Erratic Mesh Bed Leveling on start of prints
I've got a strange issue here. I recently turned my MK2s into an MK2.5s, and the Mesh Bed Leveling done before each print is either successful right away, or it will fail any number of times. I looked through the menu options to see if there's a way to find out why this is happening.
First I'll describe the problem: As we all know, the extruder will check 9 points in a 3X3 grid to perform it's mesh bed leveling. Normally the extruder 'hops' a few times at each point, and then it will begin it's print. What's happening with me since I did my upgrade is the printer will perform as always for the first three points (the ones closest to the front of the printbed). It almost always does the 4th point quickly. Most often, it will hiccup a bit on the 5th point, the one in the very center. It hiccups less at the 6th, even less so on the 7th, but 90% of the time or more on the 8th point it will look at the point once, Z up a bit more than usual, try again, and fail the print, asking me to raise the Z axis to the top. Sometimes it will repeat this for about 10 times, other times it will look at the 9 points, never acting as smooth as it did prior to the upgrade, and print away. It has never done the 8th point like it does the first 3.
Running the Setup Wizard, I am told my printer has no skew. Prior to the upgrade I had slight skew, which I went to great lengths to remove during the upgrade.
Things I thought might be a problem: When I changed from the non-magnetic printbed to the magnetic one, I felt like I had to push the bed into position so all four corner screws could be fastened. I left the printer in this state while I left for an extended trip, and have recently drilled out the four corner holes of the printbed frame with 9/64 inch drill bit to give the screws a bit more tolerance. The printbed fastened onto the frame easily after 'enbigenating' the holes.
I'm running Firmware 3.8.1-2869. I had this firmware on my MK3s, but this version firmware on the MK3s resulted in zero successful prints, so I backed down to 3.8.0 on that, and the MK3s is printing well again. I am suspicious of the 3.8.1 firmware.
When I had the printbed off to widen the mounting holes of the frame, i used a straightedge and a bright light to check for warping of the printbed and found none. I've flipped my textured PEI sheet to see if the problem moves, and it does not.
What I'm hoping is that someone is able to tell me some secret menu option that will let me see the Z values for each of the points measured during the Mesh Bed Leveling process. Or if anyone else has had this happen and can tell me what to investigate. It's so frustrating because sometimes the printer seems to be telling me things are so warped it can't go, and other times, with no changes at all, it's fine and will print with no issue.
RE: Erratic Mesh Bed Leveling on start of prints
There are many threads discussing this in depth, using both Octoprint and Pronterface to extract the numbers.
But you need to remember things change with temperature, both the physical bed and the PINDA sensitivity. So you can end up chasing your tail if you try to get too perfect.
But - the hopping is reading the point multiple times. If any given point is "out of range" the printer pauses, lets things settle, then tries again. Usually it's vibrations in the printer that cause this: and a wobbly table makes it worse. Folks have had good luck adding bricks to stabilize things, especially when the printer is in an enclosure like the Lack, which is pretty light weight.
RE: Erratic Mesh Bed Leveling on start of prints
I got it fixed. I'm not sure which of these actions specifically did it.
Applied a little torque to all the fasteners holding Z-Axis hardware in place. Some bolts were looser than I would have thought.
Enlarged the holes in the four corners of the printbed frame to relieve the pressure, unfastened the bed, allowed it to relax at 60 degrees, and then secured the bed again. (initial assembly of the 52 bed was difficult. One corner was a struggle to fasten.)
Cleaned all the dust and plastic dust from Z-Axis motors.