Theoretical first layout height vs. actual layer height
Hi everyone,
I assembled my first Prusa printer and am quite satisfied with the result. I just have some question: how important is the theoretical first layer height vs. the phyiscal layer height? As the provided method is really unsatisfying, I downloaded some G-Code to print only the first layer in a square. Then I measured the layer height using a quite precise Mitutoyo caliper. I found quite a significant difference of 0,2mm vs. 0,38mm in the physical result. So I adjusted my z-offset by 0,18mm and still the result is like 0,23-0,25mm. Using the first offset as achieved using on-board methods left me with me prints on the coated surface that would detach after a few layers. Using the second approach yielded quite good results, although I think they could still be improved.
Now my main question: how important is it to get the real height of the first layer correct?
I now get well adhersing prints, but I can see that something happens about 4mm from the bottom, as there is a visible line. Should I try to print something like a test cube and if I do - how do I use the results?
Here is an example of the first problem:
Link: https://photos.app.goo.gl/YQrHu9Kkm98mbT3D7
And furthermore I found a problem with the alignment of the bed itself:
Link: https://photos.app.goo.gl/N1stccapxRAsg47P9
In my opinion the left side is a little too deep for the nozzle, but the middle just looks perfect. As you know, bed leveling is done before every print, so this should not happen in my opinion. What can I do to minimize this problem?
Cheers and stay healthy,
Christian
RE: Theoretical first layout height vs. actual layer height
Hello Christian,
are you using 7x7 mesh bed levelling, or 3x3? (49 test points instead of 9 test points during bed levelling)
are you using a textured sheet or a smooth build sheet?
what do the top and bottom sides look like on your first layer test pieces?
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Theoretical first layout height vs. actual layer height
Line shift:
The line your pointing to, is often visible after a print, this is the floor of the benchy.
Possible to get better is print lower temp, or use more perimeters.
Could also be over extrusion, lower temp or adjust extrusion multiplier.
Check your belts if they are not to loose, also check the grub screw if is not loose.
RE: Theoretical first layout height vs. actual layer height
Make a temp tower to see what the best temperature is , then you get less stringing.
RE: Theoretical first layout height vs. actual layer height
@joantabb
I was not aware of 7x7 leveling, so I am using 3x3. I am printing on the textured sheet. I now reprinted the test sheet and it looks like this:
Bottom: https://photos.app.goo.gl/uW2S4BzEvzEpHUw69
Top: https://photos.app.goo.gl/t9Y3TyfM37zGdCt86
This now looks a little worse than my test print and I would raise the nozzle a little. If I measure the thickness, the smooth part comes to 0,26mm and the rough part is around 0,44mm. Measuring the rough part with calipers of course results in the maximum thickness, as they are measuring an area.
The whole thing is 75x75mm. Is it normal to have such a height difference in such a small area? Should I maybe try to loosen the heatbed bolts and try to retighten them? Maybe I put too much or too little torque on one of the bolts which causes the bed to warp.
I will also try to use the 7x7 calibration and see if this gives me a better result.
Thanks to the other replies - I will also start to fine tune the temperature. I am currently using the recommended 210°C with the original Prusa PLC. I checked the belts and grub screws but as far as I can tell they are fine.
RE: Theoretical first layout height vs. actual layer height
the ripples in part of the square suggest that your Live Z setting is too low (too large a negative number)...
the roughness is caused by the nozzle ploughing through the previously laid down filament and as it is a surface defect should not be considered for measurement purposes.
I suggest that you tune for best surface finish and then measure what you have achieves
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
RE: Theoretical first layout height vs. actual layer height
Search on youtube how to adjust the first layer, then you see examples.
If you go to low the model will not stick good to the bed and models will release during print.