More Z offset problems  

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My Ipad seems to have struggled posting the right images. These are the ones I intended to post.

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what filament is it? already used before with success?

the awful is the second layer?

is that bad only in the large middle triangle or the small ones as well?

RE: More Z offset problems

Thanks for the reply. When it's bad the middle is awful and the outer ones are poor but you'd get away with it just - poor adhesion no doubt. eSun PLA+ been using for years. 

These are photos of the same print repeated. When i start the printer I get the awful one. I mess around with z calibrations (the judder at the top one) and print again and get it either super perfect or sometimes a bit iffy but not bad. Leave the printer a bit, start a new print and its terrible again. I'm thinking it's super pinda temperature sensitivity now but I thought super pinda was more reliable. z offset is -1.5 and the mesh isn't terrible.

RE: More Z offset problems

Is the PINDA secure in its holder? I'd give the screw that secures it an extra turn. If that doesn't help, then I'd consider a faulty sensor as an explanation.

RE: More Z offset problems

Yes,pinda is secure.  I contacted support and it looks like it could be a faulty heat bed not heating evenly. I do have a workaround now which is to modify the G code to heat the bed to 90 and then allow it to cool to the target temperature, giving the heatbed enough time to spread the heat evenly. Prints are coming out good again.

RE: More Z offset problems

OK, I found a workaround for this which I've been getting away with for 7 months. I make sure the bed is heated for a a good 5 minutes before I start printing. I did this by setting bed temp to 90c then let it cool to target temp before printing. However print quality is starting to deteriorate again a little and now I find I need 10-20 minutes of bed heating for the everything to print nicely.

I've done the "alcohol on the bed and watch how it evaporates" test to see if there's uneven heating but it seems fine. So is it some kind of warping?

The test which shows that it is purely down to extended bed heating is that I print 5 1 layer squares and then all come out great if I have the bed heated 20 mins first, then a normal print and the ones on the right hand side are great with the others looking like the pictures.

4 squares in 4 corners after 20 minutes they all look like the lower one, if I don't leave it 20 mins the ones on the left look like the upper one 

I print a round in the middle, again like the lower if I leave it 20 mins, like the upper if I don't wait

Help much appreciated again.

RE: More Z offset problems

Borrow an IR thermometer and point it at the bed.. record about 9 points at 2 minute intervals to characterize the bed on the top and it might show some anomaly.. This should show if the bed is heating within spec.. And if it isn’t the bed.. then you look at the heating of the hot end.

RE: More Z offset problems

Thanks - good suggestion. IR laser gun purchased from Amazon. Bed heated to 60c and left a few minutes. 9 point temperature measured as follows. Seems a fair bit under and as I thought it's particularly down in the bottom left. Guess I could just add 10c to accomodate. I don't suppose you've tested your bed as I imagine most have discrepancies. I'm sure the gun isn't 10c out by the way. If anything my first checks made me think it was slightly under reading.

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I should take my own advice more often.. grin.. On my bed my right side is cold.. and I've noticed this in prints.. not sure if the heat bed is flawed, but something I need to take into account. I often supplement my adhesion with glue.. and I add 5 degrees C to all bed temps.. So my initial thought on the advice is that every machine is unique and you need to characterize yours.. So you have a corner that is slightly cooler.. so you might set your temps from 5 to 10 higher to get 60C at the top and I think this is common. The temp sensor on these machines is never at the top. Really you just find a temp that gives you the adhesion and performance you need and that is right for your machine. Prusa's will be similar but different brands are likely quite a bit different. Makes it a bit hard if you are expecting absolute temp values across machines and look at manufacturers recommendations.. 

So there are 3 temps listed in my pic at each dot.. the first number is the temp when the LCD screen shows the bed has reached the set temp (60C) from cold.  So generally my bed is within 7 deg (except right side) when the system thinks it has reached the target and stays relatively constant. The other numbers are about 3 minutes apart Even though my right side is cool, I don't notice a different first layer appearance (as if the z is not right) when I print a part there.. I compensate by adding glue stick.  So if the temps you showed happen as soon as your LCD indicates the bed is at temp, I'd think your bed is pretty normal. (and your gun will be within a degree C). You should not have to superheat to 90 and then cool down, I'd suspect there is something else at play.

My system is MK3S+ that is only 1 year old with a Prusa rough sheet, measured temp using Fluke 61 IR thermometer.

RE: More Z offset problems

Thanks - no wonder the Prusa support tech wasn't bothered by the readings I gave him. I'll add 5c and see how i get on thanks.