Real First Layer Height
I have 4 printers (One PRUSA and three other types) now, so I do manage with this, but I'm going to throw this question out because I've never really understood it.
So the question, how does the Live Z-height set on the MK2.5/3 react with the "First Layer Height" setting in Slic3R on the "Print Settings" tab in the "Layer" section? This setting can be a mm value or a percentage.
Are these two settings added together to get the "real" first layer height? Is the slicer setting just ignored?
On other printers, I level the bed with knobs and a 0.2mm feeler gauge say, but every other slicer also seems to have a "first layer" setting. I never touch this setting, and printers always seem to print at this manually adjusted first layer height, not the slicer setting.
So why do slicers ask for "first layer height" when they never seem to use it, or do they?
Thanks.
RE: Real First Layer Height
When you adjust Live-Z, you're adding or subtracting a small amount of height from the 0 position of your Z axis to get a good 1st layer. The sequence is:
- Startup gcode homes the printer to establish the X=0, Y=0 & Z=0 position of the extruder.
- A slicer generated command moves the extruder up to the layer height you specify for your 1st layer and starts extruding.
Unfortunately, the Z=0 position may be sub-optimal for a number of reasons, including:
- We want a bit more or less squish for some filaments for adhesion purposes.
- We have a hard time gauging the thickness (but thanks to Jeff Jordan's amazing "Life Adjust" procedure, this is much easier.)
- Your print surface may not be perfectly flat.
Live-Z lets us add or subtract a small increment from that 0 position to make these adjustments. On your other printers, you may be doing a manual 1st layer adjustment that does something similar, only more manually.
Slicers do use the 1st height setting and will try to generate gcode to produce layers of that height. Live-Z adjusts the 0 position up or down slightly and independently of your slicer. Ideally, setting a 0.2mm 1st layer height in your slicer will result in a 0.2mm layer height being printed, but it can vary.
Mesh bed leveling further complicates all this (for our benefit) by making yet further adjustments at various spots on the bed to compensate for an uneven print surface.
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RE: Real First Layer Height
Just to add to Bob's excellent explanation, many printers do not have a minimum first layer height and allow the nozzle to touch the build plate. Because the PR build plate is PEI (a meltable plastic), the PR firmware does not allow the nozzle to get closer than 0.15mm to the bed.
Imagine that the slicer does not have a "first layer height" setting and that you wanted to print at 0.05mm layers. On the PR printers, the first 3 layers would be printed at a height of 0.15mm, the minimum allowed.
Even with other printers, when printing at 0.05mm layers, you will get a much better stick to the bed if the first layer is set to 0.2mm.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
RE: Real First Layer Height
[...] Because the PR build plate is PEI (a meltable plastic), the PR firmware does not allow the nozzle to get closer than 0.15mm to the bed.
Is the 0.15mm offset official? I had encountered it, but didn't want to confuse anybody with it. I did see a "soft endstop" or some such message flash up in Pronterface at one time.
It does sounds like a "use a minimum 0.15mm 1st layer" advisory might be worthwhile. Thanks for the info!
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He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Real First Layer Height
// Travel limits after homing
#define X_MAX_POS 255
#define X_MIN_POS 0
#define Y_MAX_POS 212.5
#define Y_MIN_POS -4 //orig -4
#define Z_MAX_POS 210
#define Z_MIN_POS 0.15
But be aware that the PEI can still be damaged if the nozzle is left at that height for too long in one place (as I did when testing the effects of the print fan on a Mk2 - right in the middle of the bed at 250 degrees) 🙁
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
RE: Real First Layer Height
Yes. From Configuration_prusa.h
[...]But be aware that the PEI can still be damaged if the nozzle is left at that height for too long in one place (as I did when testing the effects of the print fan on a Mk2 - right in the middle of the bed at 250 degrees) 🙁
I also noticed dents in my PEI from hovering the nozzle at minimum while doing final heat-up, also at bed center. I now do my PINDA warmup at the rear edge of the PEI and raise the nozzle to 3mm before issuing the final nozzle temp command in startup gcode.
and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan
RE: Real First Layer Height
The Mk1 - with glass build plate - had a minimum Z of 0.2mm. I think that was because the printer was aimed at beginners and also because that printer was equipped with a Lite6 and the aluminium heat break would bend easily.
That was when I learned to compile the firmware to get a lower MIN-Z
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
RE: Real First Layer Height
@pjr
I am also new and trying to understand this.
The first layer height is determinend by the look and stickeness to the bed and so could be anything.
Now in my slicer i specify 0.1 mm layer height.
How am I sure that the total height of my (technical) object will be correct if the first layer height in the calibration isnt an exact value?
Bert
RE: Real First Layer Height
@bert-eding
Hi Bert,
I believe the Mk2.5 / mk3 firmware has a minimum Z height of 0.15mm>
Is your lowest feature at 0.1mm above the build plate? do you actually need that thin a first layer? can you guarantee that you will not get any warping that may destroy your model with such fine limits? maybe you should consider allowing thicker first layer to permit machining to size after cooling
As Peter mentioned he changed the firmware and re compiled it, to suit his needs. You may have to do the same!
your actual first layer height is a factor of expected layer height, Live Z adjustment, Printer Component tolerance, machine maintenance condition, Ambient temperature, print temperature and heatbed smoothness.
Your finished model dimensions are dependant upon similar issues. if you print the same model with different manufacturer's filament of the same type, or even different colours/rolls of the same manufacturers filament, you can end up with slightly different measurements.
3D printing is effectively using a computer controlled glue gun, to create articles in a lightly constrained volume. it's amazing at times what you can achieve, but you need to be wary of expecting too much.
if you print with different materials, you may have to scale the models to compensate for different shrinkage, ABS, for instance shrinks more than PLA under normal circumstances.
additional issues may add to inaccuracies, for example the Pinda Probe is affected by thermal tollerances, which may add to your dissatisfaction.
using a textured build plate may also induce unexpected variance. as the filament is deformed into a negative of the build plate texture.
regards Joan
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