MakerGear Forum

I have a 20x20x5mm high thin wall box (sides only). I print it with 1 layer thickness in ABS with a 2% expansion/contraction allowance in S3D.

My S3D settings are:

Extruder:
=======
Extrusion width: 0.55mm
Extrusion multiplier: 0.9 (I will try change this later to get perfect fill once I have X/Y/Z sizes correct.
Infill: 0%

Layer:
=====
Layer height: 0.1mm
Top solid layers: 0
Bottom solid layers: 0
Outside/Perimeter Shells: 1

S3D slices it with layers 0 to 52. That means 53 layers. I don't know why it uses 53 layers ?!? With a layer thickness of 0.1mm, it should use 50 layers !

Part final sizes are: 20.4 x 20.4 x 5.27mm .... so pretty darn close. If I change the extrusion multiplier or extrusion width, I can get it down to 20.0x X,Y

I tried adding a Z-axis offset of -0.1mm, but that made no difference.

I cannot figure out how to get the Z height correct! It always adds 2 extra layers, it seems! Any ideas how to fix this ?

a couple things that i can think of that will affect this. the bed gap or z-stop bolt adjustment. there will be a little variance here depending on where that is set. in s3d you also have your first layer height adjustment. if this is anything other than 100% that will adjust where the layers fall then the top layer will need to round up a little. what you have going on there is probably just a couple small things but they are totaling up in the end. this may or may not be the problem. its just what i can think of off the top of my head.

jimc wrote:a couple things that i can think of that will affect this. the bed gap or z-stop bolt adjustment. there will be a little variance here depending on where that is set. in s3d you also have your first layer height adjustment. if this is anything other than 100% that will adjust where the layers fall then the top layer will need to round up a little. what you have going on there is probably just a couple small things but they are totaling up in the end. this may or may not be the problem. its just what i can think of off the top of my head.

The bed gap is 0.15mm when cold with feeler gauge as the light on the Z-stop is triggered. I measured it hot too (> 90deg bed temp) and there was no real difference in feel with the same gauge.

I had the first layer set to 90% (default in S3D), so I have changed it to 100% and the extrusion multiplier to 1.0 and now the Z-height of the finished part is 5.4 mm .... GRRR !!!!!

Then I remembered that I had added 2% to the scale of the part, so I set that back to 100% and did another print... same BS...

I guess I don't understand how S3D takes a 5mm high part and slices it with 0.1mm layers and gets 53 layers ... then prints a part that is 5.3mm high.... so I went looking in the G-Code file.

The GUI in S3D is saying layers 0 to 52 .... But the Gcode says:
; layer 1, Z = 0.1
...
; layer 51, Z = 5.1
... so, 50 layers and 5.0 mm of Z travel as expected!!

So now I am even more confused as to why my part is too high ......

Bed gap will affect the physical height of your part in reality, but not in S3D.

Maybe your model is ever so slightly off?

I just generated a 20x20x5 cube in OpenSCAD ("cube([20, 20, 5]);") and sliced it with 0.1mm layers. The last layer (before "layer end") says: which is correct (not 5.1, that would give you a 5.1mm cube).

Calibration file that I am using is attached.... It should be 5mm high.

Also attached, the gcode file I mentioned.

Same thing. Last layer shows:
When you rotate the object into printing position, then double click the model, does it show z=0 under minimum coordinates?

Attach your factory file (File->Save Factory File).

Also, as an unrelated note, your model is just the exterior faces only and is non-manifold. In this case, it doesn't seem to matter, but what you want is a fully solid object printed with the same print settings. That will get you a thin wall box just the same.

jsc wrote:When you rotate the object into printing position, then double click the model, does it show z=0 under minimum coordinates?
Attach your factory file (File->Save Factory File).

Also, as an unrelated note, your model is just the exterior faces only and is non-manifold. In this case, it doesn't seem to matter, but what you want is a fully solid object printed with the same print settings. That will get you a thin wall box just the same.

Yes, it shows z=0 and object height = 5mm. Factory file attached. Note that I added a Z-Axis offset of -0.10 as the bed is 0.15mm off the nozzle tip when cold (using feeler gauge).

The geometry is non-manifold. I just want a single layer around the outside, so I can get extrusion width and multiplier correct (btw, what does everyone else get?).

Incidentally, what should the skirt look like ? A single smeared layer, or all 4 outlines as separate threads ?

1st layer should not be smeared or seperate threads. Really what you should have are single extrusions where the edges touch making one solid piece

jimc wrote:1st layer should not be smeared or seperate threads. Really what you should have are single extrusions where the edges touch making one solid piece

OK.. I am getting separate threads at the moment. To me, this means that the extrusion width is thinner than S3D thinks it should be. But I have set it correctly, based on a single layer thickness box... so how do I 'fix' this ?

Mind wrote: To me, this means that the extrusion width is thinner than S3D thinks it should be. But I have set it correctly, based on a single layer thickness box...

The distance between the nozzle and platform is about twice as large as you expect.

Your settings tell the extruder to emit enough plastic to fill a 0.55 x 0.10 mm "rectangular" thread. If the platform is 0.2 mm from the nozzle, that same amount of plastic will produce a 0.27 x 0.20 mm "square" thread. The adjacent threads will be 0.55 mm on center, leaving a 0.23 mm gap on each side.

That's what makes printing with 0.10 mm thick layers so challenging: an initial Z error of +0.10 mm produces separate threads (with zero adhesion) and an error of -0.10 mm produces a smear (and clogs the nozzle).

Start with 0.20 mm layers, measure the actual thickness, and adjust the Z offset to get exactly 0.20 mm. Adjust the alignment until it's the same across the entire platform, then go back to 0.10 mm and see how much better it works...