confused about 3d print export

[maker9876]

Performing some calibration tests on my 3d printer, extruded a 15 * 10mm rectangle 25mm and added 3mm fillets on the vertical corners. Exported as .stl using the "high" setting.

After printing a few of these (see photo below) noticed that the top and bottom 4mm of the parts were different, as evidenced by the vertical resonance lines on the prints. Took some head scratching to figure out this might not be the machine, nor the slicer but the .stl export itself. Indeed in the export dialogue there are 6 layers of approximately 4mm in the preview mesh. Was quite surprised that the "layers" might be different in the .stl export given that each one is materially identical. Confirmation was definitive when changed the aspect ratio on the export to produce significantly more layers and the "problem" went away (see the part on the left in the photo).

Would anyone like to explain what is going on?

Is there a detailed guide to .stl export?

Should I stop trusting the "high" setting and just crank everything to maximum resolution in the "custom" dialogue?

All suggestions welcome!

exported on high settingright hand part produced on "high" setting of .stl export

[maker9876]

One day later - guess I'm not the only one who doesn't know anything about meshing! 😉

[davebYYPCU]

No I can’t say what is going on.

I can only ask how did the one on the left come about,

far better quality, but no explanation of where it came from,

was it a custom Fusion or slicer setting?

[maker9876]

I'm printing at quite high speed (perimeters at 100mm/s) and adjusting parameters on the printer. But both were printed with exactly the same settings. The only difference with the one on the left is that I dragged the "aspect ratio" setting in the .stl export dialogue to create many more horizontal "Layers" in the mesh than were being generated on the "high" setting which is the one in the screenshot above. So the .stl are not identical and print differently, despite the fact that the object is the same all the way from bottom to top.

[davebYYPCU]

Ok, thanks, I can understand the difference now between the two, I have always stuck to high in Fusion, will have to test the Custom myself, as it is far better.

[Anonymous]

@maker9876  Hi I think the difference is the Initial Layer of your printer. Some 3D printers will add an Initial Layer to the design, and that will increase the height of the project. The M3D+ entry level printer will do that. The bottom layer will also be affected by the material used on the print bed. For example a Kapton Sheet on a heated bed can generate mirror like bottom layer. So the bottom and the top of the project will usually look a bit different. I think you should measure the height of your project to confirm that. You might want to use a Raft on your project and try to peel the raft off but the bottom will always look different. Kapton sheet is good, but if the project stuck on it and you try to take off with tools it could damage the Kapton Sheet. I suggest using Blue Tape on heat bed. They are reasonably priced and easy to replace. Just replace the damaged strips. If your printer really added an initial layer on your project you should consult the manual on the initial layer height and adjust your design accordingly. The fill density will also give you more dense walls and better looking bottom layer.

That is based on my experience on various printers I am using to make Food Grade PET Plastic Molds. I attached a picture here to show the difference. 

The Top model is printed by the M3D+ printer. An Initial Layer had been added and really looking bad.

The bottom left and right models are two commercial Food Grade PET Cookie molds made in Craftbot Plus Printers.

The left one is printed on Eurocel Blue Tape on 80C heated bed. The bottom right one is printed on Kapton Sheet at 80C. The bottom right one has mirror finish. The Craftbot Plus does not add an extra Initial layer in addition to the original design.

I hope that might give you an idea of what is going on.

[etfrench]

Stl export doesn't add any layers nor determine the height of any layer.  Your slicer program does that. 

Looking at the bottoms of the print, the left has noticeably more fill which seems to indicate a thicker first layer was specified.

Attach your Fusion 360 file and the stls for further analysis.

[maker9876]

Hi

Here's a link to the F360 file.

https://a360.co/2RUGu8A

The thing is to export the .stl 

a) on a "high" setting;

b) on the "high" setting but with the "Aspect Ratio" altered so that there are more layers in the MESH (not the print!!!).

The point and question revolves around the fact that this creates different results when printed. When use the word "layer" in original question am referring to the Mesh, not to the layers in the FFF print. If one looks at the resonance waves in the FFF print (the vertical lines) one can see that they are different towards the top and the bottom of the print (right hand object) and that those differences correspond to the top and bottom MESH "layers" when the export is performed on the "High" setting.

Have attached the .stl files from two different exports and this is what the Mesh looks like when the Aspect Ratio is modified (creating more "layers" in the Mesh which went on to produce the "better" print from the perspective of the Resonance lines reflecting that the .stl are non-identical). The thing that confuses me is that the part in question is the same all the way from bottom to top and it's not obvious that the Mesh has to contain many layers in order to map that. Which is what the export routine on the "high" setting has assumed, otherwise it would have dealt with the part vertically in the way that it has dealt with the fillets, by producing a very fine mesh.

Aspect Modified (the rest as on standard "High" setting)