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Further to my last post I should have mentioned that when using a Cheshire eyepiece to align the dot with the focusers' central axis it helps to use some device that accurately defines that axis. In its pdf Vixen suggests using a white paper disk with a small central hole that is inserted into the barrel of the focuser and I find that that works very well particularly if cross-hairs are drawn on the disk and the disk is rotated so that one cross-hair lines up with the telescope tube. The cross-hairs are easily seen because in daylight the paper disk is translucent. If a paper disk is not suitable for your setup you could instead use one of the longer Cheshire eyepieces that incorporate cross wires at the bottom end. The paper disk method is arguably more accurate as it eliminates any error caused by any "play" between the Cheshire eyepiece and the focuser draw tube.
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