Dob goto base seized

[CarolandDom]

Hi,

I have a Sky-Watcher Skyliner 300P FlexTube GOTO which I am enjoying however after a period of no use the base has become very stiff. My fault, as it became wet not realising that the cover I had bought for it was not waterproof.

Looking through the threads in here I found one which I followed to try to strip down the base however I have become stuck at the point of trying to remove the motor housing from the base after removing the 4 machine screws. I suspect that it is a combination of corrosion and the base material swelling which is preventing me from removing the motor from the base. When I release the worm gear from the static gear using the release lever the motor turns easily which is what is fuelling my suspicion.

Any advice or suggestions would be useful as I've come to a halt in my investigation for the moment. It looks to me like I'm going to need a new base which may be a better bet anyway as the original supplied is heavy and definitely not good in the damp.

Dom

[NGC 1502]

 

Hard to be sure without seeing the mount, however -

The SW Dob mounts are made from particle board which is ok if it doesn’t get wet.....as you mention the cover is not waterproof ( was it left outside ? )and you suspect swelling, that would seem to suggest that’s the problem. You could leave the mount to dry thoroughly then recheck, but usually if particle board has swollen because its got damp it stays swollen.

Are you into DIY ?  You could rebuild the mount with exterior grade plywood and seal it, and if well done would be better than the original and lighter too. If you go that route, you could cut around the motor, and with a bit of work, detach it.

Just an idea but could perhaps be a solution.  Or you could see if you can purchase a replacement mount, seal all edges prior to assembly, run mastic into the joins after assembly, then keep it as dry as possible.

Hope you sort it, Ed.

[CarolandDom]

Hi Ed,

Thanks for the reply - I'm fairly sure it's particle board. Yes it was left outside...I know, not my best moment.

I can be into DIY. I suppose if I was careful how I cut the motor out I would have a template to work from (the existing base). Having a lighter base would be a strong positive. I don't suppose anyone out there has a template or drawings with dimensions?

If I go down the plywood route.I will try to post pictures here.

Cheers,

Dom

[NGC 1502]

 

Hi again Dom.  Using the original parts of the mount as templates would be a good idea. You’d need to be careful if the plywood was a different thickness to the original partical board, the drives on the motors need to mesh properly. But shouldn’t be too hard to sort that. If the ply was thinner, spacers between motor and wood should fix that.

Although not directly relevant, this https://stellafane.org is a great source for DIY for telescope building.

Good luck, Ed.

[CarolandDom]

Hi Ed

I've made up a cutting template and a parts bill of materials in case any more of the bolts shear when I disassemble the existing base (One of the bolts holding the motor to the upper base sheared when I tried to remove it leaving me holding a head and part of the bolt body - well rusted).

I'm considering either birch ply (and treating it thoroughly) or marine ply for the base material. The existing base is 18mm thick or very close to it which will be very close to the new material.

I am considering using an alternate bearing (to replace the teflon setup) - perhaps a large lazy Susan type setup and the original thrust bearing is a bit of a mess so I will need to replace that also.

Might need to borrow a jig saw or router from family/friends to work with the original pieces as templates.

Then there is the challenge of cutting out the motor from the upper base board whilst leaving a recognisable template behind and damaging as little as possible around it.

Thanks for the wishes!

Dom

[Waldemar]

Don't try to use a router when you do not have experience with it. They are kind of tricky and need some 'know-how.
Because of the high speed and therefore high momentum involved they can be quite dangerous.

Maybe the owner can lent you a hand instead of the machine... he has experience with it.
Of course the shearing bolt experience taught you to use stainless steel bolts, but they brake easier than the rusting ones... so a little precaution won't hurt