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G11 worm wobble

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#1 Jinux

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Posted 16 September 2020 - 10:34 PM

Hi,

 

G11's worm block issue is well known agony and my G11 is not an exception.

I put some shim under worm one side of worm block to make motor and worm aligned. 

As well known, this is impossible task as there is no reference plane to make this perfectly aligned, so I just tried my best but they're not and have no way to know which side to push if it shows wobble as there is no reference plane, again.

 

I measured worm wobble using dial indicator. In one worm rotation, total wobble is measured as 0.0005"pk-pk. 

But if I measure old-ham coupler, it's another story of wobbling like ~0.007" pk-pk and I'm not even sure whether coupler is really round enough.

And the way dial indicator move is similar to how PE looks like, so what it matters is alignment on old-ham coupler.

Do I understand correctly?

And how much accuracy do we need on old-ham coupler wobble? 

Once I disconnect coupler, I can see motor shaft has less than measurable wobbling. So it's all coming from coupling alignment it seems.

 

Thanks for your advice!

 

Jinux

 



#2 Jim Waters

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Posted 16 September 2020 - 10:37 PM

Have you posted here?  How old is your mount?  I haven't seen wobble reports for a long time..!

https://groups.io/g/...dy_users/topics


Edited by Jim Waters, 16 September 2020 - 10:48 PM.


#3 Jinux

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Posted 16 September 2020 - 11:14 PM

Thanks for suggestion! I'll post there too.



#4 StephenW

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Posted 18 September 2020 - 09:48 AM

>And the way dial indicator move is similar to how PE looks like, so what it matters is alignment on old-ham coupler.

>Do I understand correctly?

 

Yes, the motor-coupler-worm alignment will impact PE, but it's (usually) not the primary source of PE (that's usually determined by how out of round the worm itself is).

 

Not an apples-to-apples comparison, but I had the same challenge on my Parallax HD150 (it uses the Losmany motors, Oldham coupler and Gemini).

 

I spent a lot of time getting the motor shaft as aligned as possible with the coupler and then the coupler with the worm.  As yo have seen, wobbles in the coupler will impact overall PE.  Getting the motor-coupler-worm aligned knocked 10" off my base PE for that mount (bringing the uncorrected PE down to about 20).

 

How much effort you want to put into this really depends on what your final imaging results look like after training PEC and guiding.   Even with 20 arc/s uncorrected PE, with PEC applied I was getting 7arc/s, and with guiding I was usually around 1 arc/s RMS.  Not stellar, but good enough for what I was doing then.

 

So I guess the question is what do your final imaging results look like and do you even need to bother spending a lot of effort trying to get everything perfectly aligned?



#5 Lola Bruce

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Posted 18 September 2020 - 11:08 AM

.0005 on a dial indicator?

 

What does the outside diameter eccentricity have to do with gear face accuracy?



#6 Jinux

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Posted 18 September 2020 - 05:24 PM

.0005 on a dial indicator?

 

What does the outside diameter eccentricity have to do with gear face accuracy?

Eccentricity is not what I was trying to measure.

 

Based on the link below

 

http://www.wilmslowa...m#bearing_block

 

If I see worm wobble, it could be indicator of having 'tight spot in the bearing race', and dial indicator was my way of attempt.

May not show what I intended though.




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