Smoother Dob Rotation Please

[Rakanishu]

I bought a skywatcher 200p a few weeks ago and only been able to use it a few times (damn clouds)

But I find the mount rotation a little too stiff, it rotates but only with quite alot of force.

It would be nice to be able to spin it with a little less force.

Is there anything I can do/add to the mount to help with this?

Thanks

[Moonshane]

couple of things to check.

1. that the mails securing the teflon pads are below the surface

2. loosen your central bolt a little

I personally feel that adding a glued laminate sheet (from kitchen suppliers - usually less than 1mm thick) will smooth out the rotation a lot, especially after a coat of wax. adding a further teflon pad of the same thickness around the central bolt will help too.

some recommend lazy susan bearings but never used these myself.

[umadog]

Usually these Dobs are supplied with bad bearings to save money. Contact Beacon Hill Telescopes and get a new bearing surface. Likely you already have Teflon pads. It's the other surface that's causing the problem. If the surface is right it shouldn't even need lubricant. In my experience anyway.

[bendiddley]

Try adding one milk bottle washer (only needs to be couple of inches diameter, use the standard supermarket plastic bottles) below the main washer to raise it up slightly then put car polish on the underneath of the upper base plate in the tracks of where the teflon pads slide. This really helped for me. It's not 100% and it probably won't be unless you install a lazy susan but I didn't like the idea of that, it seemed like too much work for me. I can live with it though, its much better now. Good luck

[Weeman]

i might be able to help you here my dobsonian went very stiff about a month after owning it so i looked at the design off the pads that it turns on

so i came up with the idear of dropping 3 small roller bearings into the base board that the telescope board sits on top off

well i got to say the results are amazing it turns so easily now

heres a link to the bearings i used http://www.ebay.co.u...=item3363c1eccf

im going to try and put some pic but havnt a clue how being new here

[jimmyjamjoejoe]

Nice idea weeman.

I tried all the usual methods of different teflon pads, sheets of bobbly kitchen top stuff, washers of various sizes...

In the end, i got a lazy susan and never looked back. Seriously, these things should be standard issue (infact they are on skywatchers larger dobs). The motion was so free afterwards that i had to add some felt furniture pads to add a little friction, now it is absolutely perfect.

[pat]

When a lasy susan comes to mind I think of a spice rack. Maybe ours here are different. I can't picture how one would be used or attacted to the base. Maybe once I visalize it, it will make more sence. Pat

[jimmyjamjoejoe]

Thats right, the lazy susan is the bearing. Just 2 rings of metal with ballbearings between them. You sandwich it between the 2 base boards.

[stevetynant]

+1 for Jimmy - Lazy Susan has made a huge difference to the Azimuth movement on my 200p - incredibly smooth - still working out the best solution for the Alt movement

[Moonshane]

the irony with dobs is that the bigger the mirror (i.e. the greater the weight) the smoother and more stable the bases become. it's much harder to make a small dob rotate properly than a large one.

[umadog]

Yes, that's true Moonshane. Sumerian use Teflon & Ebonystar and that works well. My 10" weighs under 10 kg (and that includes the base) and the Teflon & Ebonystar is great on that on that. The Orion XX12 also uses that bearing combination to good effect. I had a friend who added Ebonystar to his Orion XT8 and has very impressed with the results. I think Ebonystar has been discontinued recently, although you can probably still buy some if you look.

I haven't tried the lazy susan. From what I hear, some people love it and some people hate it. Those who hate it complain it has too little resistance. It's possible that those individuals are using it on scope sizes for which it doesn't work well, they observe in windier conditions, or that they haven't adjusted the tension on it (which seems to be important).

[johninderby]

I use the Ebonystar and it does work exceedingly well.

I have done the lazy Susan mod on another dob and it does work well. The only tricky part is getting the height of the friction pads just right. You need the friction pads to add resistance by taking some of the weight of the scope otherwise it is unusable. You can make the movement as stiff or free as you want. I used three chair glides spaced around the lazy Susan bearing with thin plastic shims to adjust the height.

BTW Telescope Service still sells the Ebonystar in squares or pre-cut rings.

John

[Beulah]

Fantastic idea Weeman!

[jimmyjamjoejoe]

I use the Ebonystar and it does work exceedingly well.

I have done the lazy Susan mod on another dob and it does work well. The only tricky part is getting the height of the friction pads just right. You need the friction pads to add resistance by taking some of the weight of the scope otherwise it is unusable. You can make the movement as stiff or free as you want. I used three chair glides spaced around the lazy Susan bearing with thin plastic shims to adjust the height.

BTW Telescope Service still sells the Ebonystar in squares or pre-cut rings.

John

Thats why i chose felt over teflon to slow the lazy susan, getting the right height isnt critical since they're slightly squishy.

[Ganymede12]

I was given a lazy susan when I bought my 200P. I haven't added it to the scope yet though because it seems to require some other bits and pieces that I don't have. Or does it? Is it as simple as sandwiching it between the two ground boards?

[jimmyjamjoejoe]

I screwed it to the bottom board, obviously measuring and getting it central. That's it though, just plonk the other board ontop and put the bolt back.

The bolt is a little short with the added width of the bearing (adds about 7mm), but it still does up. I plan to replace it with an m14 bolt anyway, eliminating both lateral play, and the need for the little black tube it slides through.

[Rakanishu]

Where do I put the milk bottle washer? underneath the washer on the central bolt ontop of the dob base?

Just want to try the free solutions before paying any money to sort out the smoothness

[bendiddley]

it goes underneath the washer on the bottom plate. i made a few washers to start with as someone said they needed more than one, but mine seemed to work best with just one washer. you may need to experiment a bit with the tightness of the bolt as well. don't forget to polish the underneath of the top plate too.