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Allowable deflection?

Discussion in 'CNC Mills/Routers' started by drxlcarfreak, Jun 12, 2017.

  1. drxlcarfreak

    drxlcarfreak Journeyman
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    Following up from this great resource (How to calculate V-Slot® deflection) to calculate deflection, what is a good deflection to shoot for? It looks like assuming a 10kg load, the 750mm C beam router (C-Beam Machine XLarge) is calculating out to about 0.03mm of sag in the middle of the space. Actually a related question, the link is saying 0.140mm, which is using the horizontal moment of inertia, not the vertical which would be from the weight of the Z axis and router. Is this assuming a 10kg cutting force?

    Assuming this is correct, would a good design aim to be under 0.14mm of deflection in both directions?

    The reason I ask is I have been working on a 850mm gantry design, as a good middle ground between rigidty/price/cutting width (plus it has successfully been done before on rigid machines), with the intentions to get up and running and then expand to a 1500mm gantry so I can slide full sheets of MDF through eventually, but am questioning myself if I should just jump into the design of a 1500mm wide gantry from the get go so that I wont have to buy parts, and un/reassemble multiple times.

    As usual thanks for all the input guys!
     
  2. drxlcarfreak

    drxlcarfreak Journeyman
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    A possible newbie question... If aiming for a machine with repeatability of say just under 0.1mm, how does that work on a machine that deflects slightly more than that?
     

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