Auto_Bed_Leveling: Enhanced G29 command

[Roxy]

What good is the gcode because it isn't adding the offsets from the G29 and that is what will possibly crash the head.

The Auto Bed Level Correction is done entirely on the Printer side of things. The G29 will tell you the 3x3 Bed Level Correction matrix that it generates. Once it has that, any coordinate it gets from the GCODE is multiplied by that matrix to 'correct' it for your printer.

I have my bed on springs so if a mistake happens, I usually have time to press the reset button. But one thing you can do is add a little more offset from your Z_PROBE_OFFSET number and verify things make sense by just printing in the air and see if the gap look reasonable. And then maybe cut the extra gap in half and try again and verify everything is reasonable. And cut in half again... It is extra time and effort, but if you are worried about destroying things, it is a way to get there safely.

Alternatively... What I did the first time was I had Safe Z Homing turned on so it would do the G28 in the center of the bed. I did the G29 and moved back to the center of the bed. I moved the nozzle to about 1 or 2mm from the bed and then started moving to each corner. The nozzle should stay the same height from the bed at each corner (because the bed leveling will be active after the G29). If you confirm that, you should have some level of confidence things are going to behave correctly.

[AbuMaia]

But be careful when using Pronterface to *not* use the Home X or Home Y buttons after doing a G29. They will erase the G29 matrix just like a G28 does.

[Roxy]

But be careful when using Pronterface to *not* use the Home X or Home Y buttons after doing a G29. They will erase the G29 matrix just like a G28 does.

Are you sure of this??? I've been using Home X and Home Y and I don't think that has been happening to me. But now I'm concerned! I guess one way to know for sure is to add a quick and dirty command to print the Bed Level Correction Matrix. If any home operation is clearing it, doing this would prove that was the case... (print the matrix to prove it isn't at unity, do a Home-X, and then print the matrix again to see what happened.)

UPDATE: Damn! AbuMaia is absolutely correct on this!!!! I added a command to print the Bed Level Correction Matrix and sure enough, it goes to unity if any Home operation is performed. I didn't realize the PronterFace Home buttons were using the G28 command to do their work.

[DarkAlchemist]

You can directly enter a GCode command. You could tell the printer to move to a given coordinate with that level of precision. Specifically, G1 X 10.1111 Y 20.0001

Of course I can but that wasn't my complaint and I can arbitrarily tell it anything but the mechanical parts is what dictates if it really can do what I said or not.

[DarkAlchemist]

The Auto Bed Level Correction is done entirely on the Printer side of things. The G29 will tell you the 3x3 Bed Level Correction matrix that it generates. Once it has that, any coordinate it gets from the GCODE is multiplied by that matrix to 'correct' it for your printer.

Which is exactly what I was saying because my uploaded gcode means absolutely nothing in the end.

I have my bed on springs so if a mistake happens, I usually have time to press the reset button. But one thing you can do is add a little more offset from your Z_PROBE_OFFSET number and verify things make sense by just printing in the air and see if the gap look reasonable. And then maybe cut the extra gap in half and try again and verify everything is reasonable. And cut in half again... It is extra time and effort, but if you are worried about destroying things, it is a way to get there safely.

Not sure I would see a change as it glided into position though.

Alternatively... What I did the first time was I had Safe Z Homing turned on so it would do the G28 in the center of the bed. I did the G29 and moved back to the center of the bed. I moved the nozzle to about 1 or 2mm from the bed and then started moving to each corner. The nozzle should stay the same height from the bed at each corner (because the bed leveling will be active after the G29). If you confirm that, you should have some level of confidence things are going to behave correctly.

When I do a G28 my head moves to the middle of the bed as well.

I like that last part but how would I measure it? Just do the M114 G92 tricks and see if it stays -2.1?

[DarkAlchemist]

Are you sure of this??? I've been using Home X and Home Y and I don't think that has been happening to me. But now I'm concerned! I guess one way to know for sure is to add a quick and dirty command to print the Bed Level Correction Matrix. If any home operation is clearing it, doing this would prove that was the case... (print the matrix to prove it isn't at unity, do a Home-X, and then print the matrix again to see what happened.)

UPDATE: Damn! AbuMaia is absolutely correct on this!!!! I added a command to print the Bed Level Correction Matrix and sure enough, it goes to unity if any Home operation is performed. I didn't realize the PronterFace Home buttons were using the G28 command to do their work.

Ugh, but this explains why I could press one of those buttons and it stopped doing the stuff when I moved X or Y. Damn, Pronterface just seems wrong to do any of this. What I mean is just shut up, sit down, and ONLY be a Gcode host. No BS just send Gcode from me, a button, or a file and stop "eating" letters like N/n and BS like using G28 to do your nasty work. Seems to me Pronterface needs to be rewritten to remove these things that are now interfering with progress and the newer routines/stuff being written.

[Roxy]

Which is exactly what I was saying because my uploaded gcode means absolutely nothing in the end.
Not sure I would see a change as it glided into position though.
When I do a G28 my head moves to the middle of the bed as well.

I like that last part but how would I measure it? Just do the M114 G92 tricks and see if it stays -2.1?

I would probably move to a corner, and use some feeler gauges to find the distance. Or, find something else the right size. And then use that to compare the next and the next corner. At all times, there would be enough of a gap you could move safely to check things out. And I would be double checking things with the M114 command.

[DarkAlchemist]

I have no feeler gauges but I was doing the math and my leadscrews + 1.8 degree 1/16 steppers means I have a revolution on my Z axis of 0.00025mm per step (takes 4000 steps to equal 1mm of travel). So, that number, or larger, my mechanical parts will do.

[Roxy]

I have no feeler gauges but I was doing the math and my leadscrews + 1.8 degree 1/16 steppers means I have a revolution on my Z axis of 0.00025mm per step (takes 4000 steps to equal 1mm of travel). So, that number, or larger, my mechanical parts will do.

It doesn't have to be as accurate as a feeler gauge. You could raise the nozzle and put something like a dice under it and carefully move the nozzle down so it almost touches it. Then take the dice out and move the nozzle to one of the corners. Slide the dice under the nozzle and see if you have very close to the same clearance. And then do the next corner.

[DarkAlchemist]

This is what always confuses me because I see my origin is the front left corner BUT g1 X0 Y0 doesn't put me in that corner.