First small size Dob, advice please.

[wrinkly]

Bought a secondhand 8" Skyliner without finder at a reasonable price as my first small Dob, enabling me to go to town on it.

Completely stripped, mirrors washed, flocked, 9 x 50 right angle finder, well you want the best don't you , choice between Rigel and Telrad on the other side and lovingly assembled.

Took it out on the sack track to line up finders using the London TV masts. Found the scope sagging at low elevations, could be like me, just old age . Tried lighter fuel on the altitude bearings to get rid of possible polish, same problem. Now have two plastic pots Gaffa taped to tube with spare nuts and bolts achieving balance. Trouble is, it looks uglier than me .

Dob experts, what to do? Increase spring pressure by lowering the lower attachment point, higher grip bearing material and if so what, better balancing material or what did you do? As an OAP (aah bless) , impressed with the Orion Optics mount but have no wish to go on a starvation diet.

Finally, any recommendations for a plant pot mover to fit it and best way to clamp the two together.

Very appreciative of any advice.

[swamp thing]

Hi

I have those long magnetic knife racks on both my Dobs.

This allows plate weights to be placed anywhere along their length.

As the Dob becomes nose heavy simply place the plate weight on the magnet and slide along till balance is achieved. Job done.

Regards Steve

[Moonshane]

Steve's suggestion is a good one and a very quick and easy fix.

for me the skywatcher dobs are superb value and really excellent scopes but have one major flaw and one minor one, both to do with the bearings.

in my eyes, the alt bearing is far too small for trouble free use. also the az bearing could (can) be easily and relatively cheaply improved.

you sound like the sort of person who is quite handy so my recommendation will be based on this, especially as you will also presumably have some time available for a small project.

my experiences of dob mounts having made a couple myself dictate that a larger bearing surface will make for a smoother and more easily balanced system. this applies to both alt and az bearings but in this case more to the alt. ideally a bearing of a diameter not less than that of the main mirror size but certainly not less than 12" will always work well.

if I owned a skywatcher dob I'd probably make a new base out of plywood but would at least do the following:

1) glue a layer of laminate to the underside of the main mount housing. this can be obtained from smaller kitchen / wood merchants and should be as 'bobbly' as possible. I mean the sheets of stuff used to bond onto chipboard for kitchen worktops (less than 1mm thick). once dried and trimmed, wax it with car wax (preferably the thick wax in a tub) and polish off. this will enhance the left right movement substantially.

2) make some new larger diameter bearings for the altitude bearing. a single circle of plywood say 12" in diameter will create two bearings if cut in half. line the edges with the end trim for the above laminate and trim/polish.

3) fit to the tube mountings so the bearings sit outside of the base (a packer of the same ply may be needed.

4) cut some ply pieces to fit to the outside sides of the mount and cut a partial arc into them to match the bearings made above. glue/nail some teflon pads at points 70 degrees apart from the centre of the arc.

This will provide a far better motion for not a lot of cost - I'd estimate maybe £30 total if you have the tools. I created a couple of threads which might help you

http://stargazerslounge.com/diy-astronomer/140533-16-f4-orion-optics-uk-dobsonian-project.html

http://stargazerslounge.com/diy-astronomer/144997-home-made-dobsonian-base.html

[wrinkly]

Thanks Steve and Shane.

Being a totally non domesticated person, had to look up magnetic knife racks. See we share the same LGA member, Sewerage Works and in future, Incinerator although we hold different opinions on the best V8 motors.

Woodwork is generally a bit beyond me but will see if I can con a local carpenter into making the altitude 12" woodwork for a few pence and will try the extra layer of laminate. Both will help in trying to raise the whole caboodle a few inches in an attempt to save the back.

Who knows, if it all works out, might be able to find Polaris in the LP .

Thanks again guys, will let you know how it goes and if there is any plywood left over, will come in handy for my coffin .

[swamp thing]

Thanks again guys, will let you know how it goes and if there is any plywood left over, will come in handy for my coffin .

Always look on the bright side of life.

Regards Steve