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Thread: Wrong bearing choice or need for lubrication?

  1. #1
    Associate Engineer
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    Wrong bearing choice or need for lubrication?

    Hi everyone !

    I ordered two bearing units to guide an axis that will be driven by two torsion springs (see 'mecanisme' picture below). The aim of this assembly is basically to create a 'catapult' that can shoot downwards (see 'global_rendu' picture). As you could expect from such a basic system the torque is pretty small as well as the rotation speed (from 0 to 15 rad/s at the end) of the whole system.

    Now the two NTN M-UCP 204 D1 bearing units (technical sheet enclosed) I ordered seem to slow down very much the rotation of the axis having a huge impact on the final speed of my projectile.

    I know about the design requirements to make the bearings resist to different kind of loadings but I had no idea about the slow-down of the units. Do you think I ordered a units that isn't suited for my application (small rotational speed) or that I should just add lubricant or maybe there is just a screw that need to be loosen?

    Cheers from Belgium.
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    Last edited by bobaudinet; 05-20-2017 at 06:26 AM.

  2. #2
    Administrator Kelly Bramble's Avatar
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    Driving force not large enough, improper bearing installation, oversized bearings for the application, high friction bearing chosen, etc.

    Re-assess your bearing - driving force application.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  3. #3
    Technical Fellow jboggs's Avatar
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    I see no need to use rolling element bearings in this application. The loading is very light. I would have chosen plane bearings like those available from Pacific Bearing (PBC) or Igus. They have very low internal friction and lubrication is not an issue.

  4. #4
    Associate Engineer
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    It was the very first time I purchased bearings and thought all bearing could do the job as my load was really small as you noted. Moreover, the choice of the bearing was guided by a sales assistant and one of the main requirement was that it had to be available in the stock of my local supplier. This explains why it's undoubtedly oversized.

    That being said, and considering I already have those and might not be able to return it, I was thinking about removing the grease and seals then lubricating it with oils to lower the friction. Do you think that this would be a workable solution?

  5. #5
    Technical Fellow jboggs's Avatar
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    Maybe. Until some grit gets in there. Try it and see. The bearings I mentioned are available on line in many places. Probably the most widely used in McMaster.com.

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