Save as .DWG - arcs become line segments and circles become octagons

I am using DWG trueview (by AutoCAD) to look at DWG files. Could it be the problem?

You’re not using a properly configured export scheme when you save to DWG.
If you model is in Inches, try CAM Imperial. If millimeters, try CAM Metric.

Both of these have the option to “Simplify lines and arcs” enabled with an appropriate tolerance.

You may want to spend a little time familiarizing yourself with the options and what they do.
The expectation is you will modify the named schemes or make your own that best suit your needs for conversion to DWG/DXF.

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Do you want the arcs to become segments or are you complaining that they are? To expand on what John said, there are options in the export schemes to either preserve arcs, etc. or to convert them depending on your needs.

I suspect Bassist using the placeholder “Default” export scheme that converts everything to flat, segmented polylines based on a 20 degree deflection angle.

I tried CAM imperial with multiple options but still both curves and circles change to segments. My 2d drawing has many .125 diameter circles, no mater what scheme options I choose, still end up as octagons in the DWG file. Note: this is my first time trying to save as a DWG so I’m very “green” at it.

Well, here anyway, arcs and circles stay arcs and circles in the Default Export DXF scheme. He may have used 2004 polylines or something.


I just exported 100 .125 dia. circles with CAM Imperial and they are all circles on re-import to Rhino…


I’ve attached 125_circle.3dm with a 1/8" diameter circle in it and 125_circle.dwg made from it using the CAM Imperial export scheme. I’ve also included a screenshot of the settings in CAM Imperial.
This DWG file should open in AutoCAD as a circle

125_circle.3dm (22.3 KB) 125_circle.dwg (17.1 KB)

I don’t know.
Does the DWG file I sent open correctly in this “trueview” tool?
It opens correctly in AutoCAD itself.

Years ago, in AutoCAD itself, there was a command called ViewRes (I think). It’s been 25+ years… That had a similar effect on the display of circles. If you set the ViewRes to something very coarse, it would dramatically speed up the display performance in large files. Maybe this TrueView tool has something similar.

Been moving lines, arcs and splines to Autodesk Fusion lately with success. Not sure if such translate to TrueView. While I did not experiment with most of the options, here is what worked.

  1. Explode any polylines (anything joined) and ungroup anything grouped
  2. Export DXF default

You can try regen command in AC…

John is correct.
Once you have a DWG open in Trueview, from the drop-down menu you can select options.
On the “Display” tab, you have ‘Display Resolution’ for ‘arc & circle smoothness’, and for 'segments in a polyline curve’
Set these to 5000 or 10000 and 8 or 16 respectively and I am sure you will see the difference.
The lower the number, the more tessellated the curve and designed more so for lower end graphics cards.

For anyone not familiar with Trueview, Autodesk release it alongside each AutoCAD release (for free) BUT it also includes DWG-Convert. It will convert any AutoCAD DWG file from one format to another, back as far as R-2000 versions.
Very handy is you receive 2013 format files and can normally only open 2010 format etc.