GSO RC8 Focuser side slop.

[mldee]

Has anybody else noticed the side-to-side (azimuth?) slop in the draw tube of the stock Crayford? It is still present on mine even with both upper (lock) and lower (tension) screws done up really tight.

I removed it today and found that there is excessive clearance in the little bottom "guide rail" assembly that the draw tube rides on, and with all tube support concentrated at the rear end, it gives the tube a lot of opportunity to "swivel" around that point, courtesy of that side clearance.

I will disassemble mine tomorrow and see what, if anything, is a practical solution. I would rather not do something that requires drilling holes in the casing, but who knows......

Has anyone else noticed this problem and are there any "quick fixes" that work?

I understand the real "quick fix" is to buy a Moonlight, but I'm a little stubborn.

[gbeal]

My quick fix was an adaptor, and 2" Feather Touch. Fixed it perfectly.
The less than ideal focuser, plus the significant amount of distance between rear cell and camera (I mean about 250mm, come on!!!) are enough to make me wonder who and why these were designed like this.
Great scopes though.
Gary

[mill]

I must be the lucky one then :P
My stock focuser on my RC is tight and doesn't go sideways.
I also have to use only the 50mm adapter and then the focuser only has to be turned out by about 2mm, so i have no sag at all :)

[Moon]

The only think I can think of is the guide rail is not screwed down tight enough onto the outside of the focuser. This has been reported by one other user I know of. Don't do it too tight or it will bend the guide rail and it will jam.
I've got 2 of them and never had the problem you describe.
James

[mldee]

That turned out to be the case. I opened it up this morning and noticed that the four little countersunk screws that attach the guide rail, which is actually a nice little linear ball race, were very loose. GSO QA seem lacking, but the fix was free....

A bit of experimentation with tightness as you said, and hey presto, solid as a rock in all directions. Also took a few goes to work out optimal tightness for the four Allen screws that hold the focusser shaft to the body, but eventually all came well.

BTW, for anybody who wants to check their setup, the optimal ball-race guide screw tightness on mine was just as the four screws started to feel firm. The test is to ensure the tube slides up and down freely with the focuser shaft assembly attached but its tension screw not tightened.

I have never had a problem with the 25cm spacing, the spacers provided are built like a tank and rock solid, and if you're going to have a Crayford style focuser plus an OAG plus a FW plus a CCD, 250mm seems about right. I'd rather have it that way than most cheap Newts with the reverse problem. My Megrez also needs a fair amount of junk hanging off the back, so it ain't just GSO RC's.

Overall, for my needs in DSO happy snaps, I find the RC8 to be a very acceptable instrument indeed. Beats my mirror flopping C8's. YMMV;)

Couple of pics attached for those who may want to check theirs.

[Moon]

excellent

[slang]

Most excellent indeed. I noticed the same problem, and had googled it several times to no avail. Even missed out on a second hand Feathertouch as a replacmeent...

Looked again tonight, found this thread, tightened my screws and tested. All AOK!

MOST EXCELLENT INDEED. Thank you very much!

Cheers -

[jjjnettie]

:) Excellent. Thanks for sharing the fix.
I'll have a look at mine tomorrow.