Getting inconsistent 1st layer results between adjusting Z-level vs. changing first layer height
Based on the "math" of it, it would seem that increasing the negativity of the Live Z-level adjust by XX steps would be the same as decreasing the first layer Z-level (from the standard 0.2mm) by XX um (XX/1000 mm)
Similarly, decreasing the negativity of the Z-level adjust by XX steps would be the same as increasing the first layer Z-level (from the standard 0.2mm) by XX um (XX /1000mm)
However, while diretionally the changes are the same, the magnitudes of the change are very different. Specifically, changing the Z-level by XX steps plus/minus has a much more profound effect on the first layer than changing the first layer Z-level by XX/1000 mm.
Both give repeatable results.
What am I missing in my math or understanding of printer geometry?
Best Answer by EsotericMaker:
Mea Culpa. I realized I had a signe error in my script code that revised Z-levels.
So to summarize, everything works FINE -- i.e., for a single layer print, I get the same result by increasing/decreasing the NEGATIVITY of the Z-level adjust by XXX as by lowering/raising the Z-level in the Gcode by XXX/1000 mm
And thus the following are all equivalent:
- 1000 Units of Z-level live adjust
- 1 mm of Z-level adjust in GCode
- 1 mm on a feeler gauge
My apologies for leading you all on a wild-good chase...
RE: Getting inconsistent 1st layer results between adjusting Z-level vs. changing first layer height
Just to clarify I am not changing the first layer height in the slicer but rather directly adjusting the Z-level in the resulting G-code. Since this is a single layer, rectangular print (basically a Z-level test pattern), there is just a single Z-level change for the entire interior area. Mathematically/geometrically, adjusting the Z-level at the beginning of the infill should be equivalent to manually adjusting the Live Z-level at that point of the print (other than the units)... but that's not what I am getting...
RE: Getting inconsistent 1st layer results between adjusting Z-level vs. changing first layer height
Based on https://forum.prusa3d.com/forum/english-forum-general-discussion-announcements-and-releases/measured-correlation-between-layer-height-first-layer-calibration-and-bed-level-correction/ , I suspect the problem is that 1 Z-level unit is not 1um.
It would be good to know the actual conversion number and even better to know what it is actually measuring and how it affects the processed GCode...
Where the layer is extruded depends on the calibration.The thickness of each layer is a function of the quantity of filament extruded - as long as it is low enough to squish together,
Cheerio,
RE: Getting inconsistent 1st layer results between adjusting Z-level vs. changing first layer height
I'm sorry but not sure how this answers my question... both casea are identical except for difference in Live Adjust-Z in one and the Z-level in the other. They should effectively have the same Z-level, hence the same thickness, hence the same extrusion.
RE: Getting inconsistent 1st layer results between adjusting Z-level vs. changing first layer height
One thing that will most probably screw up you experiment is the software end stop of your MK3 at z=0.15. Regardless of the gcode fed into the printer it will never go lower than that.
Next thing to consider is that you will have under extrusion in the next higher layer after the one you tempered with because the nozzle will be higher above the previous layer and the extrusion rate will be to low.
Better use the live-z / first layer calibration to setup the printer to be at the correct z position (that’s what the first layer calibration does, making sure the nozzle is actually 0.2 mm above the bed when z=0.2) than to try to adjust the gcode for an incorrect z position.
If at first you don't succeed, skydiving is not for you.
Find out why this is pinned in the general section!
RE: Getting inconsistent 1st layer results between adjusting Z-level vs. changing first layer height
Based on https://forum.prusa3d.com/forum/english-forum-general-discussion-announcements-and-releases/measured-correlation-between-layer-height-first-layer-calibration-and-bed-level-correction/ , I suspect the problem is that 1 Z-level unit is not 1um.
It would be good to know the actual conversion number and even better to know what it is actually measuring and how it affects the processed GCode...
Well to the best of my measuring capabilities using a feeling gauge with 0.05mm minimal height, I showed that the following are all equivalent to within less than 0.05 mm
- 1000 Units of Z-level live adjust
- 1 mm on a feeler gauge
- 1 mm of Z-adjust on the Prusa keypad
- 1 mm of GCODE from the Octoprint terminal
So, indeed 1 Z-level live unit = 1um to within a couple percent.
So the mystery remains...
RE:
One thing that will most probably screw up you experiment is the software end stop of your MK3 at z=0.15. Regardless of the gcode fed into the printer it will never go lower than that.
Next thing to consider is that you will have under extrusion in the next higher layer after the one you tempered with because the nozzle will be higher above the previous layer and the extrusion rate will be to low.
Better use the live-z / first layer calibration to setup the printer to be at the correct z position (that’s what the first layer calibration does, making sure the nozzle is actually 0.2 mm above the bed when z=0.2) than to try to adjust the gcode for an incorrect z position.
- My range was actually 0.16mm to 2.4mm
- I printed only a single level
I am not using this to print real objects, just to play around with Z-level adjustment on single layer test prints... and understand what is going on at a very granular level
RE: Getting inconsistent 1st layer results between adjusting Z-level vs. changing first layer height
Mea Culpa. I realized I had a signe error in my script code that revised Z-levels.
So to summarize, everything works FINE -- i.e., for a single layer print, I get the same result by increasing/decreasing the NEGATIVITY of the Z-level adjust by XXX as by lowering/raising the Z-level in the Gcode by XXX/1000 mm
And thus the following are all equivalent:
- 1000 Units of Z-level live adjust
- 1 mm of Z-level adjust in GCode
- 1 mm on a feeler gauge
My apologies for leading you all on a wild-good chase...
RE: Getting inconsistent 1st layer results between adjusting Z-level vs. changing first layer height
Another thing that can affect the first layer is how level the bed is. There are mods to improve the bed level. I also saw a video on how the bed level changes as it heats up. When I did the silicone mod to my printer, I tested this and found that I needed to level my bed while it was hot to be consistent when printing. I went from 0.5mm of errors to less than 0.1mm in the centre of my bed but found my bed is not flat using this test. Accurate enough for 99% of printing. I now do a preheat before any print job.