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Jim,
I agree about tightening only one setscrew on the tool. You want the tool to be pressed into a linear contact with the wall of the focuser drawtube, just like the eyepiece. I'm lucky because my Catseye tools fit so tightly in my focuser they have to be twisted into the drawtube--tightening the setscrew makes no difference in collimation.
But in those focusers with a little more slop, I don't think it's practical to maintain a constant inward pressure on the tool to keep it seated in the focuser (and not tip due to gravity). And, as I've commented, I've seen one too many focusers not cut squarely at the top (and, quite recently, a focuser with only the top 3/8" of the drawtube having 2" I.D. and the rest about 1/16" larger!!!).
I like the idea of pressing the tool into a linear contact with the drawtube so it points exactly the same direction as the drawtube. Of course, this won't work if the hole in the drawtube isn't concentric and colinear with the O.D. of the drawtube, but that's a defective focuser anyway, and you shouldn't plan for that.
I guess my point is that there is a lot of slop in the typical telescope system, and leaving the tool loose just adds another bit of sloppy tolerance. I think repeatability demands a slight tightening of the setscrew in most applications. Bird's post just reinforces my thinking on that subject.
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