Prime line suddenly too low on Z

So for some reason that I can’t seem to figure out, when I start a new print the extruder seems to be WAY too close to the bed (smooshing the filament into the bed to the point where I can barely scrape it off) but then when it goes to do the first layer of the model it seems to be at the correct height. I haven’t changed anything in my start g-code or anything else. I re-levelled the bed just in case but that’s fine too. Does anyone have any thoughts as to what it might be? It was all working perfectly before I went on vacation but when I came back suddenly it’s weird.

Separation anxiety?
But seriously. Are you Leveling your bed hot?
If so, I’d consider an electronic compensation tool, like Bltouch.

And just to be a total dick, is there any detrius between your bed and the plate?

I’ve been binge watching Archer, sorry.
Really does sound like a warped bed, if what you say is true, and no teenagers or soviet spies have been up to no good in your absence.

Haha might be. “YOOOOU LEFT ME!!!” :wink:

I always level hot and I have a BLTouch. I use the bed visualizer in Octoprint and it looks nice and level. I also use the tramming wizard after I level manually. But the really weird thing is that it was printing fine (in terms of the purge line) and then suddenly it wasn’t. I have one theory I’m about to test but otherwise I’m at a loss.

Well this is weird. I did another mesh test for the visualizer and this time I get this:

What the hell?? I would have expected along that side it would have been higher but to see it that sharply lower is just bizarre considering it was mostly green over the whole bed last time I checked it.

Do you have a flexible build plate? It is positioned properly ? Time to re check the bed.

That is very odd. It might not be the best idea but perhaps adjusting the Gcode will save you nozzles.

G1 Z0.4 F1000.0 ;Move the extruder to 0.4mm above the print surface. You could add a command to lift the nozzle up some.

Nope - regular Creality CR10s Pro bed.

Nothing else has changed since the last time it worked properly. I’m at a loss to explain it. The weirdest part is the fact that after the nozzle grinds against the build plate (and hits the bed clip) doing the prime line, it prints just fine. I did a 1 layer object and it measures to 0.22mm. I would have expected it to be squished to the point of near transparency but it is just fine. IDK

So the bed is fuct or the sensor.
Either way, it’s because you left them.

Again, is there anything under the bed?

If not, may I suggest a run without the Bltouch.

No, nothing under the bed.

Your sensor thinks the bed drops off, so the machine is compensating accordingly, according to your handy visualization tool.
I’d give that sensor a swift one upside the head, but I’m old-school.

My purge lines are always flatter then the rest of the first layer but they do come off OK, usually. Could be gremlins.

Yeah I’m not worried about them being perfect. They’re always a little off but the sudden and drastic change is concerning.

According to this statement (smooshing the filament into the bed to the point where I can barely scrape it off). Your z-offset is too close to the build bed,

Assume the build bed is leveled and cleaned, I would suggest you use the brim for build bed adhesion (5-10 lines with a line distance of 0.2mm), while it’s printing the brim, fine-tune the z-offset by baby steps (/menu/tune/probe z-offset value), once you get the brim line fused together like the poly sheet, and save it (/menu/configuration/save settings).

BTW there are different z-offsets for varied materials, typically the PETG does not like to be squeezed as the PLA, e.g. PLA = -1.50mm, PETG might be =1.25mm or so.
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Thanks for the reply. Oddly enough the z-offset is fine for everything other than the priming line. And the priming line was fine until a couple of weeks ago and I haven’t made any changes directly to the start code so I’m struggling to understand what the issue might be and how it happened.

Gremlins again

I believe it!!