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Big Sphinx questions

Discussion in 'CNC Mills/Routers' started by Coyote_ar, Aug 27, 2017.

  1. Coyote_ar

    Coyote_ar New
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    Hi everyone, so im thinking on building a big sphinx. I love the design with the c-beam actuators. I want to build a big machine, but im concerned that it may start flexing when milling aluminium. How big can you go before c-beam starts flexing?

    I was thinking 1500mm length c-beams for both X and Y axis (not sure whats the real working area). Is this something ok for aluminium?

    Any other tip regarding building a big machine?

    Your advice is really appreciated, regards.
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    That's not the right question. Any member, no matter how long or how short the span and no matter how great the forces acting upon it are, will flex. And the extent of the flexure will be anywhere from imperceptible to totally unusable based on the combination of the length and the load. There is no point where it "starts" to happen other than at the very beginning.

    The question should be "how far can you span before flexure makes the system unusable?" And the answer to that would truly depend on the the weight of the spindle, the size and speed of the bit, the rate of motion and what you consider the acceptable tolerances to be. So as you can see, there is no simple answer to the question. But at 1500mm, you're not gonna get even close to any acceptable level of precision cutting aluminum. Cutting aluminum requires rigidity and the larger the machine gets the less rigidity it has. If you wish to cut aluminum you really need to think through your parameters and figure out what is the smallest machine you can get away with as that will be the best machine you can build for the job.
     
  3. Coyote_ar

    Coyote_ar New
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    Hi Rick, thanks for your response. I understand what you are saying.

    Please correct me if im wrong, but the axis more susceptible to flex a lot is the X axis. Correct? So if i wanted to reduce the size of the machine to improve its rigidity, reducing it on the X width, would provide more gains than doing it on the Y axis.

    In that case lowering the width of the machine, say 1000mm length but only 500mm wide. would result in a more rigid machine.

    Is this correct?
     
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Yes, that is correct. Additional ways to make the system more rigid include bracing the Y-axis rails as frequently as possible and keeping the X-axis beam as low and close to the Y-axis rails as you can get away with.
     

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