OD Dobsonian Lazy Susan upgrade

[Stu]

I’ve struggled with the az axis of my Orion Optics OD Dobsonian base since I got it, very stiff movement that makes fine control of position very difficult. I often use it on an EQ mount to minimise the amount of adjustment needed but still it is a pain.

I found a lazy susan bearing on eBay and though I would give it a go. I had to move around some of the spacers so it sat correctly on the three legged base, but that aside it was a simple (and reversible) change to make. All that was needed was to put the central PTFE bearing in the hole from the top rather than up from the bottom, and find a longer bolt of the same thread and size.

First impressions are very pleasing, free movement that allows fine control of the position. Hope to try it out tonight.

[AdeKing]

How are you finding this mod after 6 months @Stu? 

I seem to remember reading on another thread that the bearing had worked rather too well and that you needed some additional friction.

How did the mod evolve?

I've just started using my Skywatcher 8" Dob again after its sat unused in the Summerhouse for a couple of years.  Its been mounted on an OOUK Dob Base and I've found exactly the same as you, the AZ motion is a right pain to use at high magnification with far too much stiction causing me to either not move enough or to overshoot, either way very frustrating.

I'm keen to try this mod, but am interested to know how you solved the lack of friction problem.

Ade

[Stu]

On 07/11/2020 at 20:42, AdeKing said:

How are you finding this mod after 6 months @Stu? 

I seem to remember reading on another thread that the bearing had worked rather too well and that you needed some additional friction.

How did the mod evolve?

I've just started using my Skywatcher 8" Dob again after its sat unused in the Summerhouse for a couple of years.  Its been mounted on an OOUK Dob Base and I've found exactly the same as you, the AZ motion is a right pain to use at high magnification with far too much stiction causing me to either not move enough or to overshoot, either way very frustrating.

I'm keen to try this mod, but am interested to know how you solved the lack of friction problem.

Ade

Hi Ade,

Sorry for the delayed reply, kept meaning to then not finding the time!

The mod is certainly better than it was before, but I’m not 100% happy with it. The bearing I used doesn’t like being tightened down too much and gets jerky in its movement. I need to find another way of adding some resistance but haven’t worked that out yet!

I think with a larger scope there are more suitable bearings around, but I can’t find any for my skinny little 8”.

Still a work in progress, the movement is not how I would like it currently.

[markse68]

On 07/11/2020 at 20:42, AdeKing said:

I've just started using my Skywatcher 8" Dob again after its sat unused in the Summerhouse for a couple of years.  Its been mounted on an OOUK Dob Base and I've found exactly the same as you, the AZ motion is a right pain to use at high magnification with far too much stiction causing me to either not move enough or to overshoot, either way very frustrating.

Hi Ade, @Chriske mentioned a really clever idea to reduce friction/stiction of the az bearings of dobs  which might be worth playing with? Basically it involves adding a primary thrust bearing of small diameter inside the existing ptfe pad arrangement so that it takes most of the weight and the outer pads only really act to balance the scope. Being smaller diameter the effect of the friction on the smaller thrust bearing has much lower impact on the rotational drag. Haven’t tried it but it does sound to me like it should help 

Mark

 

[Stu]

Just to update this, I found a much more suitable bearing which I have just fitted and it seems much better. I am able to tighten the centre bolt down more and it stays smooth. Once this awful run of rain ends, I’ll give it a go!

https://simplybearings.co.uk/shop/advanced_search_result.php?keywords=lazy+susan+bearing

I bought a 12” one for eventual use on the 12” truss dob I still need to finish doing up. Yet another unfinished project!

[callisto]

Wow....did know you could get these bearings up to 990mm 😮