Generating STL files

[NigelHay]

I've been getting sample parts 3D printed (currently with the FormLabs Form 2 printer) to see if the quality is good enough for us to consider investing in a system. The samples are not yet good enough but the printer re-seller is saying that this is partly due to the STL file generated by Inventor. My main problem is that the large cylindrical surface shown in the attached file comes out looking like it is made as a series of flats instead of a smooth surface. My first sample was made with the default Inv settings, resolution = Brep. I have sent another STL file generated at high resolution but I am told that this still shows facets instead of a smooth surface. Can anyone suggest the best settings to get a smooth cylindrical surface?

[mcgyvr]

How big are your parts dimensionally?

I use the "high" setting and circles are circles for me..

Most of my parts are 4x4x4 inches or smaller..

That is the setting you should be looking at.. High "should" be good enough for most typical 3d printed parts.. 

[NigelHay]

The part is about 70mm diameter x 25mm. Attached image shows the problem.

[mcgyvr]

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@NigelHay wrote:

The part is about 70mm diameter x 25mm. Attached image shows the problem.

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That image is from the brep right? That was your problem..

Use high and all will be fine...

[JDMather]

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@NigelHay wrote:

... My first sample was made with the default Inv settings, resolution = Brep.

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Create simple cylinder.ipt file.  (or your actual *.ipt file)

Export to stl with high resolution.

Attach the two files here.

[Frederick_Law]

Yes, don't use brep.

The circle is 30mm OD.

[johnsonshiue]

Hi Nigel,

Another way to prove it is not Inventor related is to simply take STL Export out of the equation. Does the 3D printer supply a tool to handle mesh? Does the printer take files (STEP or SAT) other than STL or OBJ? If yes, you can simply send the printing software or the printer the Brep file and see how the print turns out. I suspect it is more with the printing resolution than the geometry generated from Inventor.

Many thanks!

[NigelHay]

.ipt & high res STL attached. The part external face is a simple revolution, in preview when creating the STL it looks OK.

[NigelHay]

Yes, the image was the Brep version but I sent a high res file to the print company & they said it still looks faceted. Should have the physical part in a day or two.

[JDMather · Accepted solution]

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@NigelHay wrote:

... but I sent a high res file to the print company & they said it still looks faceted. Should have the physical part in a day or two.

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Settings can be changed to increase the mesh density, but it should be understood that there are no curves in an stl file.

The geometry is converted to planar faceted triangles.  The more facets, the closer the representation to curves, but there will still be planar facets.

[Frederick_Law]

STL looks good.

CURA slice as circle.

If part still have straight edge, you should use another printer.

[mcgyvr]

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@NigelHay wrote:

Yes, the image was the Brep version but I sent a high res file to the print company & they said it still looks faceted. Should have the physical part in a day or two.

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Ad JD said there are not "round" features in an STL file.. Its always composed of facets to approximate a round..

"HIGH" quality will be much better compared to Brep in this regard..

Here is how your part looks now in my 3d printer software..

You can still see the facets but its far better than what you had before..

[NigelHay]

Thanks for that. Another printer maybe but the point of this exercise is to see if the sort of printer that is in our price range is up to the job. I'm waiting for the sample from the high res STL to arrive then we will make a judgement.

[Frederick_Law]

In that case find another 3D printer or dealer.

If the part don't come out round, either something wrong with their software or hardware.

Or whoever doing the printing don't know what they're doing.

[JDMather]

It should also be noted that the shaded cosmetic  "pretty pictures" presented by the slicing software is not a technique for judging what the print output will look like.

[Frederick_Law]

BREP slice:

High:

[NigelHay]

I got the parts from the high res files & they are substantially better. The faceting has almost disappeared & the finish is much improved. Still not quite good enough for our purposes but close.

[n.schotten]

Well... STL is a faceted format. You won't get perfect circles.

Only the detail level during export will determine how fine the facets will be.

From there it's on the slicer to either folow the facets or make a guess that you actualy want a circle/arc.

And then ofcouse, lastly, is the quality of the printer and if it is acurate and smooth enough to make circles/arcs.