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RA Tracking Spikes

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#1 JohnW*

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Posted 26 October 2013 - 04:08 PM

To the group,

I have an AP 400QMD which tracks fairly well according to PHD and PECPrep. I routinely get 0.04-0.05 rms in PHD (Autoguiding) and average 0.5 arc sec in PECPrep analysis. However, I also routinely get transient spikes as high as 6 arcsec. Is this a worm issue, ie high spot etc. or some other problem?
Any advice would be greatly appreciated.

John

#2 orion61

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Posted 26 October 2013 - 04:33 PM

You could try Lapping the gear. It sounds like a high spot,
How often do you get it?
You may have 2. I lapped one on a Starfinder. I just used my Electric drill and valve grinding compound. It tracked MUCH smoother!

#3 JohnW*

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Posted 26 October 2013 - 05:11 PM

The spike happens about once every 4 worm cycles.

#4 Whichwayisnorth

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Posted 26 October 2013 - 09:08 PM

Does it happen with regularity? Can you post a PEMPRO plot? I wonder if there is a dirty bearing somewhere that is catching and then breaking loose.

#5 Whichwayisnorth

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Posted 26 October 2013 - 09:10 PM

You could try Lapping the gear. It sounds like a high spot,
How often do you get it?
You may have 2. I lapped one on a Starfinder. I just used my Electric drill and valve grinding compound. It tracked MUCH smoother!


I've always wanted to try this using the Time Saver yellow can for soft metals but I am not sure how to do it without taking everything apart then I would worry that I was lapping at the wrong pitch angle and make it worse not better. I'm still tempted though.

#6 JohnW*

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Posted 26 October 2013 - 09:42 PM

Your bearing idea may be a good one. I went back over some old PE plots and at times it would guide with spikes no higher than 1-2 arcsec. It is a very old mount circa 1990's. I did adjust the play 3 years ago to reduce backlash. Maybe just a really good cleaning and re-grease. Which brings up another question as to which grease to use?

#7 JohnW*

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Posted 26 October 2013 - 10:10 PM

Here is a typical graph of PE

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#8 blueman

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Posted 26 October 2013 - 11:04 PM

Lapping worms is not a beginners job, I would suggest you think twice about that.
Have you cleaned the worm wheel and worm and regreased it? You may have dirt in the grease.
Blueman

#9 orlyandico

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Posted 26 October 2013 - 11:56 PM

I have a 1990s AP600E QMD. Probably of the same vintage.

SuperLube is highly recommended, but AP recommends Lubriplate 105, which is cheaper (but I can't find any).

#10 JohnW*

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Posted 27 October 2013 - 10:41 AM

Blueman and Orly,

Thanks for the info. I agree, the first step is to clean and regrease the gears and then go from there. At short focal lengths it performs well but, I would like to go out past 1000 with an at6rc.

#11 blueman

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Posted 27 October 2013 - 12:46 PM

Yeah, I am not familiar with that mount, but I have seen dirt cause this issue in others including my AP900. It is sometimes windy and the dirt just gets into everything.

I just made a new cover for the pier and will try to keep mine cleaner. Last week I cleaned and regreased the AP900.

Make sure to turn the worm with your fingers to make sure the bearings are OK and not dirty or sticky. Also check the gearbox and clean and lube it if that mount has one that is accessible. When the worm is off, move the mount to check the bearings there too, they should be very smooth and move easily.
Blueman

Blueman and Orly,

Thanks for the info. I agree, the first step is to clean and regrease the gears and then go from there. At short focal lengths it performs well but, I would like to go out past 1000 with an at6rc.



#12 JohnW*

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Posted 27 October 2013 - 05:09 PM

Blueman,

Thanks for the heads up on dirt in the gears. Here in AZ we get a lot of fine dust. Both axes rotate very freely so I dont think the bearing are worn, even being so old. The gearboxes do come off with the motors. AP build, what can I say. This was a big improvement over the Orion Atlas and Meade LXD 75.

John

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#13 blueman

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Posted 27 October 2013 - 05:44 PM

Yeah, we are the same here, hot and dry with some winds and of course the ever present dust devils.
I had a very similar problem with my MI-250. I found a lot of grit in the grease and after completely cleaning it and putting fresh grease the problem was eliminated.
Blueman

Blueman,

Thanks for the heads up on dirt in the gears. Here in AZ we get a lot of fine dust. Both axes rotate very freely so I dont think the bearing are worn, even being so old. The gearboxes do come off with the motors. AP build, what can I say. This was a big improvement over the Orion Atlas and Meade LXD 75.

John








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