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Re-greasing the Astro-3 equatorial mount

 Up one level

I bought the Lidl-refractor in December 2005.  I have equipped the Astro-3 equatorial mount with a Vixen MT-1 motor in the RA-axis. The purpose is to use it as a light-weight travel mount. Pictures of the assembled mount and a description of how I mounted the motor to the equatorial head is described in another page.

Greasing

The original grease used by the factory is more like glue. I decided to replace this grease. This is a fairly simple operation.
Start by removing the cover for the worm gear:


Here we see the gear of the RA-axis,
 


and the various parts of the worm drive (after cleansing in white spirit).



Remove the cover at the bottom of the RA-axis by loosening the screw indicated by arrow.
 


Loosen the nut with a 17mm wrench.
 


Pull out the assembly.
 


Detail of gear-wheel (after cleansing). It has 138 teeth. However, I have heard reports of samples with 139 teeth as well. If you plan to motorize with computer control you should know this number for calculating correct speed.
 



The bearing-housing of the RA-axis. The upper bearing is plastic. The løower bearing is just a hole in the metal bottom of the housing.
 



All parts of the RA-axis assembly can be released by loosening the locking screw  in the upper part of the picture.  Pull out the gear. Clean the parts in white spirit and apply a grease suited for the temperature range where you live. I used the grease shown below:
 


It should be useful from -30o C til + 150o C.

Then, put all pieces together. When you thighten the nuts that fasten the RA-axis and the worm-drive axis you have to be careful not to use too much force. If you use too much force the drive will not rotate easily. If you use to little force, the mount will be unstable. The axis should run freely, but with a firm feel.

The Declination axis can be dismantled by removing the worm gear housing, loosening the 2 locking screws in the big nut with the setting circle.
 


Declination axis, nut with setting circle and 2 locking screws.


 

Pull axis out of the housing, clean all parts and apply new grease. Put all pieces back together. Again using just the right momentum to ensure that the axis revolves freely but without slack.
 

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© 2006 Odd Høydalsvik