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AstroTech AT72 drawtube slipping

Started by paul.knight, 06/09/2014 04:46AM
Posted 06/09/2014 04:46AM Opening Post
I have an AT72ED--a beautiful little scope. Unfortunately the focuser drawtube has started to slip. I have tried adjusting the focuser thumbscrew, but I can only get it to either completely lock the drawtube in place or allow it to slip (especially with a heavy load like a binovue). Does anyone have any recommendations for how to rectify the problem? I would rather not take the whole thing apart blind. Thanks!

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paul.knight's attachment for post 58459
Posted 06/09/2014 07:49AM #1
Hi, Paul.

My understanding (certainly not guaranteed) is that the knob shown in the photo is for focus lock/unlock. There's a mechanism for focus tension adjustment via the hole "behind" that knob (above it, in your pic) - along the focuser shaft axis, in the "middle" of those four screw heads. I believe there's an allen screw in that recess. You might try the following:
1) back off the focus lock knob (make sure it's unlocked)
2) tighten the allen screw (tension adjuster) - just a smidge - checking & maintaining the focuser's ease & "feel" while you do so. (If it's too tight, you'll know.) I also recommend keeping your allen key engaged with the allen screw and noting its position (ala clock hand) relative to the scope/focus assembly, *before* you do any tightening, just in case you want to undo any adjustments you try.

The tension adjuster and focus lock do work together, so that may be all you need to bolster the focuser's capacity.

Take care, and best wishes.
-Dan