Ok boys and girls, here is my story:
I am having serious problems with under extrusion when printing PLA on my UM2. This is what I can remember doing to/with the printer since I got it around 9 months ago:
Printer arrived with 1 reel of silver PLA from UM.
I used this material exclusively on the printer with no problems until it ran out.
I then tried some Verbatim 2.85 PLA. This worked a few times but eventually the feeder kept grinding into the filament, which prevented it from working.
I then switched to some ABS I had lying around (not sure which brand), which worked better. Eventually the nozzle became blocked and nothing would come out. This is when I discovered the Atomic cleaning method.
I tried the Atomic method a few times with both PLA and ABS but could never replicate the results shown online. The ABS would always just snap off around the level of the teflon coupler while the PLA would come out stringy rather than nozzle shaped. I did not appear to removing a whole lot of dirt from inside the nozzle either.
Eventually I found some 0.28 wire and used this along with the Atomic method, which made a bit of a difference.
I then tried some new UM 2.85 PLA but was getting very bad under extrusion.
I then switched to some Reprapper 2.85 ABS, which worked a bit better, but eventually the under extrusion came back.
Eventually the nozzle completely clogged again so I decided to disassemble and clean it.
Unfortunately, when removing the setscrew holding the temp sensor in place, it sheared off and trapped the temp sensor. This then broke when I pulled it out.
UM sent me a new nozzle kit, which I reassembled into the printer.
I started printing with the Reprapper 2.85 ABS and this worked great up until now.
Recently the nozzle became blocked again so I used the Atomic method a few times with ABS, then tried the Atomic method with PLA a few times before trying to run some PLA.
I had to use my 0.28mm wire again a few times before all the old ABS would come out and could finally start printing with the PLA.
So this is the first time printing with UM 2.85 PLA since replacing the nozzle but I am getting exactly the same under extrusion problems as before!
I have since used the Atomic method a few times with the PLA before switching back to the Reprapper ABS and it is printing fine. But I really want to be using PLA!!!
I cannot for the life of me work out why this is happening. My next step will be to disassemble the nozzle again to check for dirt but I don't understand why the first PLA worked best of all the materials and now I cannot print PLA at all.
UM PLA worked great
Verbatim PLA under extruded
Random ABS worked
Eventually random ABS under extruded
Used the Atomic method
UM PLA under extruded
Reprapper ABS under extruded
Eventually nozzle became blocked
Reprapper ABS worked
Eventually Reprapper ABS clogged nozzle
Used the Atomic method
UM PLA still under extruding
Reprapper ABS working fine
For printing PLA I use the default settings (210 nozzle, 60 bed, 50% fans). I tried +/-10 degrees nozzle temperature on a few prints but this made little difference.
Before replacing the nozzle I used default ABS settings (260 nozzle, 90 bed, 50% fans). Just before changing the nozzle I changed the settings to 250 nozzle, 110 bed, 0% fans, which gives a good result for me.
I have checked all of my filaments and they are definitely closer to 2.85mm than 3.00mm. The only other thing is that when the PLA under extrudes, the feeder grinds it down and you can see filament dust being pulled into the Bowden tube. However, I do often blow some compressed air through the Bowden tube to clean it when messing around with changing materials.
Any help on the matter would be greatly appreciated,