Making auto leveling and/or mesh leveling work

About a year ago I posted how to modify the firmware to make mesh leveling work. I set the mesh to 6x6 and watched it go through it's paces before every print. I level the bed with a gauge clipped on to the print head and could even see the dip in the center of the bed. I got good printing results and never gave it a second thought.

Until, I read that after the G28 home command the auto leveling was turned off, so I never was using the mesh and did not know it. So I put in the required M420 S1 command after each home and left the bed unleveled. I could now see the Z stepper move up and down to compensate the bed. I then leveled the bed.

Arrrgh... on my micro porous glass bed the results were suddenly terrible, awful auto leveling. The problem was that it was absolutely repeatable, I was confused at the change. I decided that the IR sensor was sensitive to the reflectivity changes on different parts of the bed as the surface aged. I took the glass plate and turned it upside down so that I had clear virgin glass with the same reflectivity throughout. Success, I got perfect lines and perfect leveling.

So the question becomes: what surface is the best for the IR sensor.

 

I put a black sticker over the glass and got perfect results. My only problem is bonding is so great it ripped the surface apart. Now I am trying to find settings for optimum bonding and release.

I am always getting fooled. I thought I had changes in my auto leveling when I improved my manual leveling first. Correlation and causation are not identical. I have been happy without auto leveling for over a year and did not know it. The microporous glass is not good for the auto level, but is a great printing surface.

 

Okay, I am finally getting someplace. The homing command (G28)for x,y, z first touches the end stop switch then backs off and approaches more slowly for a second tap. The firmware has x,y with a "BUMP" of 5mm and z with a "BUMP" of 2mm. Makes no sense to me as the same end stop switches are used for all. I set the "BUMP" on z to 10mm. I use G36 and a 6x6 auto level mesh. The IR sensor also does a double tap in mesh leveling and is set to z half speed on the second tap. On the second tap I first went to from z 1/2 to z 1/4 speed and noticed a big improvement. I then went to z 1/8 speed and got even better near perfect. I have not yet gone to z 1/16 speed on the second tap.

z 1/16 does work even better albeit slow. The red LED flashes as it approaches the bed instead of just solidly pulsing on.

The priming line looks dead nuts perfect.

I guess what I should do is a G36 followed by an M500 and thereafter comment them out and just do an M420 S1 and recall the mesh.

I am judging the results first by the priming line down the left edge of the plate and finally by the printed part.

The IR board uses pulsed light to sense height so the discreet steps would be z speed dependent. I do not know what the second tap speed is that will no longer give improvement but I will find out. It is now completely useable on micro porous glass.

For any that are interested I can post where in the firmware these settings are.