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bed levelling question

Andyfife
(@andyfife)
Distinguished Member

I have a question about bed levelling and the use of the squares.  I have an Anycubic Mega Zero 2.0.   I watched the videos about be levelling and downloaded the squares. I sliced using Cura.   

I ran the print and the center square appeared to print okay. (more about this later).  The printer then attempted to print the square at the back right.  The filament pulled off the bed, stuck to the extruder and made a bit of a ball of filament.  I aborted the print and cleaned the extruder. 

I then relevelled the bed ( I thought) and tried the print again. [I used a piece of paper to manually level].   When the printer tried to print the center square, it did the same as the back right from the first attempt - filament gobbed onto the extruder.  Aborted the print again. 

I re-watched the video on the use of the squares.  After examining the center square that did print, it was lines and not holding together.  So, this means the head was too far from the bed surface.  When I levelled between the first and second attempt, I am pretty sure I lowered the bed instead of raised it, which would make the extruder father away on the second attempt than the first. 

Long story but my question is : If the extruder is too far from the bed surface, does it create the small separate lines when you examine it ( as in the center square from first attempt) AND cause the filament to lift off the surface and glob the extruder (as in the back right square in the first attempt and the center square in the second attempt)?   It seems when I try to print small items, the extruder more often than not, will grab the filament and lift it off the surface causing the glob.  

Ken

Quote
Topic starter Posted : 20/09/2021 10:05 pm
Pablo
(@placherre)
Member Moderator

Hi Ken!

Don’t worry, I will guide you with some steps in order to adjust the correct bed levelling.

First, I am going to show a picture with how a levelled printer should look like by looking at the first layer:

First Layer Pattern

What is happening to you is pretty much similar to the middle pattern, correct? Where the nozzle is too far from the bed and the filament is not bonding correctly between segments and to the bed. Therefore, the first layer will come out from the bed when the nozzle passes and touches that layer that is trying to print.

When doing the bed levelling, did you check only in the 4 corners or also check the centre of the bed? Also, did you level the bed with the bed and nozzle at working temperature? For instance, if you are using PLA, the bed should be at 55°C and nozzle close to 200°C (make sure to retract some filament in order to avoid oozing). This will also affect your levelling, due to a heat expansion of the components. 

Also, when you are levelling, do you make several passes around the corners until you don’t have to turn any knob? Manual bed levelling is an iterative process, where you have to repeat the steps until you manage to achieve a good level. 

Moreover, I suggest you check if the bed is warped. If you try to level the four corners and the middle of the build plate, the gap is the same in all five points? If not, the bed might bend on the sides. Another way of checking is by using a steel ruler if you have one. Place the ruler in the middle of the build plate (using the straight edge) and look at the gap between the edge and the centre of the bed. try to do this in the X and Y directions to verify how warped might be. If the gap is too small, you can use a flashlight and light the back of the ruler. If the bed is warped, you will see light between the ruler and the build plate. The following picture will give an idea in how to place the ruler and the light source

Warped Bed Ruler Check

Would you send me some pictures if you have the chance to check the build plate with the ruler?

If the bed is warped, you can compensate for the difference by printing a very thick first layer. It is recommended not to exceed the maximum layer height, which is 75% of the nozzle diameter. For example, if you are using a 0.4 mm diameter nozzle, the layer height shouldn’t exceed 0.3 mm. What slicer are you using? So I can guide you how to set up this first layer height. Another option is to level your build plate in a smaller area, instead of the outermost corners. For example, if the model has 100x100 mm sides, you can level the bed near the centre, taking 50 mm to each side, making a 100x100 mm square. One last resource you can use to compensate for a warped build plate is to use rafts. The counterpart of using a raft is that the printing time will increase and more filament will be used. 

Finally, verify the nozzle and the bed are both clean. When cleaning the nozzle, I recommend you heat it up close to 200°C and use a metallic brush to remove any debris left. Remember to retract some filament to avoid oozing.

Would you also reply to me about the material and printing temperatures for the bed and nozzle you are setting up? 

I am looking forward to your response.

Kind regards,

Pablo

ReplyQuote
Posted : 21/09/2021 9:06 pm
Andyfife
(@andyfife)
Distinguished Member

@placherre

Pablo,

I am using Cura for a slicer, Ecco-PLA for filament.  My settings are 190c and bed @ 60c.   I do heat both up before levelling. 

My printer is the Anycubic mega pro 2.0.  It has the feature to "level corners" which I use.  It does not level the center of the bed though.  After doing the 4 corners, I run it around again, until I don't have to adjust any settings.  I usually use paper although I also have feeler gauges but not sure which one would be best.   I don't have a metal ruler unfortunately, but when I tried using a heavy plastic one, shining a light behind, it did not appear there were gaps. 

The slicer, Cura, is set for an initial layer of 2mm.  

20210921 145928
20210921 154748

(tiny image - hope you can see it)

This was one of my prints.  The first is as they were on the bed.  The second once I took them off.  As you can see, they are stringy and not all there.  So this is bed and nozzle too far away, correct?  

After having the trouble with the prints above, I levelled again, much closer, and the corners appeared to be in one piece but quite thin.  When you hold them up to a light, you can see the light through them.   Also the center square stuck to the bed so well, that I had difficulty removing it and had to scrape it off. This is the image of the four corners only.   The second image shows how thin the squares are but they do hold together. 

20210922 145256
20210922 150812

 I am wondering if the Ecco-PLA be part of my issue.  With some other prints I did, it appeared to require a much smaller gap than regular PLA.  I am going to change to a different filament and see if the issue persists.  I will let you know the outcome. 

Thanks so much for the 'hand holding'.   It is really appreciated. 

Ken

ReplyQuote
Topic starter Posted : 22/09/2021 10:17 pm
Pablo
(@placherre)
Member Moderator

Hi Ken! 

Thank you for your reply and the pictures. I can see them pretty well.

Taking a closer look at the first picture (with the squares still on the bed) I can notice that the centre one and the one on the back left corner look very similar. Adding to the test you made with the ruler, I can say that the bed is not warped. Also, looking at the damaged square (the one on the right hand side) I can notice it has pretty much the same surface as the other two. 

But, when I see the second picture, the pattern indicates that the nozzle is still a little bit high. On the contrary, on the third and fourth pictures I can notice that the nozzle is too close to the bed. Due to the thickness of the squares (shown better on the fourth picture). Therefore, you are right in the middle of the ideal nozzle-to-bed distance… 😀 

Posted by: @andyfife

The slicer, Cura, is set for an initial layer of 2mm. 

I was wondering if you tried to write 0.2 mm instead. Because it would make much more sense to your actual situation based on the pictures you shared.

Posted by: @andyfife

My printer is the Anycubic mega pro 2.0.  It has the feature to "level corners" which I use.  It does not level the center of the bed though.  After doing the 4 corners, I run it around again, until I don't have to adjust any settings. 

Sorry, I wasn't clear when I refer to levelling closer to the centre of the build plate. What I wanted to describe (if the bed is warped) is that you can level the bed using the four knobs underneath, but in a square closer to the centre. Instead of levelling over the knobs (for instance) you could measure 50 mm to each side from the centre of the build plate and then level those four points using the knobs.

Since you have feeler gauges, I would recommend you to try with them, they are much more accurate that paper. Especially because paper may have variations on its thickness. Normally, in our houses we have 80 gsm (grams per square meter) paper, which is about 0.065 and 0.11 mm thick, depending on the manufacturer. Therefore, you could start using the 0.1 mm (0.004”) gauge. Anyways, compare it with the paper you normally use for your bed levelling.

Finally, since you have issues with this particular PLA brand, I suggest you adjust some of the settings. Because filament composition and characteristics change among manufacturers. Also, you should adjust another set of settings for different colours of the same brand.  I would start with 55°C on the build plate and 195°C or 200°C on the nozzle. I would increase the nozzle temperature in order to create a better bond between the filament and the bed. Also, I would drop the build plate temperature in order to move from the Glass Transition Temperature (GT). In a nutshell, GT is the temperature that changes the molecular structure (in this case of the PLA) and the material starts to be more flexible than rigid. For PLA, this temperature is close to 60-65°C depending on the composition. 

In addition to the setting adjustments, what is the printing speed for the first layer? Normally, this value should be 40% of the normal printing speed. In Cura, you can find this setting under Speed > Initial Layer Speed > Initial Layer Print Speed. Remember to activate the Expert mode in order to visualize this setting. In the following picture I am showing you as reference where it is located.

First Layer Print Speed   Cura

I am looking forward to seeing the outcome of your tests.

Kind regards,

Pablo

ReplyQuote
Posted : 23/09/2021 2:27 pm
Andyfife
(@andyfife)
Distinguished Member

Pablo,

Sorry for not getting back to you sooner. I made the changes you suggested, up the temp to 195 and lower bed to 55.  I am (now) printing the initial layer at 0.2. It was at 0.1.  Speed for initial layer is25mm/sec and others are 40mm/sec

I leveled using the 0.1 feeler gauge, and the photo is the outcome.  Three of the squares are perfect!.   The one which was back right on the bed pulled off the one border which caused the really rough edge. As it was printing, I raised the bed just a bit and the print for the rest of the square worked out. 

The one square printed okay, but it has bumps on it, and I am not sure what caused those ?  Could be dirt or oil on the bed?

But generally, I am very happy with the outcome. Thank you so much for helping me out. 

Ken

squares

 

ReplyQuote
Topic starter Posted : 29/09/2021 6:51 pm
Andyfife
(@andyfife)
Distinguished Member

Update:

I cleaned the bed a bit and reprinted the squares.  I think they look pretty good!!

Ken

squares2

 

ReplyQuote
Topic starter Posted : 29/09/2021 7:08 pm
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