Lazy Susan Dobsonian Mount

[Mandy D]

I have just bought a new Skywatcher 300PDS and am planning to put it on an aluminium Dobsonian style mount. Has anyone used a lazy susan bearing for the azimuth turntable? Is it smooth enough? Here is a link to the bearing I am considering:

https://simplybearings.co.uk/shop/p183585/390mm-Round-Lazy-Susan-Rotating-Aluminium-Turntable-Bearing/product_info.html

I suspect that my turntable will be about 600 - 650 diameter, based on the 520 diameter used for 150 - 250P tubes.

[cajen2]

It's the standard az bearing for the StellaLyra dob range. I had the 8" dob and I loved the bearing. If possible, have a knob to alter stiction or lock it.

[Mandy D]

Just now, cajen2 said:

It's the standard az bearing for the StellaLyra dob range. I had the 8" dob and I loved the bearing. If possible, have a knob to alter stiction or lock it.

Thank you. That is everything I needed to know. I plan on having a clutch / brake. I can now sit down and design it.

[cajen2]

Excellent.

[Mr Spock]

Here's what I have on my 12". Works perfectly.

[Mandy D]

@Mr Spock That's pretty much what I found and linked to. Do you know what diameter you used?

[Stu]

I’ve used this one before, I think it is higher rated as the bearings are between the horizontal surfaces, rather than in the groove between the two rings if that makes sense?

 

[Mr Spock]

6 minutes ago, Mandy D said:

Do you know what diameter you used?

600mm

[Mandy D]

@Stu that makes perfect sense as it is a thrust bearing, so carries the load better in a horizontal orientation.

[Mandy D]

@Mr Spock Are your supports for the tube a long way out so they sit over the bearing? I'm planning to have mine as close to the tube as practicable, so a smaller bearing would make more sense for me.

[skybadger]

9 minutes ago, Mandy D said:

@Stu that makes perfect sense as it is a thrust bearing, so carries the load better in a horizontal orientation.

But a taper roller is better at centering and those flat plate ones have more slop than the ring ones. I have both and much prefer the ring type. It's currently carrying my 18". The flat one is also quite noisy. I have not lubricated it yet though. 

[Mandy D]

@skybadger yes, I agree a taper roller will self-centre and also carry end thrust. Are you using a single row ball bearing type under your 18" like Stu is?

[Stu]

15 minutes ago, skybadger said:

But a taper roller is better at centering and those flat plate ones have more slop than the ring ones. I have both and much prefer the ring type. It's currently carrying my 18". The flat one is also quite noisy. I have not lubricated it yet though. 

I just found that if I tightened the centre nut up too much to get the right tension, they get quite notchy, the other kind didn’t for me. I didn’t find any slop either . I guess they aren’t expensive so Mandy could always try both?

[Mr Spock]

32 minutes ago, Mandy D said:

Are your supports for the tube a long way out so they sit over the bearing? I'm planning to have mine as close to the tube as practicable, so a smaller bearing would make more sense for me.

Here's the base on the bearing.

And here's the whole thing.

No space left over 

These bearing do come dry, so you have to grease them. Once done you can tighten the central knob as much as you need and it remains really smooth.

[Ratlet]

14 minutes ago, Mr Spock said:

Here's the base on the bearing.

And here's the whole thing.

No space left over 

These bearing do come dry, so you have to grease them. Once done you can tighten the central knob as much as you need and it remains really smooth.

I should probably have checked mine.  Never greased it lol.

I stuck a teflon pads (b&q ones for sliding furniture) stuck back to back in the the centre.  It provides just a hint of friction when tightening the central knob and was just the right thickness.

[Mandy D]

@Mr Spock Ah, I see what you have done now.  Thanks. I'm going to wait until my OTA arrives, then I can get the measurements I need directly off it. I think a range of bearing sizes could work well for this, as long as the uprights are supported adequately. Your azimuth bearing tension adjustment looks neat. I like that your tube just drops into the altitude bearings. A lot of good ideas here. I have more facilities for metal working, so I am going to stick with making it from aluminium. I can cut weight by removing metal where it is not needed.

[mr_belowski]

Mine's on a lazy susan (8 inch dob), done by the previous owner, and it doesn't have a clutch or a brake and is a pain. Smooth, but unless I stuff my plastic mobile phone case into the gap it wanders around all over the place. Don't skimp on the brake / clutch

[Mandy D]

1 minute ago, mr_belowski said:

Mine's on a lazy susan (8 inch dob), done by the previous owner, and it doesn't have a clutch or a brake and is a pain. Smooth, but unless I stuff my plastic mobile phone case into the gap it wanders around all over the place. Don't skimp on the brake / clutch

It will definitely have something to hold it on target. That is one of the aims. I think Mr Spock's idea of a central bolt to control pressure on the bearing looks viable.

[bosun21]

I can second the roller bearing that Mr Spock detailed previously. Once lubricated it's extremely smooth throughout. I have the same scope as him with the centre tensioner screw.

Edited August 1, 2023 by bosun21

[mr_belowski]

I did try with a bolt through the middle to add some tension / vertical load to the bearing but it made it a bit sticky. I think it needs some proper friction material

[Mandy D]

Just now, mr_belowski said:

I did try with a bolt through the middle to add some tension / vertical load to the bearing but it made it a bit sticky. I think it needs some proper friction material

I will look into that when I build mine. I need it to hold rock steady for photography.

[cimh]

Hello - I'm new to this thread. I picked up a used skywatcher 200p dob this week - tried it tonight and the two things I really do not like are 1. the finder scope & 2 the rotation bearing in the base (or the lack of one) which makes it so hard to nudge smoothly, I have tried adjusting the central bolt and putting some silicone on the sliders but with no real improvement. Certainly inferior to my skywatcher heritage 150 I guess partly because of the greater weight of the 200.  The red dot finder on the heritage works much better for me so I will add one of those. But I like this idea of the lazy susan and will order one - I would love to hear what size is likely to work best on this scope - I thought the largest diameter that will fit on the base will be best but Mandy D I can see the logic of putting it as close to the base of the supports as that is where the weight is?

I'd love to see a picture / diagram of a way to add friction to the system that would be great

 

[Spile]

50 minutes ago, cimh said:

Hello - I'm new to this thread. I picked up a used skywatcher 200p dob this week - tried it tonight and the two things I really do not like are 1. the finder scope & 2 the rotation bearing in the base (or the lack of one) which makes it so hard to nudge smoothly, I have tried adjusting the central bolt and putting some silicone on the sliders but with no real improvement. Certainly inferior to my skywatcher heritage 150 I guess partly because of the greater weight of the 200.  The red dot finder on the heritage works much better for me so I will add one of those. But I like this idea of the lazy susan and will order one - I would love to hear what size is likely to work best on this scope - I thought the largest diameter that will fit on the base will be best but Mandy D I can see the logic of putting it as close to the base of the supports as that is where the weight is?

I'd love to see a picture / diagram of a way to add friction to the system that would be great

 

I am surprised about this. My Skywatcher 200P hasn’t had any treatment since new as I didn’t want to risk contaminating it. I agree that the finder needs replacing though and that is why I changed mine to a RACI and Telrad.

[cimh]

9 hours ago, Spile said:

I am surprised about this. My Skywatcher 200P hasn’t had any treatment since new as I didn’t want to risk contaminating it. I agree that the finder needs replacing though and that is why I changed mine to a RACI and Telrad.

Thank you Spile. It surprised me too - I struggle to think skywatcher would sell something that's so difficult to nudge smoothly. I didn't put it together as it was used but it looks to be in perfect condition. It has the 3 rectangular teflon pads around the edge and the disc one in the middle. So that seems right  -perhaps dust or maybe the silicone spray made things worse  so I'll clean it all up and try again before going the lazy susan way.

 

[John]

I have recently acquired a 200P dob as well. I've not owned one for over a decade. Mine was practically unused and I've made 2 changes to it:

- replaced the straight through finder with a 9x50 RACI one. That is my usual finding arrangement with my scopes.

- cut a large diameter "washer" from a plastic milk carton and placed that between the teflon washer supplied with the scope and the bottom board of the mount. This takes a little of the weight of the scope off the teflon pads which makes the azimuth movement a lot smoother and almost eliminates jerkiness altogether. Some folks find that 2 of these milk carton washers are needed but in the case of my scope, one did the trick.

Otherwise I'm very pleased with the scope. Optically it is excellent - I had forgotten just how good these things are 🙂

I had a couple of dobs in the past that had lazy susan bearings (8 and a 12 inch) but found those too loose in azimuth movement so I had to install friction pads to counter that !

Dobs always seem to need some tweaking in my experience, annoying though that can be 🙄