So you level your bed by telling the printer to go to "home", then you get out your paper,
and stick it under, and you think a paper's thickness is how far the bed needs to be below
the nozzle?
Well, I'm afraid you're wrong.
I know this has been done by other creators in the past but I wanted to make a simple
short video on this and only this, so that I can explain it as clearly as possible with
no fluff, and you can watch it, share it with your friends, and we can all start understanding
exactly how bed leveling works.
Let's start by drawing stuff. Here's a representation of 3d printing, layer by layer. The hotend
has the nozzle on the end and the nozzle spits out a pre-determined amount of molten filament
based on the layer height and line width you have specified.
At the end of every layer it raises the hotend and thus the nozzle by exactly the line height,
and I can prove it in a moment, and repeats the process.
The slicer programs the extrusion rate to extrude enough filament, in the very basic
sense, to fill a rectangle around the height of your layer height setting, and around the
width of your line width setting. If you want to know more about that I have an accompanying
video that will be released around the same time as this which has some...interesting
revelations on that, but let's not get distracted.
The first layer is no different, and I can prove that too. The first layer extrudes exactly
the same amount as every other layer. So, we can see on this end on diagram how that
plays out.
Now the reason you're leveling wrong is because the first layer is just a normal layer. It's
no higher than the second layer. So why would you have the print bed anywhere else but literally
zero with respect to where the printer thinks z=0 is.
If you home the printer, and then use a piece of paper or card or whatever to space the
bed, what are you getting? This.
And because I like to back up my assertions with evidence, here's some Gcode generated
by cura for a simple cuboid, you'll get the same answer from prusaslicer too. If you see
the code here for a layer height of 0.2mm, the first thing the slicer has told the printer
to do, after the start code and purge line, is move up to Z=0.2mm and from then on you
can see there are no more Z move commands. The whole layer is being extruded with the
nozzle at exactly one layer height.
And layer two, same thing, yes I know, it's base zero so layer 1 is called layer zero
and the second layer is layer 1, but see here, the Z0.4 command.
And then layer 3 called layer 2 here, Z0.6, it's pretty obvious when you think about it
isn't it. But the point is there's no mystery offsets here. When you say you want a 0.2
layer height, you get it, right from the start. So that, is exactly how you should calibrate
your print bed unless you are doing something weird you should have it so that the surface
of the bed sits at z=0. It's literally that simple.
So what do you need to do? You have a couple of options, but if you want to use a known
thickness then you need to home the printer, THEN you need to go into your controls and
raise the printer by the thickness of your piece of paper. And then, this is actually
important too, you need to actually use the printer's controls to navigate across the
bed. If you do it by hand you have the servos turned off, and this will allow the z axis
to sag while you're moving it.
Your second option is to do it by eye, which is more the method I use. Home the printer,
turn off the motors, calibrate with paper, and it's important to note that the reason
I use paper is just to stop the nozzle scratching the bed, and also heat your nozzle up so it
will wipe the filament off the end while you do this. Then just do around a quarter turn
up on each corner when you finish, which seems to be around the right amount for one slice
of paper. Of course you're not going to be super accurate doing this, not even close
usually, but that's why you then have to manually level on the fly.
See the card for this template and the video on how to use it, but if your part isn't super
critical then you can also create a brim wide enough to do it by eye before the part starts
printing.
You could use a z-offset in the firmware or the start code when manually leveling but
I don't really like that option, so I won't cover it, if you're doing that then you probably
already know what you're doing.
The final option is to install auto bed leveling but that's a discussion for another time.
Now as to whether a normal squish is enough for the first layer, that's also a discussion
for another time, but I think now you hopefully understand how this process works, you can
make a more informed decision of how you want to do that.
If you like this kind of thing, then this is exactly my kind of thing, so please subscribe,
and I will see you in the next one!