This may be a purely academic question unless I ever wanted to try a first layer thinner than 0.25mm, but…
The Velleman pdf for calibration says to adjust the clearance between the nozzle and bed to equal “exactly” 0.25 mm. I do this by using a deck of playing cards that happen to be 0.25mm thick. (each card).
So, the first layer can never be less than 0.25 mm thick, right? Is this number canned in the firmware configuration.h file someplace? I know that Slic3r allows you to specify the first layer independent of other layers, but if you want to make the first layer less than 0.25mm (who knows why) is that even possible? Would it require a firmware change? I mean, when Z-Axis home is commanded, doesn’t slic3R and/or firmware need to know what that means in terms of the distance between the bed and the nozzle?
For example, if I specified a first layer of 0.40 mm, the z axis must be commanded to move 0.15 mm, not 0.25. Where is this 0.25mm offset stored in slic3r and/or the firmware?
Art
The ideal clearance between the nozzle and bed is ZERO.
In practice you set a cold clearance that reduces when hot, then tweak your Z-stop to get a good first layer. It’s important to have your extruder calibrated first.
Slic3r has a Z-offset setting, so you could set your Z-stop 5mm above the bed and use a -5mm offset. That’s ideal for use with a proximity sensor for bed probing.
Paul, there is something about this that I just don’t understand. Slic3r allows me to set a first layer width. What command does it send if I ask for a first layer width of 0.25 mm versus 0.4 mm? If I had an initial gap of zero, then would it move the Z-axis 25 mm? If my initial gap is 0.25 mm, then the first layer would be 0.25 + 0.25 = 0.50mm, instead of the 0.25 that I asked for.
Vellermen (in the instructions pdf) says to set the gap to EXACTLY 0.25 mm, not zero.
The idea that the ideal gap =0 does not make sense to me because I don’t understand how slic3r behaves. For all but the first layer, slic3r can simply advance the Z axis by the amount specified for the layer thickness. But to command the thickness of the first layer, doesn’t slic3r (or the firmware) need to know what my initial gap really is?
If the ideal gap =0, why do the Velleman instructions say to set it to EXACTLY .25mm? If the ideal gap is 0.25 mm, then there will always be a 0.25 mm error in my first layer thickness. Slic3r must send SOME command for first layer thickness, otherwise if I set the gap to zero as you suggest, then the extrusion width is impossible to predict.
Art
In an ideal world, your build bed would be perfectly flat and level. The Z axis would home the print head so the hot-end nozzle was touching the bed and then when you start the print, the nozzle would be raised by the specified first layer height.
Because the bed is not perfectly flat, or level, there has to be some gap.
To cope with this gap, Slic3r allows you to extrude extra material for the first layer (and others in fact). The width of extrusion is based on the nozzle size, layer height and filament feed rate. By extruding enough extra material, you may get a varying width of extrusion as the bed gap varies, but you get a consistent thickness on which to build your next layer.
Most people are using a smaller gap than 0.25mm. A piece of 60gsm printer paper is roughly 0.1mm and is used by many. I’m using a length of 0.003" (0.076mm) shim steel.
Unless you have auto bed probing/compensation you tend to end up tweaking the Z stop most days to get a nice quality first layer that sticks to the bed.
It’s worth reading the Slic3r flow claculations; manual.slic3r.org/advanced/flow-math
Paul,
I understand what you said. Let me ask my question in a different way.
Does slic3r move the z-axis before printing the first layer? If not, than why does it need to know the first layer height/? If itdoes move the z-axis, then by what amount?
Thanks and Regards,
Art
[quote=“artcominio”]Does slic3r move the z-axis before printing the first layer? [/quote]Yes.
[quote]If it does move the z-axis, then by what amount?[/quote]The specified first layer height.
Paul,
I’ve been printing on glass with a 60 degree bed and no brim. Sometimes I had to wait for the glass to cool to remove the print, even small ones. I remember grabbing a 20 MM calibration cube and shaking the whole table without it breaking off!
Today I reduced my z-gap to paper thin from the Velleman recommended 0.25 mm. Nothing I printed would stick long to the glass! The first layer was too fat, and curled up ruining the print.
I never did understand the paper thin gap thing, so I’m going back to what worked for me.
Art