Advice needed - I stripped the screws behind my secondary mirror. Skywatcher GoTo Dob

[hippriest90 (Laurence)]

Hi guys,

I own a Skywatcher 12" Collapsible GoTo Dob. I haven't used it in years since moving to an equatorial mount and a smaller reflector tube. The last time I used it however I had troubles aligning my secondary mirror because it appeared that I had stripped the screws behind it.

Recently I've been thinking about using this telescope again because it has been sadly neglected over the years or potentially selling it to somebody who would appreciate it more than myself. Before doing either of these things however I was hoping somebody could point me in the right direction to replace these screws. So my questions are: Is this possible? and where could I purchase said screws?

Apologies if this is somewhat vague. If needed I can upload some photos of the screws I am talking about.

Laurence

[mental4astro (Alexander)]

Hi Laurence,

These screws are typically M4 in size, by however long. If it is just the screw thread that is stripped (how did you manage that!?!), just remove one and head off to the hardware store and find a stainless steel set to match.

I am surprised that the screws have been stripped. This means things have been WAY over tightened. The secondary assembly is a delicate structure. Things will move - that's the nature of the beast as things vibrate during take down, set up and transport.. Over tightening to attempt to stop this is asking for trouble... . We are not fixing a wheel to a car. I'm not chiding, just sharing a cautionary word .

Check also that the threads inside the spider hub are not damaged. Before replacing the old screws with the new, grab a bunch of cotton buds & with some metho clean out the hub threads. This will remove any metal filings that will be problematic.

Mental.

[hippriest90 (Laurence)]

Thanks for the advice! Glad to hear they're standard screws that are easily obtainable. I just checked the spider hub threads and they seem to be fine.

To be completely honest, I bought the telescope in a foolhardy rush. I didn't do enough research beforehand and failed to educate myself properly on how to use and maintain the telescope resulting in unintentionally stripped screws.

[rustigsmed (Russell)]

Hi Laurence,

how about upgrading them so you don't need to use a screwdriver?
http://www.bobsknobs.com/Newt/page66/SWdob.html
makes collimation so much easier!

Cheers

Rusty

[hippriest90 (Laurence)]

Those look great. I think I'm more inclined to sell this Dob at the moment, however I may have to consider purchasing these for my 8" reflector. Thanks for the heads up!

[MattT]

To add to Alex's post...Bunnings don't sell the SS screws your after. Masters do, at least in M6 size... haven't needed m4, if that is what you need
You might need to re-tap the threads in the secondary which means an m4/5 or 3/16th tap possibly, or whatever Tool retailers...All Tools etc....ie not bunnings sell single taps of higher quality than the low quality taps sold by Bunnings.

Have you really stripped 3 screws?

Matt

[pmrid (Peter)]

I've had a similar problem with a newt that would not hold collimation. It turned out that the collimating screws were not stripped but the small brass insert in the spider assembly through which one of the collimating screws was threaded was slipping in its mounting. Turns out the spider assembly was plastic and the female thread component just glued in place inside the plastic body of the spider. Pretty shoddy work all 'round. I ended up replacing the whole spider assembly with one that is better made and stronger too.

Peter