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    I've been thinking about how to attach bearings and a timing pulley to a ballnut such that it can be rotated with a stepper motor, instead of rotating the screw.

    I've already done this on my router with an M20 screw since the long X-axis means that screw whip and inertia would have limited the speed significantly:

    Click image for larger version. 

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    This is, I think, the most promising design I've come up with for rotating a ballnut. The chosen ballnut is the standard RM2510 ballnut from linearmotionbearings eBay seller (among others). The diameter of the ballnut and screw would makes angular contact bearings quite costly. At first I drew it with the ballnut inside the bearings, however the following design allows for smaller 6007 bearings and also gives the option of putting 2 ballnuts in to eliminate backlash. One ballnut attached to either side of the shaft.

    Here it is:
    (I'll draw it in 3D if necessary)

    Click image for larger version. 

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    Black is ballnut/screw/bearings
    Red is shaft, steel or aluminium - probably aluminium since lower moment of inertia.
    Orange is thingy that fits on the end of the shaft and attaches to the ballnut via the 6 holes in the ballnut.
    Green is some aluminum plate to hold every thing. One plate will be extended to accommodate the stepper motor.
    Brown is timing pulley. I could machine the pulley on to the shaft, however that means making a new shaft if I get the number of teeth wrong.
    Blue is a collar bolted to the aluminium plate to preload the bearings.

    Any comments/ideas/criticism welcome!
    Last edited by Jonathan; 09-04-2011 at 02:34 PM.

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