CNC 60cm x 90cm Ball screw dia size?


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Thread: CNC 60cm x 90cm Ball screw dia size?

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    Default CNC 60cm x 90cm Ball screw dia size?

    Plan to build CNC working area is 60cm x 90cm. Z distance is 10cm.
    For robot, uav, drone, rov, small wood work.
    Work with wood, acrylic, aluminium.
    Plan for 10mm pitch. BK,BF support.

    What should be ball screw dia size?
    Any other comment is appreciate.

    Similar Threads:
    Last edited by nquantum; 12-06-2019 at 08:25 AM.


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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    Hi,
    the diameter of the screw determines the stiffness/rigidity of it, obviously the larger the better from the point of view of strength.

    A more subtle effective minimum diameter is the maximum rotational speed.

    The most comprehensive deign guide I have seen on the subject comes from the NSK Precision Components catalogue:
    http://www.nsk.com/common/data/ctrgPdf/e3162h.pdf

    Section B-2-3

    The important parameters are the max unsupported length, that is the max distance between the ball nut and either of the support units, and the nature
    of the support units, ie fixed, floating etc.



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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    Thank for reply seem it more detail in those catalog. Will try to study it. Initially I plan to use 20mm diameter.



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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    Hi,
    the design guide suggests that the max permissible speed for one fixed, one floating support and 900mm free length at 20mm diameter
    is about 3000rpm. At 10mm pitch that is 30m/min rapids, that's pretty quick!

    Craig



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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    Quote Originally Posted by joeavaerage View Post
    Hi,
    the design guide suggests that the max permissible speed for one fixed, one floating support and 900mm free length at 20mm diameter
    is about 3000rpm. At 10mm pitch that is 30m/min rapids, that's pretty quick!

    Craig
    I capture to make sure I understand your. Start with 900mm free lenght then find the cut at 20mm diameter then down to fine permissible speed at fix-simple support. That is about 3000rpm. That correct?

    CNC 60cm x 90cm Ball screw dia size?-1-jpg



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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    Hi,
    yes, that how I read it also.

    I would regard this as a maximum and your design and construction must be good to achieve it.

    For instance if you have a significant misalignment between the motor and the ballscrew the flex coupler will exert a small cyclic force
    as it flexes, once per revolution. That would be a vibration which could start the ballscrew whipping. Likewise any misalignment of the mounting
    of the ballnut would cause a force which would promote whipping. In short any small error is construction could badly compromise the stability of the
    screw in rotation.

    Having said that....if your construction is good, and no doubt that's exactly what you'll be trying to do, and likely achieve in good degree, then I would
    expect you to be able to spin 20mm screws at close to 3000rpm without whipping.

    Craig



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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    Thank for verify my read. So base on that. if I use:
    16mm I can have maximum of about 2500rpm , 25m/min
    10mm I can have maximum of about 1000rpm , 10m/min

    Aside from my construction good or not.
    Then I think I can lower from 20mm dia to 16mm still good condition.
    Am I miss something?



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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    Hi,
    that's what the design graph indicates, although I find it hard to believe that you could spin a 10mm ballscrew (900mm unsupported) at 1000rpm WITHOUT it
    whipping.

    Assuming that whatever screw you choose is adequately stable at high rotational speeds then all then really need be considered is stiffness ie
    static and dynamic load.

    I am building a new CNC mill with cast iron beds and frame, intended for high accuracy milling of steel and stainless steel. For my build I have found and bought
    some 32mm diameter C5 ground ballscrews. Note that the rigidity is quoted as 1110 N/um.

    These screws are supported at both ends by fixed bearings and are only 700mm overall long. They could, in theory, be spun at very high rpm. My selection was not
    made for that reason but rather the stiffness....unless a ballscrew is very stiff it will be hopelessly inaccurate.

    I would recommend the largest, stiffest, most accurate ballscrews you can afford. The ballscrews are often the limiting feature of any CNC machine. Limitation
    of accuracy/repeatability by virtue of the ballscrew is closely followed by the linear rails or guides followed by the frame of the machine. There is no such thing
    as 'too rigid' but 'not rigid enough' is a very VERY VERY common complaint.

    Craig

    Attached Thumbnails Attached Thumbnails CNC 60cm x 90cm Ball screw dia size?-ballscrew-jpg   CNC 60cm x 90cm Ball screw dia size?-bnbf3205-png  


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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    Quote Originally Posted by joeavaerage View Post
    Hi,
    that's what the design graph indicates, although I find it hard to believe that you could spin a 10mm ballscrew (900mm unsupported) at 1000rpm WITHOUT it
    whipping.

    Assuming that whatever screw you choose is adequately stable at high rotational speeds then all then really need be considered is stiffness ie
    static and dynamic load.

    I am building a new CNC mill with cast iron beds and frame, intended for high accuracy milling of steel and stainless steel. For my build I have found and bought
    some 32mm diameter C5 ground ballscrews. Note that the rigidity is quoted as 1110 N/um.

    These screws are supported at both ends by fixed bearings and are only 700mm overall long. They could, in theory, be spun at very high rpm. My selection was not
    made for that reason but rather the stiffness....unless a ballscrew is very stiff it will be hopelessly inaccurate.

    I would recommend the largest, stiffest, most accurate ballscrews you can afford. The ballscrews are often the limiting feature of any CNC machine. Limitation
    of accuracy/repeatability by virtue of the ballscrew is closely followed by the linear rails or guides followed by the frame of the machine. There is no such thing
    as 'too rigid' but 'not rigid enough' is a very VERY VERY common complaint.

    Craig
    I see you use big screws 32mm! Because you want work with steel and stainless steel.
    For me I plan to work for wood acrylic aluminium. I see some spec of screws from internet. Although I not know it will enough. So I will stick to 20mm seem to be safe.

    CNC 60cm x 90cm Ball screw dia size?-ball-screw-ofu-dfu-tbi-supply-jpg



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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    For this machine I plan to use Nema23 Torque 3 N-m. good enough? Since this is not production use. More for research and hobby and I've read somewhere.

    The decision between NEMA 23 and NEMA 34 motors is primarily a decision about productivity -- NEMA 34 motors can remove material at a higher rate using higher feed rates and deeper cut depths. ...
    Generally, if you are using a machine for regular production work, higher power NEMA 34 motors will provide a fast return on investment. However, if you are primarily doing small production runs or prototyping work, NEMA 23 motors will likely be sufficient.
    So for save budget, space, weight then I go for Nema23 Torque 3 N-m. instead NEMA34 8.7 N-m. good?



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    Default

    Quote Originally Posted by nquantum View Post
    For this machine I plan to use Nema23 Torque 3 N-m. good enough? Since this is not production use. More for research and hobby and I've read somewhere.



    So for save budget, space, weight then I go for Nema23 Torque 3 N-m. instead NEMA34 8.7 N-m. good?
    Some comment please



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    Default Re: CNC 60cm x 90cm Ball screw dia size?

    Hi,
    the trick with steppers is to understand that they all lose torque the faster they go. Low inductance steppers are best, they retain more of their torque at 1000 rpm
    than high inductance steppers.

    It may be that a low inductance (1mH) 23 size stepper of 500 oz.in will have more torque at 1000 rpm than a 34 size 1000 oz.in but 8mH inductance.

    If you are of the opinion that 3Nm is enough for your machine then by all means save some money and get them rather than the bigger 8.7Nm ones but
    make sure the inductance is between 1 and 2 mH, closer to 1mH is preferred, otherwise your machine will stall at any above slow speed.

    I'm using Delta 750W servos, they have only 2.4Nm (continuous) but retain that torque up to 3000 rpm. Servos have a very good overload capacity that steppers
    don't have, my servos will deliver 7.2Nm as a temporary overload. They are powerful and fast.....not cheap....approx. $500USD each for servo and drive.

    Craig



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CNC 60cm x 90cm Ball screw dia size?

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CNC 60cm x 90cm Ball screw dia size?