Two ballscrews on both X and Y axis?

[Jonathan]

On my router the distance, measured parallel to the X-axis, from the Y-axis (across gantry) ballscrew and spindle centre line is about 300mm. This allows the tool to deflect in the Y direction since the support is effectively 300mm away and the aluminium in between and the screw will bend since the linear bearings offer little support...



The obvious solution to this is to put the screw closer to the spindle (ideally intersecting the axis of rotation of the spindle) but realistically it's still going to be at least 120mm away.

So why not put another ballscrew on the other side of the Z-axis and add a second gantry cross piece on which one linear bearing will rest? Then the distance makes little difference and you've also pretty much eliminated the problem of the gantry twisting and helps with racking:



(Bad drawing I know... add one ballscrew mounted beside each of the Y-axis rails.)

Clearly the added cost of a second ballscrew is prohibitive (£65 for me), but I think it's worth the extra. I would probably link the two screws with a timing belt as adding another stepper and driver is expensive.

Tricky bit is mounting the Z axis ... I could use the same argument to have 2 ballscrews on Z, but that's getting rather silly.