Auto-Tramming Question

Red Sand Robot

Hello all,

I know that when configuring auto-tramming you are supposed to input the location of the leadscrews relative to the 0,0 point of the coordinate system.

Would it also work to put the point at which the bed is connected to the linear carriage/bearing? With the leadscrew attached to the same part that also connected to the linear rail carriage, would it not also be equivalent to use the location of the carriage as a reference point? Both the screw and the carriage constrain the motion in the z-axis, just curious about whether that would work or not.

droftarts

I don't think so. It's not the mounting point to the rail that the firmware can adjust, it's the movement along the axis, ie the leadscrew. That's what the levelling is calculated on.

Also, if you only have two leadscrews/motors on an axis, you can only correct automatically in one plane, usually X or Y. You need to have three or more leadscrews to correct the plane in both X and Y.

Ian

dc42

If there are 3 leadscrews, the firmware assumes that the bed is supported at 3 points and it can rotate about the X and Y axes at each of those points. This is what you would get if you used a 3-point kinematic mounting, or if the leadscrew nuts incorporated gimballed joints. The coordinates of those 3 points are what you tell the firmware, so that it can calculate how much tilt in the X and Y directions will be caused by raising or lowering each of those points.

If the leadscrews are attached to carriages which in turn support the bed, then the points at which the carriages support the bed are the points that the firmware needs to know.

If there are 4 leadscrews then the situation is more complicated, because movement of an individual leadscrew requires the bed to twist. The firmware assumes that the bed twists uniformly so as to have the commanded height at all 4 points. The true situation is likely to be more complicated than this, so additional iterations are likely to be needed to reduce the deviation at the probe points to low levels.

Red Sand Robot

@dc42 said in Auto-Tramming Question:

If the leadscrews are attached to carriages which in turn support the bed, then the points at which the carriages support the bed are the points that the firmware needs to know.

That is pretty much how my machine is set up, thanks for the information! Thought that might be the case but wasn't quite sure. Thanks!