I've thought about this a lot and I really don't like it. The Tina2 (and I presume Tina2S) works like this:slybunda wrote: ↑Sat Dec 16, 2023 5:11 pm Also iv added tye Z screw stabiliser mod that you print from thingyverse and add in a bearing to cut down considerably on gantry tilting.
And here is the Z screw mod i used:
https://www.thingiverse.com/thing:6050289
The Z axis motion is constrained by precision guide rails at each end of the X axis gantry, and the gantry rides on these rails with linear bearings. The gantry is positioned in Z by a lead screw attached to a motor at one end, and passing through a captive nut fixed to the gantry so that as the lead screw rotates, the thread causes the gantry to move up or down.
The alignment of the gantry is ensured by the guide rails, not the lead screw.
Without the "stabiliser mod", the top end of the lead screw is left free to move. The bottom end is attached to the motor via a flexible coupling, Without the flexible coupling, any misalignment between the motor, the lead screw, the guide rails, and the captive nut would impose a bending strain on the motor.
In my case, my Tina2 lead screw has a few mm of bend in it. This still works, because it is only fixed in two places: the flexible coupling at the motor, and the captive nut on the X gantry. The top end has to be free to waggle around – if it were fixed, then the captive nut needs to be free to move within its attachment to the X gantry sufficient to accommodate any misalignment of the lead screw relative to the guide rails, and also the amount of bend in the lead screw.
I believe there is some sliding movement in the captive nut, but limited and not necessarily sufficient to accommodate a substantial bend in the lead screw. Leaving the top end of the lead screw unconstrained provides for this, and removes the need for the captive nut to slide (except to self-adjust to the XY location of the bottom end of the lead screw).
The top end of the Z lead screw is unconstrained BY DESIGN, not by oversight.
Why is the lead screw bent? Not deliberately, but simply that high-precision lead screws are (probably) expensive, and it is cheaper to have two precision guide rails than a precision lead screw.
My guess is that slybunda has a lead screw much straighter than mine, but nonetheless adding the top end stabiliser should not produce a significant improvement. If it does, I suspect the linear bearings are not within spec (worn), or perhaps the guide rails are not fitted properly (my Tina2 had a loose guide rail when I received it - second hand - and I had to partially disassemble the housing to re-seat it). With a significant bend in the lead screw, fitting the stabiliser will cause binding and potential misoperation.