CAD Forum

I am trying to export a circular part to .stl for 3D printing. What I've found is that .stl geometry is formed by polygons, which gives a surface that is polygon shaped, not circular (closer to being a stop sign than a circle). Since the 3D printer will attempt to produce whatever geometry it is given, this results in a noncircular part.

Is there any way to produce a circular part in .stl (or .obj)? I already understand that I can crank up the resolution in .stl to improve the stop sign effect, but this doesn't eliminate it.

Thanks in advance for your suggestions.

I've had this problem before, I got a cylinder that was supposed to seal against a plunger/o-ring and there were about 20 faces that made up the interior surface of the cylinder. As you can imagine, the o-ring didn't seal at all.

System Options -> Export Adjusting these options to a finer (smaller) value will yield more facets making your part more circular. Be careful though, increasing this seems to exponentially increase the exported file size.

Good luck!

Uncle_Hairball wrote: ↑Fri Sep 23, 2022 2:55 pm Is there any way to produce a circular part in .stl (or .obj)?

Nope, STL is millions of triangles, period.
Make the mesh as small as possible. Billions triangles.

Depends on your printer and slicer.
Some slicer can convert segments to arc.
Some printer can use arc G-code.

Alex and Frederick, thanks for your advice. I've tried everything, but have come to the conclusion that there is no other way. Lots of triangles (which take a long time to generate) and live with the imperfection. Strange that the printer can't use real geometry like .step.

Hello Uncle_Hairball, (great name btw!)

I'm curious to see your model or what is still not smoothing? Can you share/show the file?

but yeah, cranking up the poly count or deviation/angle is pretty much the only option within SolidWorks.

Otherwise, you can use over software (Rhino3D, Blender,..) which could give you increased smoothing options, like sub-D.

Or, you can also try bumping up the Anti-Alias options in your Slicer software.

zxys001 wrote: ↑Sat Sep 24, 2022 2:07 pm Hello Uncle_Hairball, (great name btw!)

I'm curious to see your model or what is still not smoothing? Can you share/show the file?

Yeah, I'm curious too if you can share. I have access to a few different processing programs for our Stratasys printers so they may behave a bit differently as well for processing.

AlexB wrote: ↑Mon Sep 26, 2022 10:13 am Yeah, I'm curious too if you can share. I have access to a few different processing programs for our Stratasys printers so they may behave a bit differently as well for processing.

Here's a defeatured model you can look at. I greatly reduced the deviation and angle tolerances to decrease the size of the flats, but they're still there.

You settings should be like shown in the image. This is more than enough for even the higher end process... SLA, Polyet...etc.



Alternatively there is also (.3MF) which is "trying" to become the new standard universal file format for Additive Manufacturing. There are a ton of benefits that it has over the older file formats the challenge is that the slicing software for the printer has to be able to import it.

Uncle_Hairball wrote: ↑Mon Sep 26, 2022 12:59 pm Here's a defeatured model you can look at. I greatly reduced the deviation and angle tolerances to decrease the size of the flats, but they're still there.

Honestly, although you could increase it, that's actually not bad considering the 318mm part and 1.4mm perimeter facets.

zxys001 wrote: ↑Mon Sep 26, 2022 1:46 pm Honestly, although you could increase it, that's actually not bad considering the 318mm part and 1.4mm perimeter facets.

so, I just remade your part and the best I can get is ~1.3mm.

Gentlemen, I appreciate your efforts. It looks like it isn't possible to eliminate the facets, only make them smaller. I guess I can live with this; it just seems like it ought to be possible to make a circle. Thanks again.

Arthur NY wrote: ↑Mon Sep 26, 2022 1:38 pm You settings should be like shown in the image. This is more than enough for even the higher end process... SLA, Polyet...etc.



Alternatively there is also (.3MF) which is "trying" to become the new standard universal file format for Additive Manufacturing. There are a ton of benefits that it has over the older file formats the challenge is that the slicing software for the printer has to be able to import it.

Yes, I tried .3mf, but it has the same problem and took a very long time to export. It would add an additional step of processing through other software to convert to a format that the 3D printing software can read (.stl or .obj only).

Thanks for the suggestion!

There are free / demo versions of several other cad software. (NX, SE, F360 that I know of.) If this is a solidworks limitation, you could export the parasolid to one of the other platforms and then generate the stl/3mf from there.

(ETA: The facets aren't a solidworks problem, but it might be possible to make them smaller in other software.)

I ran it through the stratasys slicer we have and it seems to have a built in smoothing for faceted curves. It ended up making the faces into arcs. I can't really output it to any useful formats for you though...

What machine are you printing on that if you change the settings to like I showed, are still showing up in the physical model? That there are facets on the model is correct, that is what a mesh is. Even if it could take a (.step) file, which some slicers can do, it will still convert it to a mesh before creating the G-Code.

If you have images of the model printed after changing to the settings shown I'd like to see the results if it can be shared.

That is how 3D printing works. It will be polygons no matter what you do. It doesn't matter what CAD software you use if it is a polygonised file format like STL or 3MF. It is a legacy of the beginning of the technology in the 80s.

If you need a real circle not a polygon with 1000 faces you have to use a CNC.

HDS wrote: ↑Fri Sep 30, 2022 11:39 am That is how 3D printing works. It will be polygons no matter what you do. It doesn't matter what CAD software you use if it is a polygonised file format like STL or 3MF. It is a legacy of the beginning of the technology in the 80s.

If you need a real circle not a polygon with 1000 faces you have to use a CNC.

Not to 100% disagree with you on where you're going with this, but it is possible to get a very smooth surface with with various AM processes. Polyjet, SLA....etc. and very little to none shows in terms of facets. Some of what you can get for jewelry and lost wax casting is just mind blowing.

What he hasn't really outlined is where he's taking the model to when getting the model 3D printed.

Arthur NY wrote: ↑Mon Oct 03, 2022 6:54 pm Not to 100% disagree with you on where you're going with this, but it is possible to get a very smooth surface with with various AM processes. Polyjet, SLA....etc. and very little to none shows in terms of facets. Some of what you can get for jewelry and lost wax casting is just mind blowing.

What he hasn't really outlined is where he's taking the model to when getting the model 3D printed.

Well, not sure about what smoothing OBjet Studio has but yeah, there are ways to further smooth other tools like this freebie..
https://www.meshmixer.com

@zxys001 Yes, software like this is great in ways that it allows for smoothing to happen either globally or locally by using a brush. Which isn't something you can do upon export from most softwares. Some additional ones to take a look at are Blender, zBrush, 3D Coat, and Modo also have similar tools because AD has stopped all development of Meshmixer and knowing them they will pull even being able to download it once it's folded into Fusion 360.

Arthur NY wrote: ↑Mon Oct 03, 2022 6:54 pm Not to 100% disagree with you on where you're going with this, but it is possible to get a very smooth surface with with various AM processes. Polyjet, SLA....etc. and very little to none shows in terms of facets. Some of what you can get for jewelry and lost wax casting is just mind blowing.

What he hasn't really outlined is where he's taking the model to when getting the model 3D printed.

I don't disagree that you can get smooth surfaces from polygon models. With enough polygons the difference from a perfect circle will be smaller than the capability of the machine to make it. However, if the OP is looking for an actual circle (or cylinder) in the model it is not how polygon file format like STL or a process that uses those models work. I don't want them to keep trying to make grape juice out of apples. They have to accept the limitations of the process they chose.

You have to use surface or solid model like a STEP file and CAM software with a CNC machine if you want to see circles in the models or G-code. Even then if you want circles you have to program the tools paths and post the G-CODE that way.

Uncle_Hairball wrote: ↑Mon Sep 26, 2022 2:18 pm It would add an additional step of processing through other software to convert to a format that the 3D printing software can read (.stl or .obj only).

3D printer read G-Code.
Slicer read STL, OBJ, STEP and make G-Code for printer.

Which program do you use to create G-Code?
Which 3D printer are you using?

HDS wrote: ↑Wed Oct 05, 2022 8:38 am I don't disagree that you can get smooth surfaces from polygon models. With enough polygons the difference from a perfect circle will be smaller than the capability of the machine to make it. However, if the OP is looking for an actual circle (or cylinder) in the model it is not how polygon file format like STL or a process that uses those models work. I don't want them to keep trying to make grape juice out of apples. They have to accept the limitations of the process they chose.

You have to use surface or solid model like a STEP file and CAM software with a CNC machine if you want to see circles in the models or G-code. Even then if you want circles you have to program the tools paths and post the G-CODE that way.

Ok so the underlying thing about the way things are displayed on a computer, when it comes to circles for examples, are actually tiny lines that, to us, are imperceptible, to know the difference. Point in case, go into the image quality in the document properties and adjust the sliders down. You'll notice the same thing that happens when exporting out as a mesh is the same thing that is shown on the screen. So a circle can be made to look like a hexagon or if slide it things all the way to the right it will seem like it is a perfect circle. But it's not, it's just a series of tiny facets like a mesh.

The real question is which technology are the models being made with. Until that is answered then it's that much harder to figure out where things are not going well.

Thanks for all the input, gentlemen. I appreciate it.

I am using Solidworks to generate the .stl, Preform to prepare the print job, and a Formlabs 3L to print.

@Uncle_Hairball If you have the settings where I first indicated for both sliders then that's well beyond what the Formlabs is capable of achieving in terms of resolution.

If anything showing a screen shot of the model in Preform and the physical model to see the final results would be the next best step.