Strange "biscuit" layer

Hello All…

I have been reading the forums and have learned a lot. I put my question in the “getting started” section as I am still very much a beginner.

I have been printing some parts and noticed that I was getting what I call a “biscuit” layer at the beginning of my prints.

I didn’t really mind as I was printing brackets but noticed those layers were really “bumpy” and it seemed like the nozzle dragged across it. So I reprinted another one and noticed about 20% or so into the print, extrusion seems very minimal and it really does look the head drags across the previously printed layers.

I also noticed that at times I would get the “print in air” issue (although not consistently).

Since I had the nozzle gouge the bed previously, I did the following to try and remedy the situation (not in order):

1- Replaced the removable print sheet
2- Replaced the hotend (added thermal paste to the thermistor per other posts even though I did not notice any temp. fluctuation on the hotend)
3- Realigned the proximity sensor per snapmaker recommendation
4- Performed extruder calibration
5- Performed bed levelling calibration (25 point).

You will see from the last picture that the print skirt looks squished on the right side despite the bed levelling and adjusting z offset (current at 0.15mm). I also just had the print in air happen again.

The only thing I can think of it that maybe my filament is bad? I have left it out (didn’t know about moisture). I have new ones but didn’t want to crack one open until I had checked everything else - especially since it does print after that “biscuit layer” is finished.

All printing is using the black PLA from snapmaker. Settings are 205 nozzle temp, 70 heated bed temp. As I am a beginner I am using Tinker CAD to create models (am looking at other platforms) and then Luban to import, slice and generate g code.

Thank you all for your time in reading this and I hope it is something easy :slight_smile:

Biscuit layer on final printed product

Picture of unloaded filament after recent “print in air” occurrence

I don’t know why this happens

For the “print in air”, how often does that happen? If just once or twice maybe you got unlucky and the filament got chewed up by the drive gear, any more often and there is probably something to fix.

For the “biscuit layer”, could you share what settings you are using in luban, as well as the gcode and STL files?

Hi Bobby - Thank you for taking to the time to respond.

The “print in air” happens at least 30% of the time - some times more but when it does happen it is always after that “dragging” layer as shown in my first post.

I have attached the zip file of the model I generated which contains the gcode generated by luban. Note I have recently printed another model for a completely different design and the same sequence occurs - “nozzle dragging layer”, “print in air”… will fail once or twice this way and will then print to completion but with the biscuit layer.

Base - (222.3 KB)

Does this also happen with other models? Your gcode looks fine to me, as does your model, so that is probably not the issue but I wanted to ask regardless. It does look like the bottom left of the skirt is extremely squished, suggesting that the nozzle is way too close to the bed in that area. You could try setting the z-offset .05-.1mm higher than you usually do to see if it helps, but I would be surprised if a bad initial offset is causing issues this far into the print.

If you are willing to try another slicer, I would recommend doing so in order to more confidently rule out Luban and your gcode as the issue. Cura and prusaslicer tend to be good options for people looking for something other than Luban.

Zooming in on the filament picture, that looks like there is a chunk missing at the top of the gear teeth marks. That usually means the extruder gear was unable to push filament through, so it tore a chunk out of the filament. Once that happens, it will have trouble printing, and usually just moves around the bed without extruding anything. It may or may not catch later and restart printing, but by that point there’s usually nothing to print on, so you end up with a ball of spaghetti.

There are 2 reasons that can happen: The nozzle is too close, and can’t push the filament out; or there is tension on the filament that prevents the extruder from pulling it in. You mentioned the squished side, so it could be too close. But that issue should mostly go away after the first layer. Keep an eye on the print, and see if you notice tension on the filament. The default spool location without an enclosure can cause some binding, and there are numerous filament guides and spool mounts for the v2 on thingiverse if you are having this issue.

Lastly, most people say the Snapmaker Black PLA is worthless. I haven’t used it, but there are many posts on the forum advising people to just throw it away and get a better class of filament.