Behavior of the first layer

[AntonO]

I have recently found something strange to me. When I manually regulate the height of the first layer (using "First layer settings") and make it very small I get a huge under extrusion in g-code preview.




In reality I get exactly the same behavior. Printing with 100% I get under extrusion and it can be solved by increasing height to 200%.
From my previous experience I remember that adjusting the build plate too high (nozzle is too low), I got just more squished layer (no under extrusion).
Is it some specific behavior of Simplify3D? Why it does it? Or it is a usual behavior for printing too low?

[CompoundCarl]

That doesn't happen to me. Are you sure you aren't looking at the infill for the part?

Maybe post your factory file so that others can help more

[AntonO]

You can actually see that layer is colored in green color, what actually corresponds to Solid layer.
It is the link to factory file https://drive.google.com/file/d/0BwLRxx ... sp=sharing
I hope somebody has an explanation, because I can not figure it out.

[parallyze]

Not really an explanation - but what kind of nozzle are you using? If it's a 0,35 or 0,40 nozzle then 200% layer height at 0,20 layer thickness is not within the recommended ratio (typically layer height is a maximum of 80% of the nozzle diameter). The flashforge dreamer seems to come with 0,4 nozzles equipped, so layer height shouldn't be higher than 0,32mm - you should get a warning when slicing with those parameters, do you?

I can see the same thing happen when using a first layer height of 50%, 30% and 20% as shown in this picture:

But honestly - printing 20% of 0,2mm layer height equals to a first layer of 0,04mm and I wonder if that's even possible with the printers usually seen*. I wouldn't be wondered if there's some kind of calculation going on while slicing that just has to make the lines thinner or so (width/height ratio, nozzle/width ratio and so on).

bye,
para

[CompoundCarl]

Oh, I think I see what the difference is. As you print that layer thinner and thinner, it gets so close to the bed that visually the 2 things start to overlap. If you just toggle the "Build table" option on the left side of the preview, you can see that it's still the correct width, but as others mentioned, you are just printing it so thin it is getting really close to the table.

So it's still printing correctly, but it's just getting really close to the table.

[AntonO]

Thank you guys!
Okay, it explains why we see such a weird behavior in g-code preview. But it doesn't explain why I actually get the under extrusion when I print it. When I print on 100% for First layer height I get exactly the same as in g-code preview (under extrusion). When I rise it to 200% no under extrusion, but layer becomes too high and you can see it visually, what irritates me quite a lot. Some ideas guys?

[dorsai3d]

Probably just have your nozzle just a little too high above the bed. Use the global g-code offsets to lower it down (try -0.05mm steps) and you'll probably get better results.

[parallyze]

I'm not sure if the g code preview shows underextrusion.

This is the first layer at 20% (0,20mm regular layer height) shown from the side:

This is the same view with a first layer height of 80%:

As you can see the preview always draws preview lines with a certain "thickness". I'd say it's just the way it is shown which may lead to think it's underextrusion. But if a layer is only 0,04mm (like it's the case with 20%) the preview somehow has to display this properly - hence the first layer
is drawn a bit lower.

Anyways, the first layer shouldn't be considered a good source for detecting over-/underextrusion. Especially when printing small stuff like shown in your screenshot. Apart from how level the bed is and minor changes while heating/cooling down the nozzle and heated bed, one might think it's overextruding but in reality the overlap is too much (just an example). So you get too much material at the point where the inner shell and the infill meet. This material is then dragged by the nozzle to a certain amount while it's moving on doing it's infill lines.

But when printing a bigger surface using the exact same settings you might notice that albeit having these "ridges" at the infill/shell borders, the center of your object looks like it's underextruding. Hard to explain and I don't have any pictures at hand to show this, sorry. Get the first layer to stick properly and then go on with calibration. It needs a certain amount of layers to really tell if you're over- or underextruding. And avoid extreme values while calibrating. If, let's say, you need to push overlap to 50% because else the infill and shell won't touch each other, then something else is going wrong.

Try to stay in the range of layers between 0,2 - 0,3 for calibration, especially on the first layer this will make things much easier. And it's a good range for a 0,4mm nozzle. And don't forget about your extruder gears - depending on the setup your extruders might not be able to output such small amounts of material reliably (0,04mm layer height is really, really tricky).

[dkightley]

I'm not sure if the g code preview shows underextrusion.

The preview doesn't show "underextrusion" for the first layer as a different colour, thickness, etc , as there is actually no underextrusion.

As a first layer height under 100% results in the amount of plastic being extruded not being reduced, the simulation draws the layer height as the same as if it was 100%, but...and an important but...the simulated layer is drawn at a lower height so that the top is at the reduced height. The layer is consequently drawn part above the bed....and part below the bed.

One point to take into consideration.......if you have any global z-axis offset, this will move the whole model up or down, causing additional confusion!!!!

[parallyze]

I'm not sure if the g code preview shows underextrusion.

The preview doesn't show "underextrusion" for the first layer as a different colour, thickness, etc , as there is actually no underextrusion.

As a first layer height under 100% results in the amount of plastic being extruded not being reduced, the simulation draws the layer height as the same as if it was 100%, but...and an important but...the simulated layer is drawn at a lower height so that the top is at the reduced height. The layer is consequently drawn part above the bed....and part below the bed.

One point to take into consideration.......if you have any global z-axis offset, this will move the whole model up or down, causing additional confusion!!!!

So where's the difference to what i wrote?

As you can see the preview always draws preview lines with a certain "thickness". I'd say it's just the way it is shown which may lead to think it's underextrusion. But if a layer is only 0,04mm (like it's the case with 20%) the preview somehow has to display this properly - hence the first layer
is drawn a bit lower.