Weekend Update 4/30/23

[Chris333]

Even in AutoCAD circles are 96 segments.

[jagged ben]

Even in AutoCAD circles are 96 segments.

That is false.

[Chris333]

It is in mine when you export the file. Open the file with something else and it is 96 segments. In AutoCAD while you are viewing it may change as you zoom, but I think that is to save memory or to make zoom faster.

[wazzou]

That is false.

I don't know one way or the other, but, please show your work.  Why is it false?

[Lemosteam]

Recall that any conversion of the native cad file can impact the geometry quality. Only files viewed in their native format will appear as designed in their native tool. All others must be considered reasonable facsimile thereof.

Also there are settings and conversion types, even within a given format, .stp files have several, .stl has several settings depending on the native tool exporting the original file.

Each transformation from the native file is ALWAYS a degradation from the file as created originally as each conversion must interpret from the previous file.

This is why I only prefer sending paid files as a direct conversion to .stl from Catia.

[jagged ben]

Well ok, in "professional" CAD programs, but most modelers use "CAD-lite" like SketchUp or TinkerCAD. In SketchUp circles are series of straight lines.

Good point.  I googled this on Sketchup and found out that you can change the number of segments it uses to draw the circle, apparently by object.  So if using Sketchup this would be a good place to check.

[jagged ben]

I don't know one way or the other, but, please show your work.  Why is it false?

I happen to be working in it today, so here's pics.  Hopefully the resolution isn't too truncated for you.
[ Guests cannot view attachments ]
[ Guests cannot view attachments ]

Edit: forum turned the second picture sideways.  It shows the right side of the top pic zoomed in, where you can see that if I draw in straight line segments at angles that Chris says define the circle,  the program still renders the circle as a curve outside the lines.

Sorry for thread hijack.

[jagged ben]

It is in mine when you export the file. Open the file with something else and it is 96 segments.

If a dwg file, then that's a limitation of whatever other program you're opening it in.  If another format, it may be a limitation of that format or a limitation of AutoCADs conversion algorithm.

 

In AutoCAD while you are viewing it may change as you zoom, but I think that is to save memory or to make zoom faster.

It takes more computing power, not less, to properly render the circle as you zoom.  And it takes more data, not less, to define a cirlce by 96 points instead of 3.  So that makes no real sense.  If they were trying to save computing resources, they would define the circle by three points but render it chunkily on screen until you wanted to plot.  Which is more like how AutoCAD behaved back when I first learned it over 30 years ago.  My classmates and I were all impressed with how smoothly the plotter drew curves.

[samusi01]

HEMTTs are looking great. Working on printing some out now, thank you for these.

Good to hear, let me know how they come out. If the 978s do well on a different printer, they’ll be next up.

[u18b]

I hope Aaron can get it worked out.  He's really doing some amazing work.

[Chris333]

In Cad you cannot click on a segment so that may be the wrong word. But imported into Sketchup you can click on each segment.

About the way AutoCAD renders a circle on screen. This on the left is a circle and the line on the right intercepts with it. The further I zoom in on it the more blocky the circle will look and here it is so blocky that it looks line the line is not touching the circle, but it is. Just a visual thing.

[Chris333]

Also in Sketchup a circle will have 24 segments unless you change it and you cannot go back and change it. You need to change it while making the circle. But an arch like the car roof might be will be 12 segments by default.

So if I make a boiler or curved roof I will make the out side circle a high number of segments so it will be smooth. But go too high and Sketchup will slow down. I found this out by drawing tiny rivets in AutoCAD and then importing to Sketchup. All of those tiny rivets had 96 segments and Sketchup would get real twitchy and slow.

[jagged ben]

Chris, if you type REGEN or change VIEWRES settings in AutoCAD that display behavior may change. 
And yes, definitely if you import AutoCAD files into SketchUp then the latter 'reinterprets' the content and you lose resolution on curves.

That said, all this really deserves its own thread in the 3d printing forum.  The broad point is, most design programs are to some degree not WYSIWYG  and understanding the difference at each step along the way between design and 3d print is key to troubleshooting.

[Chris333]

What if a wheel has 118 sides? 

http://www.douglas-self.com/MUSEUM/LOCOLOCO/polygon/polygon.htm

[chessie system fan]

Aaaannd I posted too soon.  Now that I'm home, I sprayed the new test car with primer.  The flat spots are still there.  The good news is they are barely perceptible. I couldn't even see them without paint, and now I don't see them unless light shines on them at a certain angle.  There's no point even posting a photo because it wouldn't be visible.

I've always used Fusion360. The exporting process has been the same throughout: I've just hit "export" and chosen the STL file type and that's it. The only slicing software I've tried is the Photon versions.

But there is a difference.  Back in the old Photon days, I created my passenger car roof profile with a control point spline from a car drawing in Mainline Modeler.  For those new ATSF cars I posted this week, I decided to be an  and created a new roof profile from the AAR dimensions so it would be completely accurate.  That required drawing the roof from differently sized circles.  I'm not sure why that would make a difference, but it did.

But now the plot thickens, because I went to my scrap drawer and studied a car I printed several years ago--and I can see the same flat pattern!  However, it's so imperceptible I would have never noticed it had I not tried to find it. The roof looks more blurry, which in this case was a good thing.

I think that Ed's hunch is correct.  It's always been there (at least with the Photon software), but it's now noticeable due to the higher resolution of the new 8K printer.