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Using a bearing to replace a spring?

  1. Jan 26, 2015 #1
    I am working on a project that uses a box design with a base. The base has two through holes on the the outer edges that will be used to slide up and down with in the box. The box will support two guide rods where the base can slide up and down.

    My intention was to use springs so that as the box is loaded the base gradually lowers. The travel is about 16'' which is a rather long spring and also takes up considerable space when compressed. Does anyone know some sort of alternative to the spring?

    My initial thought was some sort of bearing in the base that would only slide when a certain amount of force is applied. So far I am unable to find such a bearing. Let me know of any thoughts or ideas?
     
  2. jcsd
  3. Jan 26, 2015 #2

    Quantum Defect

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    It is hard to picture what you have in mind. Linear bearings are very nice for allowing horizontal travel.
    http://www.thomsonlinear.com/website/com/eng/products/linear_bearings_and_guides.php

    ... not sure if you can find something with an internal spring...
     
  4. Jan 26, 2015 #3
    I am looking for linear bearing, I think a thrust bearing, that would only move after a certain amount of static force is applied to it. That way as the box is loaded the operator just has to push on the top most part and the platform will lower as long as the operate is pushing, until the platform bottoms out. Below is an early design the black part is the platform that will slide up and down, the springs can be seen on the outer edge. However when the springs are compressed they will take up a significant amount of space. Also in the middle of the springs is a guide rod that will support the spring and work with the platform to move only up and down.
    upload_2015-1-26_16-43-57.png
     
  5. Jan 26, 2015 #4

    billy_joule

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    You don't need (expensive) linear bearings, and you definitely don't need (also expensive) thrust bearings. Bearings are to reduce friction, not "only slide when a certain amount of force is applied", that is the opposite of what bearings are supposed to do!

    What exactly is the purpose of your device? If you can explain it's function well we can provide better advice. Does it need to self reset? A counterweight, pulley & cable is an alternative to springs.
     
  6. Jan 27, 2015 #5
    Perhaps a cable operated counterweight, such as used with elevators?
     
  7. Jan 27, 2015 #6
    You can use gas springs, Once the load is reached the edges will slide down in the box. But the space used is also big.
     
  8. Feb 6, 2015 #7

    jh0

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    Gas springs, compression and tension coil springs, even rubber bands, all are going to use up a big space. Maybe some mainspring (spiral spring like in mechanical watches) can be pretty compact, but it will be more complicated: you will need to connect the mainspring to a cylinder with a some coiled cable and maybe some pulleys also.
    It comes to my mind maybe it's possible to use a tool balancer like these:
    http://www.grainger.com/category/tool-balancers/fastening-tools-and-accessories/power-tools/ecatalog/N-p0f [Broken]
     
    Last edited by a moderator: May 7, 2017
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