I was reading about how a 3d dxf creates true arcs and circles instead of segmented, but I don’t see a 3d dxf export option.
what am I missing?
Try looking under File>Export>3D Model… instead of 2D Graphic.
Hhmmm, thanks Dave but look at this export. It just fills a tiny part of the 3d dxf, and there are quite a few lines crossing the dxf. Is this how it should be? I don’t think my CNC guy can work with this?
What scale did you use when you imported it? Share the .skp file so we can see what you’ve got.
I’m trying to export it Dave, and I don’t see any Scale options.
the skp file is way too big to post here.
I asked what the import scale was not export.
Upload it to DropBox and share the link.
I’d rather not post the whole model Dave,
what I’m trying to do is export individual dxf for each of the rafters which I have cut by cnc. I’m hoping the 3d dxf will make all the curves true.
C’mon Joe, this isn’t your first rodeo. Copy one of the parts into a separate SketchUp file and upload that.
Do I understand right that your CNC guy only needs your part outline in the DWG/DXF? In that case you can uncheck everything else in the Export Options dialog except Edges. The triangular shapes that show in your screenshot are the faces from SketchUp. They always export triangulated and facetted.
Are you exporting directly from the model you show in your screenshot or are you laying out a “part catalogue” on the “ground”? The latter way might be easier for the CNC person
to work with than with edges scattered around in 3D space.
(edit, your latest post anwers my question)
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Make sure each piece is flat on the ground plane and only 2D (isolate one face of the rafter, delete the rest). Then make sure the camera is in parallel projection and in the Top standard view, directly overhead. Export>3d model, set to dxf. open the options button at the bottom of the export window and de select everything except for edges. Then export.
However your edges must be Arcs and not Curves for this to work, select an edge and check entity info upper left to inspect.
CUT ONE RAFTER.skp (94.8 KB)
Looking at the model you posted, I noticed that most of the edges in your rafters are not arcs but separate edges or welded curves. Neither of these will convert back to arcs or Bezier curves when exported.
Yeah OK Anssi I see that this 3d dxf won’t work for me darn it … but thanks for taking a look for me, you too Dave!
I’m going out to the shop for a little while now.
Well, if you wanted to go this route, it is possible to clean up the edges using the center points of the existing arc as a guide. It would just take time and care, of course I chose a random one to clean, others might be harder.
@endlessfix did you use the 2022 SU dxf export feature to do a proper dxf for cnc use after you did the process shown in your gif?
No, I didn’t go that far, not sure the OP was interested. Just showing that restoring the arcs is possible. I didn’t check for “flipped” arcs.
PS. Off topic- I am having much better luck with simple dxf, thanks for your help.
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Yeah you can see why the top edge of these rafters are all cut up in short segments, the bottom edges I make true arcs increasing the segments where I need them, esp the curved rafter tails.
it’s so cool how my cnc guy can cut these from 2x12" 
Each rafter is perfect and all the roof pieces almost snap together!
Something I haven’t seen mentioned so far, when doing a 3D DXF export, you would want to uncheck Faces. If Faces is selected you get one set of true arcs (if your model used arcs and circles), and you also get line segments on top of those. Unchecking Faces will get rid of the line segments.
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As I assume you have some input to the programing folks at SU, may I suggest that all these discussions about curves, or lack of in SU, I find beyond ridiculous. Every vector graphics program I’ve ever known - and there are quite a few - can produce a perfect circle, or Bezier curve. Why can’t the programmers at SU get off their duff, and bring SU up to speed, because there is a very, very good reason to do so. I contacted a very knowledgeable friend about this issue, and here is my question to him, and his response:
-----Original Message-----
From: Jim Clark jamesoliverclarkthethird@gmail.com
Sent: Wednesday, August 3, 2022 1:18 PM
To: Allen Razdow arazdow@truenum.com
Subject: Ones and Zeros question
The thing I dislike about Sketchup the most is that there is no such thing as a curve in Sketchup, only straight lines. So, there are two icons for doing either a circle, or polygon. They are the some thing, except the circle has 24 straight line segments, and the polygon has 6. If you want to display a large circle that will appear as a “true”
circle, then you have to increase the amount of segments to a large number, such as 1,000. We’re talking a lot of data points for just this one circle. If the circle is repeated many times in the model … well, you get the picture. Other vector graphics programs, such as CorelDRAW and AutoCAD, produce a true circle. My question is this: It seems to me that a true circle instruction sent to a graphics card would be far, far simpler, from a processing standpoint, to display, as opposed to the Sketchup instruction. Am I on, or off on with this assumption?
Here is Allen’s response
You are correct. Generally, some method of approximating curves is used, such as “cubic splines”, and special cases for circles and ellipses. A true solid modeler like SolidWorks stores the math for these shapes so it can compute intersections and extrusions correctly at any scale.
@jim9 It would be wise to edit your previous post and remove any personal details, such as emails. It’s against forum rules for good reason as they are almost certainly harvest by web crawling bots to compile spam email lists.
SketchUp is a surface modeler, the implication that non segmented arcs and circles would be trivial to adopt is incorrect. Comparing with SolidWorks is comparing submarines with helicopters, both cool machines, but very different goals.
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