1. #1
    Evening all. Heres my take on an easy to build and strong Z axis/carriage design when using supported rail.

    Y axis beam is only a starting point and the ball screw is probably not in the optimum place but the main design points are:

    • Distance from Y axis rail to cutter centre minimised (130mm with 80mm spindle) to reduce torsion on y axis bearings from cutting force and weight of Z carriage
    • Simple design with minimum parts and therefore deflection.
    • Z axis motor mounted on Y carriage
    • Lower bearings wider spacing to increase rigidity and reduce racking on ballscrew (bearings travel through gantry sides so y axis can be kept short.

    Click image for larger version. 

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    This is only a Concept design for bearing and rail orientation - final dims and size to suit cutting application

    Z axis

    16mm rails
    100mm travel
    80mm spindle (eg water cooled from ebay)

    Y axis
    20mm rails

  2. #2
    I think the difficulty with your idea lies with achieving sufficient accuracy on both axes, but particularly Z, to be able to mount the linear bearings. Normally people orientate the joints on Y such that at least one pair of bearings can be adjusted relative to the other, so assuming the rails are parallel that means the bearings will run smoothly. With your proposal, this could be done on Y or Z, but probably not both, which leaves the problem of machining the parts sufficiently accurately so that adjustment is not required. It's manageable if you have a suitable size milling machine, but probably impractical otherwise?
    Last edited by Jonathan; 20-05-2013 at 02:05 AM.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  3. #3
    I see your point but I don,t think its a deal breaker, shims in the mounting pockets or grub screws pressing on a metal plate between the bearing (like a jib in a dovetail) would easily give the required adjustment.

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