Auto_Bed_Leveling: Enhanced G29 command

[Roxy]

Well, here is something I have been wondering about for a while now but what is the purpose behind raising and lowering the arm between each probing? I see absolutely no reason for it and on a delta printer it doesn't do that. Makes very little sense to me to keep raising and lowering the arm/switch between probings when you can just lower the arm (before probing the first point), keep everything else the same, and after the last point is measured raise the arm.

Well... Think about this.... The Auto Bed Leveling code for Marlin was done by somebody truly gifted about a year ago. He coded up the pattern that you are seeing. And certainly, on the surface, it makes sense. Lower the probe until it touches, back off a little bit and re-take the measurement at a slow speed for increased accuracy. And then raise the probe a safe amount and move to the next point. Part of this was he was trying to make the code general purpose so it would work on most people's machine. But a big part of it is he was just trying to get it to work. And once he found a solution to a problem, he moved on to the next show stopper.

Since then, only a few changes have been made. Marlin doesn't have as many firmware developers as it deserves to have. So... There are going to be things that seem like they should be changed, but not enough people are playing with it to make it happen.

A good example is this: The original developer obviously did not have a Z-Probe that had to be raised prior to retraction. But a fair number of Marlin users do have this condition. That 'fix' had to be added after the fact. He didn't realize this condition even existed because he never saw it. If he had seen it, none of us would have seen it because it would have been fixed before we got the code.