az/dob bearing mod

[danielsun]

Just thought i'd let any dob owners who might not know this , know how to get the ultimate in azimuth smoothness. On my 10" i thought i had a pretty smooth running az base with teflon washers and shiny pot plant i.d. cards cut out as washers with silicone spray. But me being a compulsive modifier a had to try better. So i took the outside diameter of the nylon bush that links and rides between the base plate and rocker box and measured the gap between the two bases which was 3.5mm and for $15 went to CBC bearings and got a thrust washer set that fits nicely over the bush .Basically its just two 1mm washers and a needle roller race that goes between them. And to stop any sideways slop which was only a few mm i wraped plumbers teflon tape around the outside of the nylon bush so that it would be a nice hand press snug fit. The other thing i had to do was lift off the three outer teflon slide pads and shim underneath them to the same height as the thrust washer thickness ( because the thrust washer was 4mm thick) and (the teflon pads were 3.5mm thick) using pot plant i.d. cards as shims which were 1/2mm thick, exactly what i needed! i also did away with the staples and screwed the
teflon pads and shims to the base using tiny scews.i put the bolt back through and nipped it up without overtightening and WALA!!! THE BASE IS NOW SUPER SMOOTH!!! much much better than before. It feels that good that i did my 8" too!!!

[cristian abarca]

Can you show us a picture of it?Regards Cristian

[danielsun]

Hi cristian! yes, ive just got myself a new camera and i'm having trouble compessing pics small enough to post. but i'll take a few pics and hopefully post some shortly. ;)

[danielsun]

Here are the photos I promised you, hope you can make sense of this and it helps.

Image 313 is the teflon pad

Image 314 is the thrust washer set and the nylon bush wrapped in teflon tape
to take up any side ways slack

Image 317 is the bush and the thrust washers assembled ready for the rocker box to go on top with the 'pot plant id card' (card that comes attached to plants when you buy them) I used as shims under the teflon pad

[cristian abarca]

Thanks for the pictures. I like this modification and I'm going to try it after the Australia day weekend . It should work pretty well on my heavy mount and it should remove the rest of the jerking.( Somewhere in the DIY section I posted pictures of my homemade telescope). I'll keep you informed of how it goes.Thanks.Regards Cristian

[Roger Davis]

What stops dust getting into your needle roller?
Using virgin teflon (as opposed to other non-virginal teflon usually supplied) and making a washer to fit in the middle helps.
There are also things called "pivot kits" available from some places that are a beautifully made bush that replaces the "average" supplied AZ Dob bearing.
The pivot kit also has a bored head on the retaining bolt to fit encoders.
Great idea to replace all your teflon pads with real teflon, any teflon that has a peel and stick side is not virgin teflon. It is not easy to etch teflon to take an adhesive.
The use of brass screws is a good one. Any visible wooden surfaces should be sealed with Estapol or similar.
The use of "Ebony Star" formica or a stippled laminate surface will bring about a better movement of the azimuth axis. Polishing and buffing the tracking surface with Armoural helps as well (and I mean buff! don't leave it wet and expect it to work!)

[danielsun]

I could make a nylon washer to go over o.d of the needle roller to act as a protective case, but i dont think dust getting into the needle roller would really be a major concern. It is covered by the large diameter discs of the rocker box and base plate that i think any dust would be minimal.

[Roger Davis]

Been there, dusted that ...

[janoskiss]

... :rofl:

Roger, the teflon on the bases of the GSO dobs is virgin teflon, right? (I still haven't used the three pads you got for me, but maybe I will as the bigger pads might work better.) BTW, any news on the Orion 127mm Apex. :poke: I'm coming to hassle you in person soon! :P Time to get me a good wide TFOV EP, I think.

[anthony2302749]

For those who own a Dob and wish to modify it, like we are doing here or who wish to build their own. “The Dobsonian Telescope” by Kriege & Berry, it is a must have book . It will answer all your questions plus a lot more.