Club scope needs help!

[Rob_K]

Hope you don't mind me posting this here, as it's not strictly a 'classified' and it would be a shame to see it unnoticed elsewhere. The town of Bright in NE Victoria has a small group of keen observers and we regularly participate in 'outreach' stuff. Several months ago, one of the accommodation places in the district generously donated an old Saxon 8" dob to us. This scope had been neglected for many years, left outside in the elements.

One of our young members, Zac, made a project of restoring it, and thanks to his efforts we now have a pretty serviceable club scope we can use on outreach events, including school observing nights, local scout nights, etc etc.

However, the focuser is a beast of a thing with massive play that despite all attempts at shimming etc remains the Achilles heel of the scope.

Now in the end we'd be happy to go out and buy a basic rack-&-pinion focuser for it, but seeing that so many people who buy similar sized dobs immediately replace the r-&-p's with Crayford focusers, the group was hoping that maybe someone who has a redundant r-&-p for an 8" OTA gathering dust or being used as a door-stop might like to donate it to the club.

We could promise it a good home and we assure you that it would be put to very good use!! Just pm me - thanks!

Cheers -

[astro_nutt]

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!

[spacezebra (Petra)]

PM sent Rob

Cheers Petra d.

[Rob_K]

Thanks for those replies! Petra, I've pmed you, thanks. Astro-nutt, as far as I'm aware, Zac has had it completely stripped and re-assembled. The problem is that when we received the scope, the focuser was completely rusted up. It took a lot of work just to get it apart and it seems to have lost tolerances, hence the play. I haven't fiddled with it myself so this is just what I understand. Shimming improved it but it's still pretty woeful. It's such a big diameter barrel that any play gets magnified enormously - a very strange looking beast!

Anyway, still looking for a focuser for an 8" if anyone can help - thanks!

Cheers -

Rob