Layer height - line height vs width?

Hello,

I just assumed the "layer height" is the same thing as the the "thickness" of the extruded plastic. However, after studying the objects I have printed with my printer - many of the same shape with different layer height settings - now I wonder if they are two different thing.

It looks as if while the layer height can be changed by controlling the amount of plastic squeezed out by the extruder, which should be proportional to how much (long) of the filament is pushed, the (horizontal) thickness the line in each layer is predetermined by the size of the hot end nozzle.

The shape I have printed many times is relatively small - it's that oozebane-test shape from one of the calibration guide, like U shape (without rounded bottom). The top area of each "tower" is quite small - small enough for me to count the number of lines. What I have noticed is this number of lines does not change even when I change the layer height, while I can clearly see the layer height does change according to this setting.

Is my observation correct?

Thank you.

just read comments on g code after you slice part, there is answer to all your questions...

Wow.. I didn't know that these *.gcode files are just text files with g code instructions. Well, now I have said it like that, it's actually funny that how I didn't know that.

Anyway, so I checked the g code files. I've been trying to tune my printer with 0.2mm layer height with 0.4mm first layer. My printer has 0.5mm nozzle.

Here are the comments from the g code file:

; layer_height = 0.2
; perimeters = 3
; top_solid_layers = 6
; bottom_solid_layers = 6
; fill_density = 0.4
; perimeter_speed = 40
; infill_speed = 70
; travel_speed = 130
; nozzle_diameter = 0.5
; filament_diameter = 3
; extrusion_multiplier = 1
; perimeters extrusion width = 0.85mm
; infill extrusion width = 1.02mm
; solid infill extrusion width = 0.85mm
; top infill extrusion width = 0.85mm
; first layer extrusion width = 0.80mm

And, here are the same comments, after changing the layer height to 0.4mm while keeping all the other settings untouched:

; layer_height = 0.4
; perimeters = 3
; top_solid_layers = 6
; bottom_solid_layers = 6
; fill_density = 0.4
; perimeter_speed = 40
; infill_speed = 70
; travel_speed = 130
; nozzle_diameter = 0.5
; filament_diameter = 3
; extrusion_multiplier = 1
; perimeters extrusion width = 0.53mm
; infill extrusion width = 0.53mm
; solid infill extrusion width = 0.53mm
; top infill extrusion width = 0.53mm
; first layer extrusion width = 0.80mm

So, it looks like I was half right - the extrusion width does not get smaller when I reduce the extrusion height. I was wrong, however, with my suspicion that the extrusion width would stay the same (a constant value predetermined by the nozzle size); it actually changes with layer height, but to the other way.

I wonder if the extruder simply isn't incapable of controlling the volume of the extrudsion to the degree of precision needed to change the layer height.

For example, it can't squeeze out just enough amount of plastic to reduce the extrusion height from 0.4mm to 0.2mm with keeping the width the same - there's some left over with 0.2mm extrusion height, and it gets rid of the excess by making the extrusion width wider..?

So, I checked the g code of other layer height settings to confirm this theory... And the conclusion is... "maybe?" LOL One thing for sure, there's something going on beyond my comprehension...

layer height                   0.1     0.2     0.3     0.4     0.5
---------------------------------------------------------------------
perimeters extrusion width     0.85mm  0.85mm  0.70mm  0.53mm  0.53mm 
infill extrusion width         1.98mm  1.02mm  0.70mm  0.53mm  0.53mm 
solid infill extrusion width   0.85mm  0.85mm  0.70mm  0.53mm  0.53mm 
top infill extrusion width     0.85mm  0.85mm  0.70mm  0.53mm  0.53mm

Besides not seeing a simple and obvious pattern between extrusion width and the layer (extrusion) height - other than the fact that when one goes down the other "may" go up in "some degree" - I don't know why the infill extrusion width becomes so big from 0.2 mm layer height and down. That's really puzzling that I can't even make up some kind of half decent explanation... Maybe Slic3r is trying to reduce the printing time for me, knowing it would take too long to print otherwise now that I am using a thinner layer setting (= more layers to put down)?


Anyway, if this is expected behavior (= it's not some faulty configuration/settings on my part), I may conclude the following (please feel free to correct me if I am wrong):

1. Reducing the layer height does not necessarily give me more accuracy. I may achieve higher accuracy vertically thanks to the thinner extrusion (finer layer height), but I may lose some horizontally due to the wider extrusion.

I don't necessarily trust my "experiment".. Since I have to redo the z end setup between every single print, and readjust the bed level every other day for some reason, I can rarely print the same object twice with the same quality even when I keep all the settings unchanged...

Having said that, this theory (gaining vertical accuracy while losing horizontal accuracy with lower layer height) actually is consistent with some of the shapes I've been playing with - I printed nuts and bolts with two different layer settings, 0.2mm and 0.4mm, and while the print with 0.2mm looks smoother and more accurate, but when I try them (put the bolt through the nut), 0.4mm layer ones worked better. 0.2mm layer nuts and bolts still fit each other and I can screw them on and off, but they wobble so much (loose fit) that sometime they skip a step when I screw them on and off.

2. The only way to actually increase the overall accuracy (both horizontal and vertical) is to use a smaller nozzle. Well, maybe not really the "only" way, but probably the most obvious one? Assuming the printer is tuned to the (near) perfection, other than changing the nozzle size, only other thing I can think of to help increase the accuracy is using belts with smaller steps...

3. Reducing the layer height by half won't increase the printing time by factor of 2 or 4. Since there are fewer lines to put down on each layer (now that the extrusion width is thicker), printing time per each layer would actually be smaller with smaller layer height. But not by a factor of 2, so the overall printing time is still bigger (but not by factor of 2).


Also, after these findings (some of which may very well be wrong/incorrect), now I am wondering if I should go back to 0.4mm layer height settings. Or find some fractional height between 0.4mm and 0.3mm, which does not result in wider extrusion width. I'm thinking that will be the optimal setup for my particular printer (esp the nozzle diameter) - the best vertical accuracy without sacrificing horizontal one and printing speed.

What do you think?

I'm pretty sure that you are limited by the maximum cross section of filament you can extrude. Not sure how slicer is doing the calculations but the maximum theoretical extrusion width for a 0.5mm nozzle is 0.2 square mm. In reality I think it is even a little smaller as the filament shrinks as it comes out of the extruder. If you calculate the areas of the extrusions in your table (assuming the extrusion is eliptoidal), the maximum is 0.21 square mm.

It seems that you could control these areas a bit by moving the print head faster or slower but looking at your numbers this does not appear to be the case.

KDog

Man, I feel so stupid.

I've learned that I can actually control this extrusion width.. .simply by setting those values in Slic3r. Slic3r indeed changed the extrusion width when I changed the layer height automatically, but I can overwrite that with manual value... duh.

Now with the manual settings I no longer get wide/fat lines with lower layer height, I am trying to tune my printer (yet again) for lower layer height.

I heard/knew about this constant, never ending tuning and calibration before going in, but it still is a lot of labor. Yesterday one of my friends asked me what I have been doing/printing with my new printer, and it was then when I realized I've been printing nothing but calibration object like 90% of time. LOL

Anyway, I slap on my own wrist not reading Slic3r manual inside out before posting a dumb question like this. Sorry about that.

Hello Yamster,

Why are you making 6 top and bottom solid layers? That is way overkill, I believe the default is 3.

NormandC Wrote:
-------------------------------------------------------
> Hello Yamster,
>
> Why are you making 6 top and bottom solid layers?
> That is way overkill, I believe the default is 3.


Oh yes, it was a bit of overkill. LOL I was just experimenting with different configurations, and it seems like I took those comments from the g code files when I had 6 solid top layer setting. I've changed it back to 3 already.