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Choose the best rail width

Discussion in 'General Talk' started by Hexag, Oct 18, 2014.

  1. Hexag

    Hexag Well-Known
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    Hi everyone !

    Untill now, in the forum, I've never seen anything about how I can choose the best V-Slot rail width (20mm, 40mm, 60mm or 80mm) for a particular situation. So, in that pupose, I just want to start a new discussion about this specific subject.

    Any contribution would be appreciated ;).
     
  2. Rob Taylor

    Rob Taylor Veteran
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    Two reasons to consider different width rails, depending on the orientation of your extrusion. If it's vertically mounted, running horizontally, the width of the extrusion is now the height- and thus providing stiffness to brace against the distortion of gravity. If you have a heavy router running on a single x-axis extrusion, for example, you'd probably end up using 2080 extrusion so that the whole gantry doesn't bow down when the router's in the middle.

    The other reason applies to this same scenario as well, and that's torque, or rotational inertia, or twisting stiffness. If you have wheels running at each side of a V-slot extrusion (or top and bottom in the above example) then the further apart the wheels are, the more stabilising torque they apply to one another (because Tau = F.d). The torsional rigidity (twisting stiffness) of the extrusion is also maximised when it's wider, because the material itself is providing its own heightened moment of inertia due again to its width.

    Does that make sense? I feel like I've misplaced an engineering definition in there somewhere. But that's the general idea, anyway. The reasons to choose different smaller ones aren't based on maximal physical properties, but other engineering concerns like size or cost constraints, or weight and momentum of moving parts, etc.
     
  3. Hexag

    Hexag Well-Known
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    Thanks for your answer Rob :).

    So, for a 3D printer, 2020 or 2040 extrusions would be enough, with an extruder weight of about 0.5kg ?
     
  4. Rob Taylor

    Rob Taylor Veteran
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    I'd probably have the extruder on vertically-oriented 2040 and the rest of the machine just 2020, yeah. 3D printers are definitely the cheapest and easiest BOMs.
     
  5. Hexag

    Hexag Well-Known
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    Ok ! Thanks for your help :).
     

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