S3 Incorrect auto-leveling

[Vitalmechanics 0]

Our printer is consistently seeing a low spot in the middle of the bed which isn't there - I've tried manual leveling with the same result. Something I've noticed is the whole print head rotates up a little as it's coming into contact with the bed in some spots. Could the bearing be loosely seated?

[Smithy 1,144]

Can you check if the glass is really flat? Maybe turn the plate and print again, just to see if there is any difference.

 

That the printhead is push up a little bit is normal, but you should see this also in other spots during the leveling.

[Vitalmechanics 0]

I've cleaned and flipped the glass bed upside-down, and the same thing seems to be happening (maybe in a different spot):

How much play is normal on the print head? I can jiggle the nozzles forward/backward (along Y) by maybe 1 or 2 mil with the rods locked.

[gr5 2,172]

Make sure none of the 4 long screws at the top of the head are loose.  I removed the rear 2 to check the connector and forgot to put them in.  I did a few prints like that!  quality was worse.  The head rocked quite a bit around that shorter bearing - like as you describe.  Probably not your issue.  You probably have normal "play".

 

The glass is tempered and the way the glass is made it's higher in the center - I mean the original sheet which is a few meters wide probably.  I think Ultimaker specifically gets glass cut only in the center to get the flattest possible tempered glass (I think it's a mistake to use tempered glass but that's another topic).

 

Anyway as a result the glass tends to be higher down the middle front to back or sometimes more like just thicker in the center like a tiny mountain.

 

So then when you level at the 3 screws what happens is the rear 2 corners tend to be quite a bit low and the center tends to be pretty close but a bit high.

 

Check the glass while attached to the bed with a straight edge.  If it's more than 0.3mm higher in the center you should maybe demand a new one from your reseller.  This happens sometimes (people demand better glass) and it's kind of expected I think?

 

But also note that it takes only an ounce (200 grams) of force to bend the corners of the glass up.  Just the weight of the glass on a flat surface with some thin coins (dime?) will make it flat again.  So for me I just bent the hell out of that aluminimum plate underneath until it made my glass flat.  But then I realized the other side of that plate is a circuit board with easily damaged traces!!!! Oh no!! I was lucky though - no damage.  🙂

 

 

 

[gr5 2,172]

Oh - I just saw you said "S3" in the subject.  Active leveling should compensate for the glass being higher in the center.  Hmm.  WTH?  Watch it level - when it's probing in the center is it touching the bed for a longer time than other areas?  If so then there is probably a spring issue.  Either the core spring is a bit weak or the springs in the bed are too stiff/tight.

[Vitalmechanics 0]

Update: tightening the screws on top of the printhead seemed to help, so thanks! Not sure why or how they were loose out of the box but it's now printing level.