Hi John,
I heard about the gauge method and even did some testing. Of course, my worm ring is slightly off round.
I will try to find some info about the worms on this forum, I did not see it before.
I think I am making some progress:
1. I swapped the worms but did not see much improvement, except that the PE curve was smoother
2. I reduced the tension in the belt and saw some improvement: the 480s period reduced from 13" to 7" and rest of the periods were very small, as you can see on the attached image
As a result, my guiding now is about 0.8" vs 1.5" in the past. Not perfect, but useable with my 1150mm scope. Stars are a little eggy, but they can be easily fixed using the deconvolution module of PixInsight.
Based on input from Guilherme, I will be trying direct-drive again.
