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Hi Rob.
I owned one of those Saxon 8" Dobs and yes the R+P focuser does develop some slack. I found the best way was to a do a complete clean up and adjustment. Secure the scope horizontally. Have an clean area set aside covered with newspaper. Undo the four screws holding a metal plate under the focuser knob and remove the pinion bar and retainer spring. They would be pretty mucky and will need a good brush in some kero. Loosen off the two tiny hex adjustment screws on either side of the locking screw at the top of the focuser. Remove the focuser tube and give the rack gear on the underside a clean with some kero. The focuser tube has a slippery coating which does wear out. I cleaned this with some metho then applied some quality car wax, buffed off then re-applied a few more times. Smear some clean grease to the gear rack then install the focuser tube. Adjust the tiny hex screws so they just touch the focuser tube. Grease to the pinion bar before installing. Screw the metal plate on but don't tighten it up yet! Now, using two hex keys, adjust the two tiny hex screws until they come in contact with the focuser tube then back off about one-tenth of a turn. Repeat this a few times then back off only enough as you would like it. Tighten the metal plate with the four screws until the spring tension against the pinion bar is on the soft side of firm. I hope this helps.
Cheers!
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