role of first layer calibration and live z adjustment
I just built my MK2S. Got it working perfectly, very high quality prints, happy! But I'm a bit confused about the several things you can do with z. First there is the auto z adjustment. Then there is the first layer calibration (V2Calibration). Then there is the live z adjustment.
I noticed if I only do the auto z adjustment, upon booting the system will prompt me to do the first layer calibration. But isn't the first layer calibration just a particular print? Or does it actually contain an auto calibration function? And if so how does the machine know I have done the calibration? (Because that warning at boot goes away after printing this thing.)
My understanding is that the machine can never know the gap between my PINDA probe and the nozzle tip, so z calibration can never be 100% automatic. No matter what one needs to do live z adjustment to get the z height perfect. Is my understanding right?
My printing surface doesn't seem to be perfectly flat. Despite the PINDA auto compensation, there is a spot on the plate where the first layer is looser. Will need to do a proper test, like printing a huge single layer square to find out.
Re: role of first layer calibration and live z adjustment
Check out my post here:
The manual has the bug, not the firmware... but if you read through the post, you can fine tune the bed leveling and your Z adjustment to get pretty consistent prints with a first layer that is nearly the same across the bed.
Re: role of first layer calibration and live z adjustment
I noticed if I only do the auto z adjustment, upon booting the system will prompt me to do the first layer calibration. But isn't the first layer calibration just a particular print?
Correct, all it does is print some lines giving you some very limited time to use "Live Z-adjust" to set a proper offset. There's one more thing to it though: at the very end of the print it sends one additional command to the printer saying "Ok, the user has completed Live-Z adjust"and the printer stops bugging you about it. If you look at the v2calibration file in a text editor you can even see the code (its actually 2) and copy it to create your own version of v2calibration if you want. JeffJordan did and created a much better version that can be found here: http://shop.prusa3d.com/forum/prusa-i3-kit-building-calibrating-first-print-main-f6/life-adjust-z-my-way-t2981.html
My understanding is that the machine can never know the gap between my PINDA probe and the nozzle tip, so z calibration can never be 100% automatic. No matter what one needs to do live z adjustment to get the z height perfect. Is my understanding right?
For all I know, with this type of sensor, that is true.
My printing surface doesn't seem to be perfectly flat. Despite the PINDA auto compensation, there is a spot on the plate where the first layer is looser. Will need to do a proper test, like printing a huge single layer square to find out.
Most bed aren't perfectly flat, yes. Mine has a bowl shaped "valley" in the middle. Here's what I do, which is working well for me: First I set my Live Z-adjust offset to get the offset as best I can for the center of the bed.
After that, I use bed level correct to try and counter the "unlevelness" by adjesting front / back / left / right sides. As Chad already mention. a negative number will lower distance from nozzle to bed, a higher positive number will increase that distance. I like to use this test print fr that purpose: http://www.thingiverse.com/thing:1831902
Using bed level correct and Live-Z adjust for the offset, i can work around my beds imperfections.
Hope this helps
Re: role of first layer calibration and live z adjustment
I used the +/-50 setting under Bed Leveling to no avail.
Then accidentally, when I was messing with something else, I happened to press on the right smooth rod in the rear and heard a small click. That's the problem--during moving the printer the right smooth rod had popped out a bit, leading to higher bed on the lower right corner (when bed moves to the rear the right gets raised). After that I redid the z test and everything turns out perfect. I then tightened the zip ties; I didn't do it tight enough such that the rod popped out. This is one precise machine!! Any bit of installation inaccuracy will show in the print.