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Losmandy GM-8: Anomalous wearing of R.A. shaft

 

Hello everybody,
I have a GM-8 that I purchased new in 2000, which I have not used heavily;
so it is still quite new and behaving. Lately I noticed that the clutches
tended to slip, probably due to grease leakage to the nylon discs.?
So I decided to disassemble the mount
to perform a complete cleaning and regreasing. I started with the DEC axis
and everything was fine and OK. When I disassembled the R.A. axis I found that
the shaft shows signs of irregular wearing in correspondance of the upper
and lower needle barrels, on opposite sides of the shaft (see video). Only the
anodization seems to have come off and there are no signs of serious grinding.
Nevertheless, prior to disassembling, the axis rotated quite smoothly and
apparently there was no play whatsoever.
Does anybody have an explanation for what has happened and how to prevent
possible further damages?
Thank you all.
Sandro Barbanera
 

I explain the reason for this here:?/g/Losmandy_users/topic/relationship_between_needle/84580649?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,84580649

Peter
 

Sandro,

Not seeing your video. Did you post a link? Not sure if you can upload videos to this forum.

John
 

John,
yes, I posted a new message, this time with a link to youtube.
Thank you.
Sandro
Jim Waters
 

If this is the link I don't think there's much to be worried about.


Can you feel a deformation with your fingers?

------------------------
Jim W
Phoenix, AZ. USA

Losmandy GM811G, NINA 1.11, ASI2600MC Pro, Sky-Watcher Scopes
 

Sandro,

It is surprising that anodizing was used on a moving part, as wear would eventually remove the coating over time. In present day mounts, I think these shafts are all stainless steel. The patterns you see can be explained by the way the shaft rides inside the bearings, as Peter has stated, with some slight gap between upper and lower bearings. But if you are not seeing any problems with shaft rotation and you don't have any issues with problematic periodic errors, you are probably OK.? ?

The clutch discs can be replaced as the nylon wears down over time. But after cleaning you might try sanding them down with some 220 mesh sandpaper to roughen the surface a little. But after 20 years you may wish to get some new ones. Thoroughly cleaning where the discs ride with some solvent should also help a bit.

Best regards,

John

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