Prints fail immediately, I am at a loss
I have been using my MK3 for a few months now and had next to no issues.
While printing with PLA I found that larger prints would start to warp where they were attached to the heated bed and sometimes completely detach, after some research it seems that the heated bed was a bit too hot (60C) for the PLA I was using, so I turned down the heat to the recommended (45C-55C). I set up a new filament profile and tried again.
had the print fail overnight and a massive blob of plastic was on the nozzle. cleaned it and suddenly nothing will stick to the bed when I try to print. Seemed like I was plowing through he first layer and my Z height was too low. so i begin to adjust it using the basic first later test. Nothing worked. again back online and started with the method described here ( https://shop.prusa3d.com/forum/-f6/life-adjust-z-my-way-t2981.html )
after the first few i noticed that even when I didn't change the Z halfway through i noticed that it was printing higher on the right side of the square and lower on the left. so i ran an XYZ calibration.
after a fair bit more test i finally landed on a near perfect result and went to bed, came back in the morning and did the EXACT same test without changing anything and it was printing too high on the left side about. so I changed the z value a few more times and landed on about -1.090 which seems fairly high.
so back to printing as normal?
well the first print i did didnt adhere to the bed and was getting pushed around as the trim was being made and the second just blasted right through and started to form a blob.
so I am completely at a loss as to how to start printing again, the only thing my printer can do now is this Live Z test, and that value is completely incorrect for other prints apparently...
I am printing with Hatchbox PLA, and using Slic3r to generate the G Code. I have tried a variety of heats and Z values and nothing works. I haven't been able to use my printer in a few weeks now due to these issues, and I am just completely at a loss, any help would be amazing.
Re: Prints fail immediately, I am at a loss
I had the same problem that a blob starts forming on my print. I noticed that my heat block was very loose. After re-tensioning it was fixed.
And cleaning the print surface from time to time with soap will help.
Re: Prints fail immediately, I am at a loss
Since the first one I haven't had any issue with blobbing (but also haven't left it long enough once I notice a failure)
When i do the regular First Layer Test, there is no issue, but immediately after when I try and print anything else i get this... 
I don't know why the first layer here isn't sticking?? if my first layer cal. wasn't working every time I would understand that, but this is just confusing me.
I will try tightening everything up and see if that helps, though the heat block and nozzle seem as tight as i can get them
Re: Prints fail immediately, I am at a loss
I will try tightening everything up and see if that helps.
Good idea. Check the x-carriage bolts and PINDA are secure. Either of those issues will make nozzle height vary unpredictably
Re: Prints fail immediately, I am at a loss
Tightened every bolt as much as i could (nothing tightened that much) , and the same result, prints the z axis test perfectly, then fails to print anything else...
should I be thinking about reassembly? or are there other avenues i could try first?
Re: Prints fail immediately, I am at a loss
Your problems are caused to almost 100% for two reasons, a dirty bed and / or wrong Z level.
Rule number 1
Wash the bed with detergent and warm water. Wipe with paper and do not touch the bed with your fingers.
Rule number 2
Make a correct adjustment of the Z level. Start with a "Calibrate / Calibrate Z. A correct Z level is just the thickness of two papers, 0.2 mm.
A lower temperature on the bed than the recommended one also results in a poorer result.
Bear MK3 with Bondtech extruder
Re: Prints fail immediately, I am at a loss
Wash the bed with detergent and warm water. Wipe with paper and do not touch the bed with your fingers.
I clean my bed with a micro fiber towel and Glass cleaner (Windex) should I be using something with stronger Alcohol levels?, this is the first time I've had these issues
Make a correct adjustment of the Z level. Start with a "Calibrate / Calibrate Z. A correct Z level is just the thickness of two papers, 0.2 mm.
once Z calibration is done how should I be testing for the extrusion height? just the first layer test? or is there a better way?
during tests it seems like i should lower the head, but during actual prints it seems like i should be raising since it appears to be plowing through the print...
EDIT:
okay after a few First Layer tests. it seems that my bed height is not even (or I'm printing unevenly on the bed somehow?), the height of the first layer WIDELY differs from area to area. Being pretty correct on the left side and center but printing WAY TOO LOW on the left, would this be what is causing the issue? and how would I go about fixing this? Ive re-setup the printer as well as done XYZ calibration several times now.
Just realized that the test prints never go over to the right side enough to truly affect it which is why they don't fail. which makes a lot of sense
Re: Prints fail immediately, I am at a loss
the best prep for your bed is to wash it with warm water and dawn dish soap (in the UK use Fairy liquid) by using a wad of clean kitchen paper towel dampen with warm water and put a dollop of Dawn on the pad and scrub (i do it twice at 90 deg to each other holding the plate by the edge as it is a phonograph record rinse under running water and dry with clean paper towel keep touching only by the edge... I do this every other day of printing with both kinds of plate.
then set your live z with this method https://shop.prusa3d.com/forum/assembly-and-first-prints-troubleshooting-f62/life-adjust-z-my-way-t2981.html it is far better than the zig zag method in the firmware
Re: Prints fail immediately, I am at a loss
I found my PLA prints on my Mk3 would fail like that sometimes, so now I always use the glue stick (bought a pile more of the Kores ones) and set the first layer speed to 20% with PLA, works great but with small flat parts it can be a little fiddly getting them off the spring steel sheet.
Re: Prints fail immediately, I am at a loss
hm okay ill try that, though it almost seems like the plastic either sliding off the bed or getting squished, im not sure anymore.
i dont know why both these tests seem to come out fine but actual prints made through slic3r still just break... same settings and all
Re: Prints fail immediately, I am at a loss
A gluestick making things better is proof your bed is dirty and needs cleaning.
Also, handling spools with bare hands will contaminate the filament. Oils on your hands - especially if you use hand lotions or sanitizers - are serious anti-stick agents for PLA. Your hands should never come into contact with the bed or the filament.
Hot Water wash: as needed
Handle the bed only by the edges.
Wash the bed in hot water, use a fresh paper towel as a wash cloth, with a few drops of plain dish soap (Dawn, unscented, no anti-bacterial, etc.). Rinse well in hot water - if you have very soft water, rinse a bit longer.
Dry the bed with a fresh paper towel.
Handle the bed only by the edges.
Place bed on printer.
Alcohol rinse: every few prints
Once in a while, an alcohol rinse is helpful.
Pour a 5 cm puddle of 91%+ alcohol in the middle of the bed, use a fresh paper towel to scrub the bed. Wipe up all the alcohol.
Streak test: when contamination is suspected and after a wash
With a fresh piece of paper towel, and very clean fingers, dampen the towel with 91%+ alcohol, and wipe the bed side to side moving back to front, like you're painting it with alcohol. The alcohol should be thin enough on the towel it quickly evaporates. If you see any streaks, the bed is dirty and needs a wash.
Acetone wash: infrequent
Pour a 2 cm puddle of acetone on the bed, scrub it around with a fresh paper towel. It will evaporate fast as you clean. This step removes PEI oxides that form over time and with heat, and improves PLA adhesion to a like new state.