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alantastic
Starting Member

2 Posts

Posted - 29 Jun 2011 :  15:31:36  Show Profile  Visit alantastic's Homepage  Reply with Quote
Hello all,

I'm trying to build an art project that involves a static center platform about 11 inches in diameter, with a rotating outer disc 1 inch wide. The idea is the outer disc will spin at around 60rpm as silently as possible. Here is a diagram that describes the problem:



Trouble is, I can't for the life of me figure out how the mechanics of this should work. I can build the electronics and the servo motor etc, but bearings are beyond me. I started by looking at lazy susan bearings like this one:



…but the problem is that these bearing are quite loud. After a bit of thinking, I wonder if this is because there is that much more "travel" of the surfaces on one another and that I should consider a small bearing in the center, with shafts radiating out (like spokes of a wheel).

The problem is that I don't understand how to connect these two surfaces to a central bearing. I have looked at bearing housings and bearing units, but all of them seem to be geared towards a fixed outer housing, and a rotating shaft in the center. What I want is the opposite. So if I have a small bearing and a static shaft, how do I connect this rig to the outer portion of the bearing? And if I do that, will the bearing itself be able to handle the weight of the outer platter?

I'd love some help, specifically that points to places that I could actually purchase a solution. I don't mind spending some money on it, or having it custom made, even, but I don't really know many online providers of these services (other than RS Components).

Many thanks to anyone that can shed some light on this.

Cheers,

Alan

slurp
Geek!

United Kingdom
497 Posts

Posted - 29 Jun 2011 :  17:55:45  Show Profile  Visit slurp's Homepage  Send slurp a Yahoo! Message  Reply with Quote
The noise comes from how precisely the bearing is manufactured, it may be that you can adjust the construction to stop any loose rattling that's giving rise to the noise.

There will be a variety of industrial bearings available that will be much quieter, it's common to see these with integral gears for driving directly. Your looking at something that's very similar to a crane slue but on a smaller scale.

Have a google for slewing rings and slewing bearings.

Best regards,
Colin
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alantastic
Starting Member

2 Posts

Posted - 01 Jul 2011 :  08:07:57  Show Profile  Visit alantastic's Homepage  Reply with Quote
Thanks Alan,

I did actually look at slewing rings quite a bit on the internet, but unfortunately nobody seems to make them on a small scale, and under about £300. Perhaps I'm not looking in the right place?

I was thinking that one solution could be to use a flange housing like this one:



... which would bolted on to the outer plate. Then the center mountain would be attached to the shaft itself. The problem is, how would I attach the mountain to the shaft? And how would I stop the outer plate from sliding down the shaft?

I'd really appreciate it if you could point me in the direction of some resources to buy these things. Is there a place that you robot gurus use in the UK?

Cheers,

Alan
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slurp
Geek!

United Kingdom
497 Posts

Posted - 01 Jul 2011 :  16:20:48  Show Profile  Visit slurp's Homepage  Send slurp a Yahoo! Message  Reply with Quote
It's been quite some time since I needed a slew ring and then it was something much bigger. I when to Rollix directly but I'd suggest asking your local Brammer. Google might be good but you'll have a bit of digging to get there. HPC Gears or OnDrives might be able to help too.

If I wanted to hold the position of that bearing I'd used either a stepped shaft or a circlip. The circlip would probably be easiest but still needs machining. There's standard tables to show what sort of load they can carry.

I'd be looking for something under the mountain to clamp the shaft, I don't know how accessible you need to be.

Best regards,
Colin
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Bob
Serious Geek!

United Kingdom
1263 Posts

Posted - 09 Jul 2011 :  07:39:41  Show Profile  Reply with Quote
Hi Alan

You might consider a nylon track with a grove and three ball races supporting the rotating part.





If you inclined the working surface of the nylon track (ie make it conical) the track should self centre. I think the hard steel bearing outers would run silently on the nylon surface.

Just an idea

Bob
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