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IndustryArena Forum > Mechanical Engineering > Mechanical Calculations/Engineering Design > Do I need linear rail next to ball screw on the vertical axis?
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  1. #1
    Join Date
    Jun 2015
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    Do I need linear rail next to ball screw on the vertical axis?

    Hello, I am considering to build a machine with one ball screw on the left and the other ball screw on the right to generate vertical motion. Is it necessary/highly recommended to add an additional linear rail or two next to each ball screw? Is one linear rail next to a ball screw on each side already sufficient?

  2. #2
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    Jul 2018
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    Re: Do I need linear rail next to ball screw on the vertical axis?

    Hi Laser if the rail is a square type then twin rails are not required. Peter

  3. #3
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    Jun 2015
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    Re: Do I need linear rail next to ball screw on the vertical axis?

    Quote Originally Posted by peteeng View Post
    Hi Laser if the rail is a square type then twin rails are not required. Peter
    Hi Peter, what is a square type rail? I am considering HGR20 with HGH20CA.

  4. #4
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    Re: Do I need linear rail next to ball screw on the vertical axis?

    Hi Laser- HGR is round rail. Round rail needs two rails because the car can rotate on the rail. Square rail supports moments, so the car stays flat. In some cases you only need one rail with a square rail. Publish a sketch of what you want to do. Sounds like your building a laser and want the Z axis to go up and down? Peter

  5. #5
    Join Date
    Jan 2008
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    1523

    Re: Do I need linear rail next to ball screw on the vertical axis?

    You need to provide a picture / model.

    It sounds like you are asking about 2 rails on each side? 4 rails for one axis? It is very rare that more than 2 rails per axis is beneficial

    HGR is square / profile rail (not round rail)
    7xCNC.com - CNC info for the minilathe (7x10, 7x12, 7x14, 7x16)

  6. #6
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    Re: Do I need linear rail next to ball screw on the vertical axis?

    Sorry - Yes SBR is round HGR is square - Peter

  7. #7
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    Re: Do I need linear rail next to ball screw on the vertical axis?

    Quote Originally Posted by pippin88 View Post
    You need to provide a picture / model.

    It sounds like you are asking about 2 rails on each side? 4 rails for one axis? It is very rare that more than 2 rails per axis is beneficial

    HGR is square / profile rail (not round rail)

    I am at the earliest design stage. I have seen various configurations. I am considering three configurations:

    1. On each side, one ball screw with a linear rail next to it
    2. On each side, two linear rails with one ball screw in between

    Thanks for clarifying that HGR is square. I got confused when I read that it is round.

  8. #8
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    Re: Do I need linear rail next to ball screw on the vertical axis?

    Hi Laser - A sketch is worth a 1000 words and you mentioned 3 but gave 2 concepts? Peter

  9. #9
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    16

    Re: Do I need linear rail next to ball screw on the vertical axis?

    Quote Originally Posted by peteeng View Post
    Hi Laser - A sketch is worth a 1000 words and you mentioned 3 but gave 2 concepts? Peter
    As shown in the illustration, there are two power screws. One on the left and the other on the right of the machine.
    I imagine that the stretching beam connects the left and the right power screws. So, it "should?" move up and down parallel to the desk with no tilting in any orientation. Is there any problem with such design?

    I have seen some people putting one or two linear rails (be they SRB or HRG) next to each power screw like some of popular 3D printers. Is it much better to do it like that?

    https://imgur.com/a/LFeDUs4

  10. #10
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    Re: Do I need linear rail next to ball screw on the vertical axis?

    Hi Laser - What you are describing is a universal testing machine. But they usually test in the same space (tension or compression) They use two power screws or ballscrews to move the cross head up and down. The limiting factor is buckling of the screw so its usually large in diameter. So you need to minimise the length of the screw and maximise its diameter. What max load do you intend to apply and what length do you need for compression? Peter

    Universal testing machine - Wikipedia

    In regard to using one or two rails on the columns this comes down to the stability required. In a tension test stability is automatic so one is fine. In compression the stability required comes down to the test load vs the frame stability and the cross head geometry. One large rail or two small rails comes down to cost and design.

  11. #11
    Join Date
    Jun 2015
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    16

    Re: Do I need linear rail next to ball screw on the vertical axis?

    Quote Originally Posted by peteeng View Post
    Hi Laser - What you are describing is a universal testing machine. But they usually test in the same space (tension or compression) They use two power screws or ballscrews to move the cross head up and down. The limiting factor is buckling of the screw so its usually large in diameter. So you need to minimise the length of the screw and maximise its diameter. What max load do you intend to apply and what length do you need for compression? Peter

    Universal testing machine - Wikipedia

    In regard to using one or two rails on the columns this comes down to the stability required. In a tension test stability is automatic so one is fine. In compression the stability required comes down to the test load vs the frame stability and the cross head geometry. One large rail or two small rails comes down to cost and design.
    The one I got is SFU1605 500mm. The max load maybe about 5KN. My main concern right now is whether or not to add at least one rail on each side as doing so increases the cost. What could go wrong if I don't use any rail and just make the cross head to move up and down in compression tests using only a pair of SFU1605? How likely will that problem happen?

  12. #12
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    Jul 2018
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    Re: Do I need linear rail next to ball screw on the vertical axis?

    Hi Laser - Murphy is always lurking around in machine design and things do go wrong! But here are the numbers. 1) The screw is unlikely to buckle at 5kN especially since the load is shared between two screws (screw is in compression in tension test). The screws buckle at about 15kN each but load sharing is rarely perfect so machines would be designed not at equal share. But I think your clear here. (screw is in tension in compression test so is stable) 2) To generate 5kN you need 2.2Nm per screw. Thats achievable with small motors so seems Ok to move fwd without using rails. You can use 2 separate motors that are synced eg steppers or use one motor and belts to each screw. So you can use an induction motor or DC motor then and a load cell to measure load. You will need a load cell in all cases. Peter

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