UVTools Z Off-set/shift against Layers compression

[Darior78]

Is there a way to shift up a print adding empty layers, or with super short exposure time, at the beginning of a print in order to compensate for the initial compressed prints?
The new Elegoos with the "auto levelling" crap, do not allow for Z Off-set anymore and I guess this might be an issue with other printers as well.

[sn4k3]

How's the auto leveling failing?

The new elegoo printers have a manual z calibration (eg: Saturn 4 ultra). However, I don't know more about it.

With UVtools you can produce start black layers, by cloning the first layer and set it to all black. Each layer will shift by your layer height value.

If you want to automate you must create a script which does what you want

[Darior78]

I have a Mars 5 (non ultra) and modifed the build plate with adjustable thumbscrews and the plate is perfectly levelled.
What happens is that the "self levelling" function keeps lowering the plate to the same "pressure" and squeezing the print by 0.4mm. The printer keeps pushing the build plate to the same "pressure" even if I lift the build plate with the thumbscrews.

I did as you suggested and it worked wonderfully!
Thanks a lot!!!

[sn4k3]

Keep in mind that you might need to adjust Bottom layer count, if you adding many it may cure your first real layer at normal exposure...
Here a script you can use under File -> Terminal (Adjust only the offsetLayerCount):
Run once and close the dialog.

// Number of black layers to insert
byte offsetLayerCount = 4;

// Don't Touch
using (var dummyMat = SlicerFile.CreateMatWithDummyPixelFromLayer(0))
{
    var newLayer = new Layer(dummyMat, SlicerFile)
    {
        ExposureTime = 0.01f
    };
    newLayer.SetNoDelays();
    SlicerFile.InsertRange(0, newLayer.Clone(offsetLayerCount));
    SlicerFile.BottomLayerCount += offsetLayerCount;
}

[Darior78]

This is Gold!

Mil vezes obrigado!

[Darior78]

Keep in mind that you might need to adjust Bottom layer count, if you adding many it may cure your first real layer at normal exposure... Here a script you can use under File -> Terminal (Adjust only the offsetLayerCount): Run once and close the dialog.

// Number of black layers to insert
byte offsetLayerCount = 4;

// Don't Touch
using (var dummyMat = SlicerFile.CreateMatWithDummyPixelFromLayer(0))
{
    var newLayer = new Layer(dummyMat, SlicerFile)
    {
        ExposureTime = 0.01f
    };
    newLayer.SetNoDelays();
    SlicerFile.InsertRange(0, newLayer.Clone(offsetLayerCount));
    SlicerFile.BottomLayerCount += offsetLayerCount;
}

I tried the script and compared with the manual clone method as follows:

• Original 60 layers UVTools reports 6.0mm and print measures 5.7mm
• manually cloned 3 layers (0 to 2) and applied a black mask for the first 3 layers -> 63 layers UVTools reports 6.2mm total eight and print measures 6.0mm
• script with offsetLayerCount = 3 -> 63 layers UVTools reports 6.4mm total eight and print measures 6.2mm

I'll later try also with offsetLayerCount = 1 -> 61 layers UVTools reports 6.2mm
For the moment I'll stick with the manual clone method.

[Chainsoroth]

It's not a leveling issue... Just add "Wait before print" time...
See https://www.reddit.com/r/ElegooSaturn/comments/1i3bzr8/psa_increase_rest_time_after_retract_saturn_4/
and https://blog.honzamrazek.cz/2022/01/prints-not-sticking-to-the-build-plate-layer-separation-rough-surface-on-a-resin-printer-resin-viscosity-the-common-denominator/ for further information and about why it's happening and what you can do about it.

[Darior78]

I'm already using Honzamrazek's guides and have 15sec wait time before exposure for bottom layers basically addressing also elefant foot issue and general sharpness.
My issue was the print being 0.3mm shorter on Z axes and I've a specific need to address it.
On my Mars 2P/3P ans Saturn 8k, with GCode interpreter, I run a simple Z offset code to fix the squishing. The Mars 5 (non Ultra) doesn't have GCode interpreter and the "autoleveling function" keeps on lowering the build plate until the pressure sensor is triggered and there's nothing I can do excpet using UVTool with Tiago's script.

[Chainsoroth]

huh, very interesting. Sorry for the confusion/misinterpretation on my side.
That's a really odd problem, because the z-axis is due to the nature of the print technology also not very prone of inaccuracies due to shrinkage.
And I guess you had to print the file flat on the bed and couldn't lift it with supports right?

Does the squish happen in all four corners of your build plate? To me that sounds a bit like the problems I had on my old Mars 1 with a slightly misaligned/crooked build plate.

[sn4k3]

I don't know if the @Darior78 case is, but these printers have springs on platform, if the VAT have an offset and printer is squishing against the VAT the springs will compress, then it homes, when build goes up the springs start to return to normal position which cause build plate to be pushed against VAT and stay at 0mm position until the spring is fully relaxed, causing a loss of x layers and potential deformed print.