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New machine, question on lead screw tension

Discussion in 'CNC Mills/Routers' started by Retrosmith, Nov 16, 2017.

  1. Retrosmith

    Retrosmith Journeyman
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    I'm finishing up the mechanical portion of a new 1000mm x 1000mm machine and have some concerns about screw deflection (whip). In Mark's video he advises a slight compression preload on the screw, but I've read that this can make screw whip worse.

    I have ample room on this machine to sacrifice a couple of inches, so I was curious if there would be any advantage to putting a slight tensile load on the screw? My thought is to cut a couple of inches off of the C-beam to allow access to the extra length of the screw out the end plate that doesn't have the motor mounted to it, then once the bearings are well seated in the plates to put a brass Acme nut on the screw outside the plate and tighten it down before tightening the lock collar.

    Can anyone with more mechanical knowledge than I tell me if this would have any effect on keeping the screw in line?
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
    Staff Member Moderator Builder

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    You might watch the SMW3D video on tensioning the screws. You shouldn't need to shave more than 1/2" off the C-Beams to make it work. Simply reverse the end plates and drop F8-16M bearings in the bearing recess. Lock collar on the free end and the flex coupler on the other. You'll either need to add a few shims under the coupler or order some shorter stand-offs for the motor as the separation distance becomes a little more critical.
     
  3. Retrosmith

    Retrosmith Journeyman
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    Interesting, thanks!
     
  4. ChadRat6458

    ChadRat6458 Journeyman
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    That is cool. I have my basic frame put together. I don't want to take it apart. I will get some more lock collars. I use the new collars to put some tension on like in the video. I will probably need to loosen the old collars then tighten them back up after the tension is set. Thanks.
     

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