First layer calibration problem  

RE: First layer calibration problem

Check for a loose grub screw on the extruder gear, open the extruder door, heat up nozzle, turn extruder to where you see the grub screw, tighten it down. Check if filament path is good or not good.(this checking needs to be done in a maintenance plan).

Check spring, to tight or to loose is not good. I have a mk3, without filament it the screws need to be flush with outside. With filament it should have 1 or 1.5 mm outside the part. Search in prusa manual for your model printer.  And the spring makes a lot of difference.

In general check the whole printer for loose screws. On the mk3 the idler screw for gears, that you can open, do not tighten this scew, it needs to be loose.

RE: First layer calibration problem

I don't understand why I would need to heat the nozzle (nowhere near the gears), so I skipped that. The grub screw was tight. I don't know if the springs lost some tension over the years. I tried the springs both more loose than normal and tighter than normal. Neither seemed to make a difference. I will go back and try to tighten all the screws/bolts that are part of the extruder. 

RE: First layer calibration problem

@bohemian73

You're describing a very typical nozzle clog.  You might do a few more cold pulls, post up a photo of the cone, and maybe someone can assist. 

Consider if you've ever printed glow-in-the-dark filament: if yes, might be time for a new nozzle -- the specs of material that glow are hard, don't melt, are often random and jagged and can build up and jam in the nozzle orifice. 

A less common issue is the thermistor is failing and the nozzle temp is dropping when you try extruding. About the only way to test this is an ohm meter to measure the thermistor when cold.

I think Peter was referring to extruding filament until you can see the set screw ... for which heat is needed. If no filament, then no heat required.

RE: First layer calibration problem

It started as a clog. But I no longer think it can be a clog after I replaced the nozzle, hotend and PTFE tubes as there was no filament when I tried the first level calibration again. 

I have only printed PLA and PETG> I tried a new nozzle as one of my first steps. There was no filament at the time I checked the set screw. I can try the thermistor. Thanks

RE: First layer calibration problem

You can have also temperature problem. Replacing the nozzle you can have temperature transmission problem between the heating block and the nozzle.

Did you use Thermal transmission lubricant between the heatblock and new nozzle.

RE: First layer calibration problem

Maybe you can post a picture of your first layer calibration square. That may help trouble shooting.

RE: First layer calibration problem

The arrow in the first picture shows where the filament things out after about the first 4 cm. The filament holds to the plate in those first 4 cm, but doesn't hold very good after it thins down to about 0.25mm diameter. Not a lot of difference at -0.850 or -0.950 either. 

I replaced the thermistor with the new hotend previously, checking to see that I didn't damage any wires. I haven't taken the time to check with an ohm meter. 

Not 100% sure if I used heatsink compound with the first nozzle change, but I believe I did. I just replaced the nozzle a second time, again with a new nozzle, and used headsink compound for sure this time. I also readjusted the PINDA probe and recalibrated the Z-axis. 

No difference for my first layer calibration. I had a couple of failed prints before I cleared the clog. I have have the problem where the filament thins out on the first layer calibration since I thought I cleared the clog. 

RE: First layer calibration problem

Nozzle is too high, you need to go more negative on z-offset.  Your print sheet is also very dirty with fingerprints, which isn't helping you at all.

RE: First layer calibration problem

I agree with @tim-2, looks like your z needs to be lower. 

Don't use the in-built method, as the small square is hard to read, especially if you're not experienced. Use this instead: https://forum.prusa3d.com/forum/original-prusa-i3-mk3s-mk3-assembly-and-first-prints-troubleshooting/life-adjust-z-my-way/

To quote @bobstro:
> In general, start high (less negative) and work lower (more negative) in large increments (e.g. 0.1mm) until the filament starts to stick on its own. When you've got your Live-Z setting adjusted properly, you should be able to gently rub the extruded lines on the PEI surface without dislodging them. Then start lowering (more negative) the level until there are no gaps between layers. You should not be able to peel the lines apart after printing, but the top should be regular.

RE: First layer calibration problem

As a note: you normally do not use thermal compound on the nozzle. The temps are too high for paste to work properly unless it is specially formulated for 200C +.  Compound is used on the heat-break to heat-sink threads.

How the hot end is reassembled can be an issue. There are tricks and secret handshakes required. The depth you set the heat-break can affect prints, for example. How well (and clean) the heat-break to nozzle seat can affect prints. Following the E3D-V6 assembly guide is fundamental to having a working extruder. And, even the cooling fan shroud install direction can affect prints (does it point too far up and air flows around the heater block instead of the nozzle tip). 

Get the nozzle height close to correct - so the first layer is 0.20mm thick - and then you'll be able to see if you have an extrusion rate issue. Because clogs cause gunk to build up in places you don't expect, like the teeth of the Bondtech gears, even inside the heat-break.  Both can cause under-extrusion.

RE: First layer calibration problem

adjusting the z offset to -1.1 (~0.21 mm thick square) or -1.2 (about 0.25mm thick square) seems to work. I guess I was obsessed with the reduction in size at the beginning of the calibration. I guess it is something I never noticed and thought that was my real problem. The first offset when the printer was new was about a third less than what I am looking at now. I will have to do it in the light tomorrow to get a good first layer. Not enough light at the moment.

Thanks to all the replies and help. 

RE: First layer calibration problem

@bohemian73

Actually - going from -1.100 to -1.200 should have made the square thinner. More negative lowers the nozzle towards the print sheet.

RE: First layer calibration problem

It feels like a common issue that most users who are new to this tend to not go low enough for the first layer calibration. A value around -1.2 is certainly well within the range. If it gets closer to -2.0 I would reposition the PINDA.

Also remember that using a different sheet may require adjustments to Live Z. The satin and textured sheets are quite a bit thinner than the smooth sheet, so you will need a more negative Z offset. Even within one category of sheets, manufacturing differences in thickness may require Live Z adjustment. And certainly, whenever I make changes to the hotend, even just a nozzle change, I do a quick Live Z check to make sure (because the new nozzle might be slightly higher/lower than the old one).

RE: First layer calibration problem

I don't understand why the thickness was greater when I used a higher negative z offset. However, everything is working now, so all is good.  I will have to check the z offset again if I get a clog or after a lot of printing. 

RE: First layer calibration problem

Zero offset is the default. Positive offset = larger distance between nozzle tip and bed comparing to default. Negative offset smaller distance between nozzle tip and bed.

RE: First layer calibration problem

@bohemian73

If you go a bit too low then you get slight ridges in the layer as it pushes filament around. This has the effect of making a sheet measure thicker when peeled off as you are measuring the high peaks rather than the true thickness.