First Layer Issue - Middle of Layer
The printer has been working for the better part of a year. Today I printed a part just fine. Queued up the next part and it produced a spaghetti monster. Started the print again and watched it carefully. The edges of the part laid down fine. When it was filling in everything was going well until, towards the middle, the print head started lifting up a bit causing the filament to not adhere to the plate. It is as though there is an error in first layer height map at that one middle point. Has anyone seen this before? Any ideas as to what might be wrong? I cycled the power, hit the reset button, cleaned the plate and tried a different part, same result. It is always in the same spot.
Thanks.
RE:
Do the Z axis spindles get stuck? Is the print plate (approximately) level? The manual is uncertain whether or not to grease the Z-axis spindles, and there are multiple cases where they skipped steps after a while in operation. Related, check whether the threaded nuts are truly perpendicular to the printbed: Tightening their screws without causing misalignment and tension (that could later result in an axis getting stuck) is not straightforward.
I run "manual" Z axis calibration with print plate at Z=1 (after homing) and a credit card between nozzle and print plate as "feeler gauge" as the three Z motors are not individually controllable by software, and alignment happens by running them into the end stop during Z axis calibration. Which isn't particularly precise (if end stops at least were at a consistent depth...). Turning the spindles manually lets me align them easily to +/- 0.5 step.
RE: First Layer Issue - Middle of Layer
No issues with Z axis getting stuck. You can see in the picture that the print areas on either side of the problem area lay down just fine. That and when it laid down the edge of the box initially, those laid down fine. The plate is strong and flat. It sure seems to me like one of the center points, when doing the initial height checks, is off.
RE:
OK... is it possible that the nozzle is leaking filament during Z axis calibration? This could even be related to moisture, which would explain why it just stopped working. Have you dried the filament?
Edit: would seem odd being so consistent that it fails twice on the same spot. But, nothing is impossible.
The commonest cause of areas of poor adhesion are spots of oil or grease - try a thorough print-sheet clean and try again.
Cheerio,
RE: First Layer Issue - Middle of Layer
Thanks for the reply. That is an interesting possibility. I will try that. It does continue to happen in only one spot.
RE: First Layer Issue - Middle of Layer
Yes, I cleaned the plate and even switched plates with a printer that is working fine so I am sure it is not the plate.
OK, my next suggestion would have been to flip the plate... also to double check that no debris under, or on the underside of the plate, are distorting it. Also to hold a straightedge against the surface to check flatness.
Please confirm: This recurs with different print files, with different copies of the same print file. If with just one file transfer that specific file and medium to another printer - does the error follow?
You have swapped plates with another printer, try swapping nextruders ( work from major steps starting from step 21 of https://help.prusa3d.com/guide/6-nextruder-assembly_849034#849957 ) - does the error follow?
Cheerio,
RE: First Layer Issue - Middle of Layer
Problem fixed after chatting with the help desk. They had me update the firmware, I missed the Nov 24 version, always a good idea. Then they had me tighten up the two tension screws on the extruder. Neither of these really helped but a good idea. Eventually the issue was that various filaments need quite a bit different temperature. I was using Overture PLA black and cranked the first layer temp up to 245 with subsequent layer temp to 235. He said even different colors from the same vendor need different temperatures. I have been using Overture for years without issues using the default PLA temperatures. Not sure if the hot end thermistor is starting to go. I may buy and install a new one.
RE: First Layer Issue - Middle of Layer
I just remembered I had pinched the thermistor wire when initially assembling the printer. It was working fine so I ignored it. I'm about 95 percent sure this is my problem so I ordered another one.
RE: First Layer Issue - Middle of Layer
I just remembered I had pinched the thermistor wire when initially assembling the printer. It was working fine so I ignored it. I'm about 95 percent sure this is my problem so I ordered another one.
It is never bad advice to recommend buying spares. I have two sets of thermistors, heating elements and heat blocks.
RE: First Layer Issue - Middle of Layer
I agree. The thermistor is a critical element. I just swapped the hot end from the working printer and that fixed the problem so I'm now 100% sure it is the thermistor. Went ahead and ordered a new thermistor and heater because they are cheap, cheaper than the shipping costs.
RE:
Just a final follow-up. The parts finally arrived. It took what seemed like forever but they are now installed. I replaced the thermistor and the heating element. Using the same Overture black PLA that was in when the problem occurred I printed a one layer flat panel and that worked fine. I also printed string test posts since the last time I had a thermistor failed the stringing was really bad. The stringing is almost non-existent with the default slicer values. The issue was definitely the thermistor. These seem to be very sensitive, prone to failure. I like Hyiger's idea of always having spares. They are cheap and easy to replace.