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G'Day Barb and David,
My guess is you are probably doing the right thing, just not enough of it...
Drift aligning can be very frustrating to learn, because most people worry about adjusting too much. I know I did. But the key is to start by making big adjustments, then when the star drifts the opposite way, you know you have gone too far... but you also know that proper alignment is in between your last two adjustment points!
Then you can start making smaller adjustments! I usually try to apply something like a binary search method to achieve alignment quickly.
I'll describe how big my initial adjustments are to give you some idea. I usually align with a star diagonal and a 10mm illuminated reticle EP, so for my scope I use the Right Hand Rule: if the star drifts in the direction of my right thumb, I adjust the azimuth to push the star in the direction of my right fingers. Since you are using a newt, you would apply the Left Hand Rule (star drifts in direction of LH thumb, adjust in direction of LH fingers).
For my initial adjustments, I adjust the azimuth till the star is nearly out of the FOV, then bring it back onto the Dec cross hair with the controller, adjust again, and bring it back onto the Dec cross hair... and keep repeating this until the star is on the Dec cross hair at the edge of the FOV. Then I use the controller to centre the star in the middle of the cross hairs again and check for drift.
Once I go too far (i.e. star starts to drift the other way), I adjust the other way by half this amount - i.e. till star is 1/2 way between centre and FOV of the Dec cross hair. Try to make each adjustment from there on half as big as the previous one.
My guess is though, that since you reckon your tracking is good for 10 minutes, but not for 20, then you should be pretty close. Maybe try an adjustment 2 or 3 time bigger than you've been doing just to prove you are as close as you think. If it doesn't drift the opposite way, you just need to go further.
Another thought too... since you appear to be close, have you gone back to check your latitude adjustment? It might be worth doing that at this stage, before you try for final azimuth alignment. It might be out enough to affect your alignment in az.
Hope this helps!
Al.
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