First layer calibration woes  

New Member

I'm having a hard time getting my first layer dialed in.

On a clean sheet (wiped down with 70% isopropyl alcohol), and Prusament PLA, I can only get bed adhesion on the corners of the pattern at a Z depth of -1.133 (arbitrary value from a calibration session this morning).  However, with that Z depth, I get roughness on the top surface of the final plate like that shown here.

If I back the depth off to -1.115, the surface roughness is still there, but the corners aren't sticking properly.

If I back the depth off to -0.91, the surface roughness of the final plate is gone, but the PLA loses adhesion for several centimetres at a time.

I've adjusted the hotend height as high as it'll go to fix the clicking extruder problem already, but subjectively (and this is my first printer, so I could have the wrong intuition) it feels like it needs to go even higher.  It feels like I've still got a flow rate problem.

Is it worth trying to screw the heatbreak further into the heaterbock?  How can I tell if the PTFE tube is pinching? Is there something else I should be looking at?

Posted : 25/05/2020 1:40 pm
New Member

So the last print I did came out really well bumping the bed temperature for the first layers to 70 C.  Does that sound reasonable?  

Posted : 29/05/2020 6:58 pm
Illustrious Member

70C is a bit high for PLA. It will be great for adhesion, but there's a good chance you'll get some "elephant's foot" distortion at the bottom. 

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 30/05/2020 7:09 am
Trusted Member

A bed temperature 70 is a bit high for PLA, in general you should be able to print just fine with 60. A couple of things to note:

  1. You're using 70% isopropyl alcohol, PRUSA recommends 90%. In all honesty I use 70% because its in the house and I have difficulty finding 90%, but nevertheless in theory you're leaving trace amounts of contaminants on the bed which would reduce adhesion.
  2. Is it worth trying to screw the heatbreak further into the heaterbock? NO! The Mini should be properly assembled and calibrated when you receive it. There's many other things to check before you consider that.
  3. How can I tell if the PTFE tube is pinching? This will almost always result in under-extrusion, you would notice it as subsequent layers being thin or lacking material. You also might hear a clicking sounds from the extruder.

The link you provided describes your situation well, it sounds like you have an adhesion issue, not a Z-height issue. If you are getting that "scratched" surface area then the nozzle is simply too low. But if it doesn't adhere to the bed then it could be either 1) the nozzle is too high or 2) the nozzle is at an appropriate height but you are not getting adhesion.

So things to try include:

  • Make sure you are using the latest firmware for the printer and the latest slicer.
  • Check the Troubleshooting Your Mini page: LINK
  • Note that Mesh Bed Leveling I believe is done automatically as part of the First Layer Calibration but it can be done by itself via the menu.
  • Note that changing between textured sheet and smooth sheet requires a re-calibration of Z height.
  • Make sure you have cleaned the sheet properly - keep in mind touching it leaves oils behind which can ruin adhesion.
  • Make sure you are using "good" filament. Filament is like a sponge to humidity - old filament that has absorbed moisture will not perform as well. (Always store filament in dry environments, 15% humidity).
  • Make sure you are using the recommended temperatures for the nozzle and bed for the BRAND of the filament you're using. Even PLA temperatures vary greatly, e.g. Prusament PLA is 215C but Hatchbox PLA is 180 - 210C. I can't tell you how many times I've seen people using the wrong temperature. (Side note - if you save objects as GCODE files you run the risk of using the wrong temperatures when you change filament brands.
  • I prefer to adjust Z-height with a 100mm x 100mm square - this gives you plenty of time and plenty of visibility during adjustments. You only need to print the first layer of this square.
  • While printing the square raise the Z height until the roughness just disappears, no more.
  • At this point the square should adhere (although the nozzle may be lower than optimal if the bead is very flat). If it doesn't adhere, try 1) printing it on different areas of the build plate (back left or forward right for example) - perhaps there's an issue with just that area of the sheet and then 2) if it really doesn't adhere anywhere, get the glue stick out (after the sheet cools) and put a minuscule layer where the square will print. If it sticks then you may have an issue with adhesion to the sheet, not the Z adjust.

BTW on my MK2 I found that having trace amounts of residual glue stick left on the PEI sheet actually worked out perfectly, although that is a very different situation. On my MK3 (both smooth and textures sheet) and Mini I've never had to do that but there's nothing wrong with that technique.

As a last resort my friend had endless first-layer issues with his MK2 and we tried everything...well almost everything. We eventually did a full Factory Reset, which zeros out all the saved calibration data, and we started from scratch. (He was also using some (old) original Prusa Gcode  for calibration so we sliced the square I mentioned above with the latest slicer). After doing that the printer worked perfectly. It seems to me some values that were being stored in the printer were not being cleared out during our previous attempts but to be honest I really have no idea. Anyway I would do this as a last resort as it complete clears all values in the printer.

Good luck - let us know what happens.

Posted : 30/05/2020 4:09 pm

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