Understanding Z-value/ problem with the powdered metal sheet

Understanding Z-value/ problem with the powdered metal sheet  

Active Member


I'm testing the original PRUSA "Sheet steel TXT" and have massive problems printing the first layer. The first layer calibration looks fine, but the adhesion is near zero. The original sheet prints fine without any issues. So therefore I have two questions:

1) is it possible to calculate the Z-Value for the powdered sheet if you have a good value for the original sheet? IMHO this should be possible due the magnetic sensor and all the difference  should be in the thickness of the powdered structure regardless the thickness-difference of both sheets.

2) Is there any slicer settings for different sheet structures? IMHO this should be because different structures requiring different volume amount.

I've attached an image showing the bad first layer on the left side (powdered sheet), and the good one on the right side (standard sheet). In the left image you can see big gaps between infill lines. Gcode for both print is the same, but different calibration Z-values.

Any help would be appreciated,

thanks in advance

This topic was modified 1 year ago by johann
Posted : 13/09/2019 8:11 pm
Honorable Member

need to crank your live Z down a bunch on  the PC sheet - probably -.200mm or more from the smooth PEI sheet

Posted : 13/09/2019 9:54 pm
Active Member

If I do this, I loose the homogenous infill structure at least during first layer calibration.  -960 is a good value for smooth PEI, going deeper than -140 (-1100)  using the PC sheet brings massive problems. I'm just wondering why there is only one first-layer calibration procedure, for the PC sheet the flow-rate should be significant different...

Posted : 13/09/2019 10:31 pm
Honorable Member

version 3.8.0 firmware supports live Z calibrations for 8 sheets

the PC sheets are much thinner than the smooth ones and there is variation on the PC sheets as the PC process has variation

Posted : 14/09/2019 12:05 am
Active Member

oh, thank you, that's one of the information I was looking for, at the moment I'm using firmware 3.7.2. So I will upgrade and see if hopefully the results are getting better.

Posted : 14/09/2019 7:20 am
Active Member

I upgraded to 3.8.0 and did a bunch of calibration series, but the results are still the same. To summarize, the PC sheet doesn't stick, at least not for PLA, maybe better for PETG. In contrast, the smooth sheet works very, very well!

Posted : 14/09/2019 8:22 am
Veteran Member Moderator

NOTE, I only print PLA, PETG and TPU... so I don't offer surface suggestions for more exotic filaments!

the textured powder coated build sheets seem to have a slippery surface when new, 

whether this is part of the production process or whether we run our fingers across the surface to admire the texture and deposit finger grease, is unknown. 

there are many argumentative threads about what is correct and what is not.    and like the bible, or any rule book, people will select the sentence or sentences that suit their particular view, and try to publicly humiliate or bully other with different beliefs and understandings. 

so please take this information in the spirit of support, that is intended, or leave it  however you feel appropriate. if you have different beliefs, pass on your solution and let the reader make up their own mind...

With MY textured sheets, (I have 4 of them),   I  choose to lift them off the printer (One at a time! Lol), take them into the kitchen, rest them on a clean water resistant cutting board, (to prevent damge by over flexing) and squirt a small amount of Dish Wash detergent (Soap) onto the surface of the build plate, then I use a clean, fresh, dish-wash sponge with some water, to work the detergent into the pores of the textured surface 'on  one side only'   then, taking care not to bend the flexible build plate, I vigorously rub the sponge back and forth, first in circles, then diagonally, then longitudinally, then laterally (Basically every which way you can think of...)  with the intent of dissolving and removing any surface residue. then still using the sponge, and fresh water (as hot as my hands can stand) I rinse the build surface, free of all bubbles, finishing with just hot water rinse and then I dry the build surface with clean plain paper towels, ensuring not to touche the build surface with my fingers...    having ensured the back of the build plate is also dry, I put the build plate straight onto the printer heat bed, ensuring that I don't touch the top surface, and that nothing is trapped between the heatbed and the build plate, then I immediately heat the heatbed using the appropriate preheat setting on the printer LCD Menu. and proceed with my next print... 

I don't wash the underside of the build plate, unless it gets exceptionally greasy....    so far, I have never used the second side of any textured plate or any smooth pei sticker plate ( I am saving them for when I wear out the first side... )   (One of my Sticker plates is getting close to being turned over, after MANY hours of printing...) 

(My Mk2 printer PEI Sticker lasted  a couple of years. until I upgraded to the Mk2.5, type 52, 12volt heatbed with removeable  build plate...   and the only damage was on the purge line area, where the PEI got worn out, so I put a length of Kapton tape along the purge line area to prevent further damage, and there was a tiny tear in the main print area where a friend, was not as careful as Me, and knocked the PEI with a spatula... 

with PLA, I have tried :-

raising the heatbed temperature...   for big prints I use up to 70C... 

Glue stick...   and found no benefit that outweighs the mess of removing it.

Hairspray... no benefit 

Blue painters tape... -works but the edges of the tape can get stuck in the print surface and removing tape and reapplying is a pain... 

ABS juice...  Messy, smelly, nasty,  and the Acetone used, to remove the ABS Juice tends to crack PEI Stickers... so it probably also damages Textured powder coated surfaces...  as a completely different subject I had grease on my powder coated motorcycle wheel rim, I wiped it off with Acetone, and that one wipe, was enough to damage the paint surface!   

PVA glue (thinned with water)...     works but leaves a residue, which is a pain to remove from the build plate

Magigoo and other proprietary grunges,..   never tried them,  feel free to experiment if you find the need...

Now I just use soap and water... 

IF there are smear marks, on your build plate surface... it is NOT CLEAN... 

these prints are PLA, tiny surface contact area and stick with no further surface preparation, other than cleaning the build plate...   

with TPU and PETG,  especially on PEI Stickered build plates I use either:-

Talcum Powder  (rubbed well into the surface and all of the loose powder dusted off! )  (Yes there is a small chance of inhaling powder...   but I suspect most of us have survived having our bottoms powdered as babies, and many of us will have used scented powder after baths and showers)

Finger grease, if the part to print is small, I literally just rub my fingers across the centre of the build plate where the model will be printed, and along the intro / purge strip area where the printer deposits the initial prime material. this is usually enough to promote easy removal.
If it's a bigger print, you can recharge your finger grease by wiping your fingers across your forehead...  (this is not a good idea if you are wearing makeup... (I rarely wear makeup when 3D printing, the printer doesn't care what I look like!!! :-D))

again I have tried gluestick, PVA etc, and don't bother anymore...   

IF your Print does not want to let go, of the build plate surface,  drip some IPA around the base of the print (on a cold build plate) let it soak for a couple of minutes, and try lifting the print again, it should release more easily... 

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...
Posted : 14/09/2019 12:06 pm
Active Member

joantabb thank you for your detailed experience, I agree with all of your statements, I'm also into 3D printing several years. Nevertheless, the PC sheet is in comparison to the smooth one very less sticky. As the day goes by, I realize the adhesion is getting somewhat better. So my theory is, brand-new sheets are coated  with whatever substance and the adhesion will better the more cleaning cycles are passed through. Anyway, I'm sure my calibration process is OK and if interested, you can see how dramatic the difference is the structure between the two sheets viewed from a microscope.  Thank you all for your contribution, and happy printing.

Posted : 14/09/2019 5:21 pm

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