Balancing the AVX
Posted 23 August 2013 - 08:19 PM
Now that I've had my AVX for a few weeks and got to try it out a few times, I am a little perplexed on how to balance it in contrast to my CGEM. The gears seem a little stiff, even when RA and dec are completely unlocked. I need to nudge it with a little force just to line up the markers. I put my TMB 92L on it and by gosh, no matter how high or low I put the 11 lb counterweight, there is no telling if the mount is properly balanced. In contrast, my CGEM is so smooth with the RA and dec locks unlocked, that mount doesn't need hypertuning, but my new AVX is quite stiff!
Any thoughts would be appreciated.
Oh yeah, one more thing that may or may not be related to this issue, this mount is quite "loud" when slewing to an object.
Posted 23 August 2013 - 09:35 PM
Posted 23 August 2013 - 10:00 PM
i loosened it up a little by spinning it back and forth on the RA after loading it up. did the same thing with dec, but it's still a little stiff.
Posted 23 August 2013 - 11:41 PM
The AVX mount is very different from the CGEM. In the CGEM the ring gears ride on ball bearings and the axes ride on a ball bearing and a taper bearing. As a result, except for when the ring gears are not fit well in the housings or there is too much grease used (or both), the CGEM axes can turn relatively freely. In the AVX on the other hand, the ring gears ride directly on metal to metal (both raw aluminum) bearing surfaces while the RA axis rides on one ball bearing and a metal to metal bearing surface with a ball thrust bearing to hold things together. The DEC axis rides completely on two metal to metal bearing surfaces. When the RA clutch is released on the AVX, the metal to metal contact between the ring gear and the axis casting and the metal contact between the axis casting and the axis housing creates a lot of friction which is only partly reduced by the presence of the single ball bearing. The amount of grease used (usually too much) and the fit and finish of the contact surfaces make things very stiff. The same thing happens on the DEC axis only worse since there are no ball or thrust bearings at all. While this can be improved with a lot of work, the mount will never move as freely as the CGEM, particularly in DEC. The CG-5 mount has the same general design as the AVX and the same issues in this regard.
As a note of caution, EFT just finished working on an AVX where someone had sprayed WD-40 into the mount to try to loosen things up. Don't do this! The result was that the grease was dissolved and the DEC axis metal to metal bearing surfaces were destroyed either by debris washed into them by the WD-40 or by something to do with the WD-40 itself.
The choice with this mount is to either leave it as is and use whatever method you can to get close to balance, or tune it up to make it easier to balance, but it will not be easy.