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  • Turning end of a scoping device

    Discussion in 'The main mechanical design forum' started by chessblaster, Dec 20, 2012.

    1. chessblaster

      chessblaster Member

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      Hi

      I need some help in designing something which looks as shown in the pic.
      This is for a scoping device where both the tubes attached to the bearing rotate independently.

      I am not able to find a right bearing for this. All the slewing ring bearings are huge in size. But the tubes I need to use are just 1.5 to 2.5 inches in size.

      Can somebody please help me with any alternate design for the same.[​IMG]
       
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    3. mvalenti

      mvalenti Well-Known Member

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    4. chessblaster

      chessblaster Member

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      Thanks mvalenti.

      Actually I dont want to weld the pipes to the bearing. That is the reason I am trying for slewing ring bearings which are not available in smaller sizes. Can you please help with any other alternative.

      Are there any thin section bearings available with holes to fit bolts ? Please point me to any such bearing.
       
    5. AndrewNew

      AndrewNew Well-Known Member

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      Why do you need to bolt the bearings to the tubes? Can you put a step on the end of the smaller tube and a pocket in the larger tube and set the bearing using a retaining compound (Loctite have a range)? Depending on the loading and kinematic conditions you might get away with a deep-groove ball bearing or other bearing with thrust-transmitting capability.
       
    6. chessblaster

      chessblaster Member

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      Thanks Andrew.
      Actually, I thought bolting the tubes would be the easiest as the pipes are thick enough pvc ones and the pipes are held onto bearing. I will check the retaining compound idea as you suggested.

      I thought of a pipe over pipe and bearing in-between them idea. But not sure how to place the bearing in between the larger and smaller pipes.

      Thanks
      Suresh.
       
    7. AndrewNew

      AndrewNew Well-Known Member

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      It could work, but as you've found it reduces your choice of bearing type dramatically. And I wouldn't even bother trying to drill your own holes in a bearing race, even if you find one of appropriate size, they are extremely hard.

      There are many ways of retaining a bearing in a housing or on a shaft. Clamps, grub screws, interference fits to name but a few. Modern retaining compounds work very well and save you all sorts of troubles, not least that you don't have to machine your housing/shaft to very tight tolerances, as you do if you want an interference fit. You do have to be a bit more careful of alignment during fitting though.

      Since you are using PVC pipe I suspect your loads are fairly modest. The interference fit option is probably out since the PVC will creep and not maintain the interference in the long term. I'd be tempted to try a retaining compound - you'd just need to make sure the one you chose is compatible with PVC and that you have the appropriate clearance between the bearing races and the shaft and housing to allow the compound into the joint. The manufacturer's data sheet for the retaining compound will contain this information.
       

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