bit. You can try adjusting balance and clutch tension......it's a can of worms though. Here's a LINK for replacement bushings if that's any help.

Some folks are really liking this mount.....so the answer is out there somewhere. Good luck!

#37 schluterdude

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Posted 26 January 2014 - 02:59 PM

When setting balance, disengage that slipper clutch! I forgot to mention that earlier! I think there are three screws on the tension plate. You can always completely remove it, clean it up, and re grease it as well. Then use a marker, and mark the tube for both visual and AP setups. That way you can just set it and go each time.

#38 Chopin

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Posted 26 January 2014 - 07:30 PM

Do the vibrations match the frequency of the motor vibrating and/the small gearbox? Is there a resonance building up causing the tube to vibrate like a tuning fork?


No, I believe they're much slower frequency vibrations than the motor, and they only come on when I touch the tube or when a moderate breeze hits it like a sail. It does eventually settle (less than two seconds, perhaps). The worst part is that it sets off vibrations every time I touch the focuser knob. It is making it extremely frustrating to dial in the correct focus since it vibrated every time. Maybe I'm expecting too much out of the mount. I'd like rock solid performance, and I beginning to think I'm not going to get that with a 45 inch, 28 pound OTA. I'm still willing to work with it, though, because I'm not in a position to drop $1500-2000 on a new mount.

#39 Chopin

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Posted 26 January 2014 - 07:33 PM

The clutch does have some lag in it so you need to lead the object you wish to observe a bit. You can try adjusting balance and clutch tension......it's a can of worms though. Here's a LINK for replacement bushings if that's any help.

Some folks are really liking this mount.....so the answer is out there somewhere. Good luck!


Thanks. I really like the mount, it works wonders with my 4" Newt. Tracking is really good for visual use, and it runs on AA batteries. Hard to complain about that for the $50 it cost me.

I'll check the link and see about the clutch.

#40 Chopin

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Posted 26 January 2014 - 07:33 PM

When setting balance, disengage that slipper clutch! I forgot to mention that earlier! I think there are three screws on the tension plate. You can always completely remove it, clean it up, and re grease it as well. Then use a marker, and mark the tube for both visual and AP setups. That way you can just set it and go each time.



Good tips. Thanks, T.

#41 schluterdude

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Posted 26 January 2014 - 08:05 PM

Perhaps try a motorized focuser?

Or, try and reinforce the area around the focuser. I have a thin steel plate on both the OD and ID of the tube that shores up that area, helped me out allot!






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