I love these DIY engineering solutions – terrific article mate!
A bit off-topic, but you’ve got me thinking – would the lazy Susan be strong/smooth enough to be used as the azimuth rotation on a motorised bino seat, with the full weight of the observer, chair, mount and binos?
A bit off-topic, but you’ve got me thinking – would the lazy Susan be strong/smooth enough to be used as the azimuth rotation on a motorised bino seat, with the full weight of the observer, chair, mount and binos?
Dennis,
You would be pushing the friendship with that combo. The weight would be too much for the thin housing as well as the overhang as the bearing is only 300mm diameter and your base would be at least a metre.
I love these DIY engineering solutions – terrific article mate!
A bit off-topic, but you’ve got me thinking – would the lazy Susan be strong/smooth enough to be used as the azimuth rotation on a motorised bino seat, with the full weight of the observer, chair, mount and binos?
Cheers
Dennis
Hi Dennis,
Thanks for your comments.
These 12" diameter bearings are rated for 230Kg axial load without binding, if you apply a little light grease to the ball race. Some data sheets even mention 1000 lbs, or 300 Kg.
They are not however rated for any sideways load at all. I think the main problem in your application would be stresses on the bearing cage introduced by off-axis loads and tilt, such as when the seat occupant leans forward.
This would have the effect of distorting the sheet-metal bearing housing halves around the securing screws. At worst the balls might escape from their groove, or the sheet-metal be permanently deformed.
So the design problem becomes one of how to limit tilt-type loads at the lazy susan. I think some type of tilt limit stops outboard of the lazy susan bearing would do the job, such as teflon pads on the lower face, shimmed to such a height that they just contact the upper face when the assembly has say 100 Kg central load.
They are not however rated for any sideways load at all. I think the main problem in your application would be stresses on the bearing cage introduced by off-axis loads and tilt, such as when the seat occupant leans forward.
Hi Geoff,
Great looking mod. If they are not rated for sideways loads, how would they go on a Dob on an EQ platform which tips from -7.5 deg. to +7.5 deg? Would some modification be needed or could they still be used as is? I like this mod as my Dob is sticky in the azimuth direction at the moment, but I would like to build an EQ platform in the future.
A bit off-topic, but you’ve got me thinking – would the lazy Susan be strong/smooth enough to be used as the azimuth rotation on a motorised bino seat, with the full weight of the observer, chair, mount and binos?
Cheers
Dennis
Dennis,
I used the terrible roller bearing from my 12" GS Dob to make my Bino chair. It works terrific and can take LOTS of weight. My son and I stand on it and spin!
You could always use a pair of UC208-108 bearings, has a 40mm hole in the middle and can take over a ton of punishment if not more I have two here with 10mm plate would be able to balance a 40" scope no worries LOL..
Great looking mod. If they are not rated for sideways loads, how would they go on a Dob on an EQ platform which tips from -7.5 deg. to +7.5 deg? Would some modification be needed or could they still be used as is? I like this mod as my Dob is sticky in the azimuth direction at the moment, but I would like to build an EQ platform in the future.
Cheers.
Hi Andrew,
I reckon such a bearing would go OK in this application as any eccentric loading would be negligible compared to Dennis' requirement.
For situations like Dennis' which might involve significant sideways force or eccentric loading, I came across a very appealing and clever variation which uses a combination of 2 opposed lazy susan bearings to cope with forces which would tend to pull the upper (larger) bearing to bits.
Doesn't that diagram look like something familiar?
We should bear in mind that a nearly static load like your application is a different matter to a dynamic load, which would result from a large person (such as myself ) hopping on and off a seat and leaning this way and that. Add a few g's to a static load and it changes the situation quite a bit.
If you are interested in bearings generally as I am, look at
I went down to our local Bunnings on the weekend and found that the only lazy susan they had was one for a TV, in either 10" or 12" sizes. These ones were encased on plastic and sold for around the $30 mark. Are these the ones we're talking about here, or do the ones in the article come as they appear in the photo in article?
I went down to our local Bunnings on the weekend and found that the only lazy susan they had was one for a TV, in either 10" or 12" sizes. These ones were encased on plastic and sold for around the $30 mark. Are these the ones we're talking about here, or do the ones in the article come as they appear in the photo in article?
Cheers
Chris
Hi Chris,
They are encased in stiff plastic, about $27 (too much), and the one I purchased from Bunnings was a Howard Silver brand. When you break it out it is a single unit as it appears in the article.
Hi all..I used a 300mm Howard Silvers bearing for my 10" motorized dob base project..it will take the weight ok..but I had to incorpoate a few extra tiny nylon wheels on outrigger arms plus a central bearing support bolt to stop the sideways movement...
I'm thinking of building a mount plus chair set-up..but I'll use a stub axle and wheel rim from an automotive wreckers for the base..better to be over-engineered than under!
Cheers!
I tried the centre packing and it works a treat. The idea is too relieve pressure on the teflon sliders.Good in theory,but for some it does not work. You need viariable pressure! The easy way is too use as many thin plastic washers as possible, or at least one thin rubber washer between the plastic ones. As a turner i have machined a central bush bearing. It is made in two parts, like T shaped bushes that slip into each other. It is internaly spring loaded. I can use small washers under the spring vary the pressure. The flanges on each bush are screwed too the top and bottom boards. I have not tested this set up yet as I plan too make a complete dob mount from ply instead of the GSO one I have at present. Keep experimenting, when you get it right it makes tracking at high powers a breeze.
My SW dob azimuth mount has typical sticking and jerking problems.
I am not very good at handyman projects.
I have tracked down a lazy susan type bearing (which I reckon I can install) but can't help wondering if the movement in the centre bolt/washers will remain a problem.
Any suggestions for a novice?
Peter
My SW dob azimuth mount has typical sticking and jerking problems.
I have tracked down a lazy susan type bearing (which I reckon I can install) but can't help wondering if the movement in the centre bolt/washers will remain a problem.
Peter
Hi Peter,
It has not been so in my case. I've since fitted the same mod to a 300mm Bintel with success, and it has Argo Navis on it as well.
Think of it this way: with the original teflon pads there is any amount of sideways movement allowed, governed only by the fit of the centre bolt and its metal sleeve. Even if you don't do anything to the centre bolt the situation is actually improved somewhat by the bearing.
The lazy susan bearing has an upper and lower semi-circular track made of pressed sheet metal, with ball bearings between. If not subjected to any appreciable horizontal (sideways) load, this arrangement will always tend to settle into the same alignment under the (mostly) vertical load. So, when panning the telescope around in azimuth, any small amount of misalignment should settle out as soon as you stop. However the bearing ring does have to be installed concentrically around the centre bolt to within a few millimetres, say two.
What this bearing can't handle is eccentric loads, that is, rocking movements. The elevation movement of a Dob is OK because that axis is compliant and does not transmit much rocking-type load to the base, but you can elect to limit such movement anyway between the two halves of the base plate by installing teflon pads outboard of the bearing, of a thickness just less than the thickness of the bearing.
Hope this assists
Cheers
Last edited by GeoffW1; 01-02-2009 at 12:15 PM.
Reason: spelling
Found a 305mm lazy susan/roller bearing at Bunnings --- brand name Prestige and cost about $35. Works a treat. Did away with axis bolt.
Peter
Hi Peter,
Good to hear of your success.
Removing the centre bolt is something I had not thought of, probably because I can't - it has an Argo Navis encoder on it, but please keep us informed on how that further refinement performs for you.
I think i have solved the stiction problem cheap and easy. As i mentioned earlier, you need a system to vary the pressure between the top and bottom boards. Instead of just plastic spacers,a couple of rubber O-rings with plastic shims either side of the O-rings works just great. If you place the first O-ring around the thin tube surrounding the centre bolt, and the second O-ring, of the same thickness but larger around the first, and the thickness of the rings about the same as the space between the boards,experimenting with the number of plastic shims to get the right lift,easing the pressure on the teflon pads. No More Stiction !!!.
I have two here with 10mm plate would be able to balance a 40" scope no worries LOL..
) hopping on and off a seat and leaning this way and that. Add a few g's to a static load and it changes the situation quite a bit.
