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  1. #21
    Quote Originally Posted by Robin Hewitt View Post
    But the diagram doesn't show the rails being screwed to the bed and the blocks being screwed to the gantry.

    The nut should be under the gantry and the screw moving with the bed.

    That puts the linear bearings permanently underneath the cutting head.

    Looks a bit odd, but if you draw it you will see enormous benefits.
    Hi Robin,
    Yes, I totally get what you are saying. Putting the bearings on the bed and the rails on the moving part makes good sense but it is maximising stiffness in the vertical Z direction. It is similar to the debate around conventional Z axis where it is often better to put the rail on the moving part for the same reason.

    However, the bracing on the tower is primarily to address stiffness in the X direction. I've re-drawn the sketch to show the moving rails and FIXED bearings but the forcing (for X direction) is still the same and suggests bracing of the tower is beneficial.

    X cutting:
    Click image for larger version. 

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    There is also some Z direction stiffness from the bracing due to moment created by the offset of the tool from the tower in X which is independent of the rail / bearing arrangement.

    Z cutting/ plunging:
    Click image for larger version. 

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    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  2. #22
    Quote Originally Posted by JAZZCNC View Post
    please stop calling it the gantry it's the base Frame and I'm easily confuddllledd. .
    With both methods the rails have a length equal to the table travel plus the overall width of the bearing block assembly.

    In this topsy turvey arrangement I am advocating the block assembly width is tiny in comparison, so the rails are short.

    If you could bolt the "base Frame" to a workbench this could look ultra neat.

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