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Determine tolerances for x axis leveling system
Closed, WontfixPublic


Looking at some red tag machines, we have noticed that there is a variance from parallel between the plane defined by the surface of the bed and the plane that contains the line defined by the x-axis after the automatic "level x axis" gcode is run. There have been some instances where shimming one side of the x-axis during the "level x axis" sequence will bring a machine into compliance with the skirt height requirements outlined in the hibiscus OHAI. The theory is that there is a correlation between the degree to which the x-axis is out of level, and the inconsistent skirt measurements. We would like to know if this is the case, and if so, we would like to know what the tolerance for parallelism between the bed and the x-axis is and how to measure and adjust it so that we can add it to the final assembly instructions and prevent non-conforming printers.

The auto-leveling system will compensate for this to some extent, but I suspect there is still a positive correlation between x-level relative to the bed and skirt height consistency. @marcio do you have an idea of how far out of level the x-axis can go before the G29 z-axis compensation can no longer adequately correct?

Event Timeline

kent created this task.Sep 26 2018, 1:48 PM
kent triaged this task as Normal priority.
kent updated the task description. (Show Details)Sep 26 2018, 1:51 PM
kent added a comment.Sep 26 2018, 2:12 PM

Here are a couple photos I took of a hibiscus machine that illustrate an example of what I think might cause the x-axis to be out of level. For these photos, we put a straight edge on the bed, and then put another ruler against the bottom of the sheet metal frame. The four measurements of note are the distances from the bottom sheet metal to the top of the z-motors, and the distances from the top of the straight edge on the bed to the tops of the z-motors.

To me, it looks like the z-motors themselves are both at 94mm from the bottom plate, but the distance from the straight edge to the z-motor is 4.5mm on the left and almost 6 on the right.

kent updated the task description. (Show Details)Sep 26 2018, 2:25 PM
tutley added a subscriber: tutley.Sep 27 2018, 8:54 AM

@kent since the measurement to the z motor mounts from the bottom plate is consistent between the two sides, that must mean the y axis is not parallel to the bottom plate. There are a lot of opportunities for tolerances to stack up here and cause this. The mount flanges on the bottom plate are some tolerance out of parallel from the plane of the bottom plate, then there can be bloom or crooked printed parts that mount the y rods, then the bushings, then the printed parts for the bushings, then the bed plate itself, then the flexy corners/standoffs that ultimately determine how the glass sits. we could adjust the double or single bearing holder to compensate for this to some degree if they are all coming out biased in the same direction.

kent added a comment.Sep 27 2018, 9:37 AM

@tutley thanks for looking at this. I'd like to do some experiments with quiver to determine how far out the bed can be relative to the z-motors before it starts becoming an issue.

nickp changed the edit policy from "All Users" to "LulzBot Hardware Products (Project)".Oct 25 2018, 12:01 PM
kent closed this task as Wontfix.Nov 26 2018, 4:13 PM
kent added a subscriber: oliver.

@oliver did some experiments and concluded that this does not make as much a difference as originally suspected.