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Gantry and Bearings

Discussion in 'CNC Mills/Routers' started by Project Hopeless, Feb 12, 2019.

  1. Project Hopeless

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    As a first build I'm looking at using plywood and SBR linear bearings. A typical gantry might look like so...
    upload_2019-2-12_20-53-34.jpeg

    I'm curious, is there anything wrong building the gantry like this...

    upload_2019-2-12_20-54-22.jpeg

    What I'm wondering about is the twist generated by the router hanging far off the gantry/beam. My though is the closer to the beam the less torque/twist.

    What do you think?
     
  2. GrayUK

    GrayUK Openbuilds Team Elder
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    If you are making a fixed gantry and moving bed machine, you can remove the chance of twist by using two beams.
    Put one linear rail on each and your screw wherever suits you.
     
  3. SugarJ

    SugarJ Veteran
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    Can I make a suggestion? Find a piece of steel HSS C-channel or tubing to attach your SBR rail to instead of trying to make a stable box beam out of plywood. The torque put on your gantry is a lot more than you'd expect. I watch my Ox gantry flex while it's cutting aluminum. Visit a local steel fabricator, they've probably got a scrap piece they'd let go cheaply for cash.
     
  4. Gary Caruso

    Gary Caruso OpenBuilds Team
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    Hi PH,
    Problem with top and bottom is getting the rails parallel will be much harder if not impossible.
    Cheers
    Gary
     
  5. Project Hopeless

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    This build is intended for cutting wood and plastics. If I can mill aluminum great, its not a must. I think wood is going to be an easier build for me at this point.

    That beam pictured is simplified. It will more closely resemble a torsion box (internal bracing) when done.

    I wondered about that. That is what concerns me, keeping everything square and parallel.
     
  6. Rick 2.0

    Rick 2.0 OpenBuilds Team
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  7. Project Hopeless

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    I see your point. My first though was through bolts, flat washers , and possibly hardwood backer blocks.

    I did come across hybrid material builds like so;

    The Growler

    https://photobucket.com/gallery/user/BungalowFilms/media/bWVkaWFJZDoyMjUxNTc1OQ==/?ref=

    Q: threading into the face of an extrusion, Is there very much holding power? Doesn't seem like there would be enough threads, wall thickness is too thin. In these link that looks like what the builders did.
     

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