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Thread: Fusing a nut to a lever (need ideas)

  1. #1
    Associate Engineer
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    Fusing a nut to a lever (need ideas)

    Hi everyone,

    I'm new here so sorry if this breaks any rules or causes any trouble. I hope this is the right forum to ask mechanical design questions while prototyping because I constantly running into issues that I'm sure there's a part for but never know what exactly I'm looking for.

    But I was hoping to get some ideas for a prototype I'm helping build. We'd like to fuse a square nut to a small lever arm from a linear potentiometer, so my first thought was simply some JB weld and call it a day, but my partner would like to look at more robust solutions.

    So here's what the system might look like if we went with the glue:
    SquarenutJBweld.PNG

    But then I thought, maybe we could drill holes through the lever and semi-circle holes through the square nut like so:
    SquarenutMilled.PNG

    And then simply add nuts and bolts:
    SquarenutBolted.PNG

    And looking at it now, it seems I might need a top plate that can clamp the whole system together.

    My question for you all, is there a simpler way of achieving this? Perhaps a different type of nut that could make this setup easier? We're going for quick assembly here, and both of my solutions would be time-consuming (especially aligning and milling those holes). So any ideas?

    Thanks in advance

  2. #2
    Project Engineer
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    Can you curl the end of the lever into a loop that the threaded rod can pass through? (with a nut on each side)

  3. #3
    Administrator Kelly Bramble's Avatar
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    Electric current welding - if you have the equipment. Same as spot welding.
    Tell me and I forget. Teach me and I remember. Involve me and I learn.

  4. #4
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    Depending upon the strength required, torch or oven brazing may be another option.

  5. #5
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    I would question why you think a nut is a good idea there. As the threaded fastener you are putting in there moves around the potentiometer, now you have a few mechanical problems -

    1) if the male thread doesn't rotate just in sync with everything else, that will pull the nut in or push it out as you change the angle, putting axial stress on the potentiometer (generally a bad thing). To what degree depends on the pitch of the thread and what angle of motion you're using, but an unthreaded hole would eliminate that stress
    2) This assumes that you have very good control of the motions of the male thread, that it moves only in a perfect circle, with the same radius as the nut to the axis of the pot, and that the axis of the pot and axis of the input are perfectly collinear, and that the input thread itself doesn't ever try to point in a different direction, as any of those would again stress the pot.

    If you could put a slot in the arm of the pot or have it forked with the input as a smooth pin, or change the input to a fork that is allowed to rotate, that would be much more forgiving of imperfect alignment. That will also add some hysteresis to the system, how much depends on how closely the parts are fit.

    Harry R. Burger
    BSME, CSWP

  6. #6
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    Thanks for the replies everyone, I'm sorry for the delay getting back.

    Let's see,

    Can you curl the end of the lever into a loop that the threaded rod can pass through? (with a nut on each side)
    Unfortunately, we're trying to work around the geometry of the lever as is. In order to have a very repeatable design. But thanks for the ideas!

    Depending upon the strength required, torch or oven brazing may be another option
    Honestly, we're just looking to beat JB weld which will theoretically hold ~85 lbs in shear. So perhaps a braise joint would be a good option here.

    I would question why you think a nut is a good idea there.
    I think I understand your concern here. But the nut is here because we want both translation and rotation of a threaded rod. I couldn't think of any other type of joint that would allow our potentiometer to capture the translation while still allowing for a controlled rotation. But I believe that so long as everything is aligned well, and the threads are somewhat relaxed fit, the potentiometer should be able to survive the threading action.

    Thanks everyone for the ideas, please let me know if anything else comes to mind or if you disagree with my replies.

  7. #7
    Project Engineer
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    looped lever


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